CHAPTER ELEVEN

DIATOM FLORA OF THE WARRI/FORCADOS ESTUARIES

11.1The Diatom Genera of the Warri/Forcados Estuaries

The taxonomic classification of the diatom species collected from the Warri/Forcados River Estuary, with descriptions follows. The class Bacillariophyceae is divided into two orders, Centrales and Pennales. The present knowledge permits a subdivision of the two diatom orders, Centales and Pennales into five suborders and 21 families according to Simonsen, 1979. Of the five suborders, three, Coscinodisneae, Rhizosoleniineae, and Biddulphiineae belong to the Centrales, while two—Araphidineae and Raphidineae belong to the Pennales.

Division BACILLARIOPHYTA

Class BACILLARIOPHYCEAE

Order Centrales

Suborder Coscinodiscineae

Family Thalassiosiraceae Lebour 1930, emend Hasle 1973

Aulacosira Twaites

Cyclotella Kütz. Lauderia Cleve Planktoniella Scütt Thalassiosira Cleve

Family Melosiraceae Kützing 1844

Leptocylindrus Cleve

Melosira C. A. Agardh

Family Coscinodiscaceae Kützing 1844

Coscinodiscus Ehr.

Family Hemidiscaceae Hendey 1937, emend Simonsen 1975

Actinocyclus Ehr.

Family Heliopeltaceae H. L. Smith 1872

Actinptychus Ehr.

Family Rhizosoleniaceae Petit 1888

Guinardia Peragallo

Rhizsolenia Brightwell

Family Biddulphiaceae Kützing 1844

Subfamily Hemiauloideae Jousê, Kiselev & Poretskii 1949

Eucampia Ehr.

Hemiaulus Ehr.

Subfamily Biddulphioideae Schütt 1896

Biddulphia Gray Hydrosera Wallich Terpsinoe Ehr.

Family Chaetoceraceae H. L. Smith 1872

Bacteriastrum Shadbolt

Chaetoceros Ehr.

Family Lithodesmiaceae H. & M. Peragallo 1897–1908

Ditylum Baily

Family Eupodiscaceae Kutzing 1849 Subfamily Eupodicoideae Kutzing 1849 Odontella C. A. Agardh

Pleurosira (G. Meneghini) Tresisan di San Leon 1848

Shuelta Triceratium Ehr.

Order Pennales

IV Suborder Araphidineae

Family Diatomaceae Dumortier 1822

Fragillaria Lyngbye

Synedra Ehr. Tabellaria Ehr. Thalassionema Grun.

V. Suborder Raphidineae

Family Eunotiaceae Kützing 1844

Eunotia Ehr.

Family Acanthaceae Kützing 1844

Cocconeis Ehr.

Family Naviculaceae Kützing 1844

Amphiprora Ehr.

Amphora Ehr. Anomoeoneis Pfitzer Caloneis Cleve Cymbella C. A. Agardh Diploneis Ehr.

Frustulia Rabh. Gyrosigma Hassal Navicula Bory Pinnularia Ehr.

Pleurosigma W. Smith

Family Nitzschiaceae Grunow 1860

Bacillaria Gmelin Hantzschia Grun Nitzschia Hassal

16 Family Surirellaceae Kutzing 1844

Stenopterobia Brêb.

Surirella Turpin

11.2The Study Area

Figure 14 represents the Warri/Forcados Estuaries of Southern Nigeria. Located between latitude 5o and 6o East, the study area forms part of the anastomosing creeks traversing the Southern coastline of Nigeria. It is derived from the merging and convergence of the Warri and Forcados Rivers and their tributaries. From an average width of about 100 metres in the narrowest parts, it spans over 3 kilometres in the widest regions before emptying into the Atlantic Ocean at South Point within the Bight of Benin.

The drainage basin is typically of rain forest formation and covers approximately 2,627 square kilometres. The entire waterway, which is over 80 kilometres long, is affected by strong tidal action especially in the dry season months. Apart from the typical mangrove trees, the other fringing vegetation included swamp trees interspersed with grasses, ferns and various emergent macrophytes. The area enjoys a tropical climate, with well demarcated rainy and dry seasons. The dry season stretches from November to April while the rainy season usually from May to October. The average annual rainfall is 2,500 mm, while the mean maximum hourly rainfall is 100 mm (S. P. D.C., 1988). The minimum air temperature recorded is 18oC, while the maximum is 35oC, with a mean

oo

Figure 14: Map of the study area, with an inset showing its position (arrowed) in Southern Nigeria, and the location of the sampling stations along the estuary

Figure 14: Map of the study area, with an inset showing its position (arrowed) in Southern Nigeria, and the location of the sampling stations along the estuary

Figure 15: The conductivity isopleths of the Warri/Forcados Estuary along the sampling route. The shaded areas below 1000 µS cm–1 indicate freshwater zones

Figure 16: The salinity isopleths of the Warri/Forcados estuary along the sampling route. The ushaded portions represent brackish waters.

Figs. 15 and 16 represent the conductivity and salinity isopleths along one stretch of the estuary covered by the study between the months of February and September 1985. The 500 µS cm–1, conductivity isopleths, roughly approximating to 0.5‰ salinity, served to demarcate the true freshwater zone from brackish water. The freshwater zone was further divided into two sub- zones—an area of less than 100 µS cm–1 and another between 500 and 1000 µS cm–1.

A mixing zone of between 500 and 1000 µS cm–1 formed the transition band between freshwater and brackish water.

The extent of distribution of freshwater along the estuaries at any time of the year was found to be variable and closely correlated with the geographical position of the transition zone between the saline and freshwater zones. The transition zone is affected by the interplay between the tidal range and the volume of water discharge or runoff. The transition zone is near the mouth of the estuary when there is a relatively small tidal range and a large runoff; it is near the headwaters or river source when there is a large tidal range and a small runoff. As the rains come with higher precipitation, the volume of river discharge increases, and the transition zone gradually moves downstream until over 80% of the estuary is occupied by freshwater between the months of July and October (Opute, 1990).

11.3Taxonomy and Description of Species

11.3.1Order CENTRALES

Suborder: COSCINODISCINEAE

Family: THALASSIOSIRACEAE Lebour 1930, emend Hasle 1973 Genus: Aulacoseira Twaites 1848

The genus was resurrected to separate freshwater Aulacoseira from Melosira, a primary marine genus. The centric frustules of the genus Aulacoseira are linked to one another by spines to form filaments. Cells are typically seen in girdle view because of the deep valve mantle. The mantle is highly ornamented. Cells often form colonies and, depending on the species, may be joined by linking spines. Rimoportulae are present on the valve mantle and are often associated with the ringleiste, an internally thickened ring of silica. The external expression of the rimoportulae may be simple pores while internally they may form complex structures. Aulacoseira is one of the most common freshwater diatom taxa, abundant in lakes and large rivers.

Aulacoseira granulata (Ehrenberg) Simonson (Plate 1)

Formerly known as Melosira granulata (Ehr.) Ralfs. Cells between 9–24 µm wide with a mantle height of 4–20 µm; presence of a sulcus which is shallow; frustules cylindrical, join face to face and form filamentous colonies. Valves with short marginal teeth and elongated spines; punctae large and indistinct; girdles coarsely punctuate with parallel straight striations of about 7–9 in 10 µm. Colonies usually straight, but sometimes spiral, with curved cells. Distribution: planktonic and restricted to freshwater habitats.

Plate 1: Aulacoseira granulata (a) Light microscopy (LM); (b) Hand drawing (HD); (c) & (d) Scanning Electron Microscopy (SEM).

Aulacoseira granulata var. angustissima Mueller (Plate 2)

Frustules very narrow, cylindrical and terminated by long spines. Diameter of cell, from 4–6 µm. Ratio of mantle height to valve diameter is greater than 3.2. The mantle has straight sides, and the valve face is flat. Linking spines, short and bifurcated are located at the end of each pervalvar costa.

Plate 2: Aulacoseira granulata var. angustima Mueller (a) LM, (b) SEM

Aulacoseira granulata var. angustissima f. spirilis (Hustedt) Czarn. & Reinke (Plate 3)

Cells narrow, cylindrical and forming helical filaments of different degrees of spirals or coils. A survey of the diatom flora along the Nigerian coastal water ways from Lagos to Calabar in Cross River State shows that this taxon is limited so far to the Niger Delta.

Plate 3: A. granulata var. angustima f. spiralis (a) LM; (b) SEM; (c) & (d) HD

Aulacoseira ambigua (Grunow) Simonsen 1979 (Plate 4) Synonyms: Melosira ambigua (Grunow in Van Heurck) O. Mull. Colonies are usually straight, but sometimes spiral filaments with curved cells. Frustules cylindrical, valves 3–12 µm in diameter with mantle height of 5–15 µm. The ratio of the mantle height to valve diameter is greater than 1. The mantle has straight sides, and the valve face is flat with slightly convex margins. Areolae round to square in shape. Spines are located at the end of each pervalvar costa.

Plate 4: Aulacoseira ambigua LM

Aulacoseira muzzanensis Krammer 1991 (Plate 5)

Formerly known as Aulacoseira granulata var. muzzanensis Simonsen

Frustules are cylindrical and form colonies consisting of separate cells. Valves between 9- 24µm in diameter, with a mantle of 5–13µm. The mantle has straight sides, and the valve face is flat or slightly convex or concave. The rows of areolae are almost straight and parallel to pervalvar, but often curved. Linking spines are short, triangular or bifurcated, and are located at the end of each pervalvar axis. The structure of the frustules is essentially the same as in A. granulata with all characteristics overlapping between the two species.

Plate 5: Aulacoseira muzzanensis LM

Genus Cyclotella Kuetzing 1834

Cells solitary, filamentous or colonial in a gelatinous matrix; discoid and drum-shaped; valve view circular or sometimes elliptic; ornamentation of valves in two concentric regions, an outer zone which is radially striate and an inner zone which is smooth and finely punctuate; girdle view straight or undulate; numerous discoid chromatophores.

Cyclotella bodanica Eulenstein (Plate 6)

Frustules solitary, usually united by mucilage. Valve circular with outer zone of prominent striae, 12–14 in 10µm; inner zone irregularly punctuates. Diameter of cell between 40–55µ.

Cyclotella litoralis (Plate 7)

Cells of C. litoralis in girdle view are drum-shaped and undulate with numerous disc-shaped chloroplasts. Valve surface circular in outline with a highly variable diameter from 20–60 µm.

It is clearly demarcated into two distinct concentric zones: an outer striate part and a central non-areolar field. The outer marginal zone has well defined robust striae occupying half the radius of the cell; central zone characterised by rough furrows. Lange and Syvertsen (1989) described this species found in the southwestern Atlantic from collections from nearby Sierra Leone, West Africa as a littoral plankton assemblage.

Plate 6: Cyclotella bodanica, (a) girdle view (b) valve view

Cyclotta litoralis SEM valve view (7a) Whole view (7b) Enlarged

Genus Lauderia Cleve 1897

Cells short and cylindrical, united in chains by fine threads. Valves slightly depressed in the mid-region and numerous conspicuous intercalary bands, which are collar shaped. Centre of the valve convex, with rounded margin. Cells with one large unpaired spine and numerous small gelatinous threads on the valve face and margin. Chromatophores numerous small plates. Cell nucleus suspended in a chord of cytoplasm, which binds the central parts together and helps to form the chains.

Lauderia borealis Gran 1900 (Plate 8)

Cells close together in thick straight chains, touching by their valve surfaces. Valve slightly indented in the centre, rounded at the margins. Marginal spinulae straight with gelatinous straight radiating threads. Chromatophores numerous small lobes, clustering around opposite ends of cells under high light intensity. Cell colour, yellow brown. The nucleus roughly central, in a cytoplasmic cord, connecting centres of valves; sometimes elongated and bi-lobed. Intercalary bands on the entire cell wall, with about 16 punctae in 10 μm. Cell diameter, 28–50 μm.

Plate 8: Lauderia borealis (a) Drawing (HD) (b) Photomicrograph (LM)

Genus Planktoniella F. Schütt 1892

Typically, a warm water diatom species, reported from tropical waters of marine and estuarine ecosystems. Genus hitherto consisting of two species, Planktoniella sol and Planktoniella blanda until Coenobiodiscus muriformis was transferred to the genus Planktoniella (Round, 1972). The genus Planktoniella is characterised by the presence of organic extrusions from the girdle which are of different morphological types. Cells discoid, solitary (P.sol) or in flat colonies (P. muriformis) with a hyaline wing-like expansion all around, consisting of extracellular chambers. Areolae seen in radial tangential rows. Organic extensions of the girdle are characteristic of this genus. The wing like expansion is weakly siliceous and serves as an organ of flotation. Valves areolated like those of Coscinodiscus excentricus. Chromatophores numerous small plates which lie along the valve surface.

Planktoniella muriformis (Loeblich III, W. W. Wight & W. M. Darley) Round 1972 (Plate 9)

Tropical, colonial, centric marine diatom composed of a single cell layer of between 200–530 cells, linked girdle to girdle in a compartmentalized matrix. Colony shape slightly concavo- convex disk, approximately 400 μ. in diameter. Each cell is about 10 μ, in diameter; valves with several structural features in common with those of Thalassiosira. The organic matrix contains 6–11 partitions that radiate from each cell, forming several extracellular chambers.

Plate 9: Planktoniela muriformis (LM)

Species formerly described as Coenobiodiscus muriformis but recently transferred to the genus Planktoniella (Round, 1972).

Genus Thalassiosira P. T. Cleve, 1873 emend Hasle, 1973

Thalasiosira spp, are an important component of phytoplankton populations, and most species are cosmopolitan. Cells disc or drum-shaped, connected through a central organic thread to flexible chains, but in some cases, cells are connected through several threads to chains, or they are embedded in irregular-shaped mucilage colonies, or they occur as single cells. Pervalvar axis usually shorter than the diameter in girdle view. Valve face flat and mantle smoothly curved. External tubes of the marginal strutted processes readily seen in light microscopy. Valve view reveals hexagonal areolae (8–18 in 10 µm) in curved tangential rows. The circular, areolated valves possess one or sometimes several central and always marginal strutted processes. They can also be distributed over the whole valve surface. Marginal processes widely spaced. Labiate process large and always located closely to one of the marginal strutted processes. For species identification, cell shape, occurrence as single cells, as chains, or in mucilage colonies; number, arrangement and morphology of strutted and labiate processes, presence of occluded processes, presence of an annulus, girdle band morphology, ornamentation/areolation details are of interest. Several of the characteristics used for species identification are scarcely or not at all visible in the light microscope. Chromatophores numerous, small, and plate-like.

Thalassiosira anguste-lineata (A. Schmidt) G. Fryxel & Hasle 1977 (Plate 10)

[Basionym: Coscinodiscus anguste-lineata A. Schmidt; syn.: Coscinodiscus polychordus Gran. Thalassiosira polychorda (Gran) Jorgensen; Coscinosira polychorda (Gran) Gran]

Cells usually wider than high in girdle view. Valve with eccentric areolation; valve face flat and valve mantle shallow. Central strutted processes in clusters between 1 and 3 in a central ring; one marginal ring of conspicuous strutted processes. One labiate process is located between two marginal strutted processes, lying just inside the marginal ring of strutted processes. In girdle view cells appear rectangular. Connecting threads (in a cluster of 3–6) link adjacent cells. Connecting threads distinct and visible in girdle view under light microscopy. 3–6 marginal processes occur within 10 µm. Cells 14–78 µm in diameter; chromatophores numerous, small and rounded.

Plate 10: Thalassiosira anguste-lineata (SEM) with different magnifications

Thalasiosira ferelineata Hasle and Fryxell 1977 (Plate 11)

Valve circular in outline. Valve face flattened; valve mantle shallow, slightly slanting; border between valve face and mantle rounded. Valve margin made of horizontal, broad brim; diameter 20–43 µm. Hexagonal loculate areolae mostly in straight rows. Internal cribra hexagonal to circular in outline.

Plate11: Thalasiosira ferelineata: SEM in different magnifications

Valve mantle areolated to horizontal brim with one labiate process on edge of valve face. One marginal ring of strutted processes closes to the valve margin, about 3 to 4 in 10µm, separated by about 6 areolae. Marine planktonic species. Previously described by Hasle and Fryxell (1977) from Peru in South America.

Thalassiosira hendeyi Hasle & G. Fryxell 1977 (Plate 12) [Synonym: Coscinodiscus hustedtii Müller-Melchers]

Cells rectangular in girdle view, with slightly shorter pervalvar axis than the diameter and a slightly undulating marginal ridge. Cells with straight/linear areolation with relatively coarse hexagonal areolae. Valve face covered with minute siliceous granules.

Plate 12: Thalassiosira hendeyi (SEM) (a) Tilted girdle view (b)Valve exterior (underneath) Tilted girdle view (d) tilted view showingboth valve and girdle (e) & (f) close up view showing areolae

Presence of one tiny central strutted process and three marginal rings of small, strutted processes. Two labiate processes with prominent external tubes on opposite sides of the valve. In natural samples the species occurs single celled but may also form short chains. The areolation and labiate processes are easily visible in light microscopy in living cells.

Thalassiosira leptopus (Grun.) Hasle et Fryxell 1976 (Plate 13)

Basionym: Coscinodiscus leptopus Grun. in Van Heurck 1883.

Synonym: Coscinodiscus lineatus Ehrenberg 1854.

As seen in SEM the valve face is flattened, and the mantle is shallow, no sharp angle between valve face and mantle. Areolae are basically hexagonal and of the loculate type with a wide circular foramen. The areolae of the face valve are in straight rows, while those of the valve mantle are much smaller and irregular in arrangement. There are 4–7 areolae in 10 µm on the valve face. Cells typically have prominent marginal processes together with finely areolated valve mantle. Three types of marginal processes are present: one large labiate process located in the slanting valve mantle, numerous small marginal strutted processes arranged in zigzags in 2–3 rows, and one marginal ring of irregularly spaced larger occluded processes. Distribution: Gerloff and Helmeke (1974), Simonsen (1974) and Hasle and Fryxell (1976) have reported T. leptopus from the Indian, Atlantic and Pacific Oceans. Our report is from the Atlantic Ocean.

Plate 13: Thalassiosira leptopus SEM different magnificationsThalassiosira minima Gaarder (Plate 14)

Synonym: Coscinodiscus floridana (Cooper) Hasle, Thalassiosira floridana (Cooper) Hasle). Cells 5–15 µm in diameter. Valve with radial radial rows of areolae. Two or sometimes one central strutted process with a short external tube. One marginal ring of seven to twelve tube- like strutted processes. Rectangular cells in girdle view. Cells connected into chains with the connecting thread twice as long as the pervalvar axis. Chloroplasts, few and rounded. Thalassiosira minima is a cosmopolitan species except in Polar Regions.

Plate 14: Thalassiosira minima SEM

Thalassiosira rotula Meunier 1910 (Plate 15)

Cells generally discoid, flat, and considerably wider than high in girdle view. In natural samples the species occurs in chains with relative short connecting threads. Threads extend from a cluster of central strutted processes.

The central connecting threads are easily visible as a single thick thread in LM. Valve with fine radial ribs and areolation only at the margin. Marginal rings of relatively small, strutted processes, several of which are scattered over the valve face. Cells 8–60 µm in diameter, 5–20 µm in height (pervalvar axis) and with numerous chromatophores.

Plate 15: Thalassiosira rotula SEM

Plate 15: Thalassiosira rotula SEM

MELOSIRACEAE Leptocylindrus

Cells long, cylindrical, united into chains by whole valve surface. Valves flat, without spines or processes. Intercalary bands present, weakly visible. Cells thin-walled, hyaline, without visible sculpturing. Chromatophores one or many roundish plates or granules.

Leptocylindrus danicus Cleve (Plate 16)

Frustules narrow and cylindrical, 4–7 times longer than broad and joined in closed long filamentous chains. Valves flat or convex, occasionally concave, without visible sculpturing. Intercalary bands present but difficult to see. Chromatophores discoid, few to many, not very small, distributed throughout the valve surface. Cells widespread in distribution, planktonic and found in brackish waters.

Plate 16: Leptocylindrus danicus Cleve (LM)

Genus Melosira Agadh 1824

Cells cylindrical to subspherical, closely united into long filaments by mucilage pads secreted onto their valve faces; in addition, irregular spines may assist the linkages. Valve faces flat or domed, covered with small spines or granules. Valve view circular; valves with or without marginal teeth; girdles with or without sulcus. Melosira valves have little ornamentation. Lack distinctive features including costae, septae, and spines. Frustules form long colonies linked at the valve face. Chromatophores numerous, small discoid and packed together. A common genus in freshwater and marine epibenthic habitats.

Melosira moniliformis (Mueller) Agardh 1824 (Plate 17)

Cells pill-shaped, from roughly cylindrical to almost spherical; usually connected in straight chains by mucous pads. Valves circular, convex and thick-walled, with intercalary bands. Chromatophores numerous and discoid, located along the cell wall, nucleus central. Cells yellow brown in colour; distribution, freshwater. Cell diameter 20–50 µm.

Plate 17: Melosira monoliformis LM

Melosira nummuloides Agardh 1824

Frustules elongate and globose, united in pairs by girdle bands to form chains; valve surface circular and convex with radiating punctae. Restricted to the lower reaches of the estuaries with salinities below 10‰.

Melosira varians C. Agardh 1827 (Plate 18)

Cylindrical cells, rectangular in girdle view, often forming long chains of linked cells. Valve faces slightly convex and covered with small spines. Little or no ornamentation (areolae) on valve faces unlike many Aulacoseira species. Commonly found in benthic habitats in eutrophic freshwater in rivers and lakes; can form long filaments along the margins of rivers where current is weak. Cell size: length 5–30 µm, width 5–15 µm.

Plate 18: Melosira varians LM

Family COSCINODISCACEAE Kutzing 1944

Genus Coscinodiscus Ehrenberg 1838

Cells disc or box-shaped, unicellular, rarely in twos after cell division. Valves circular with hexagonal areolae arranged in different ways and usually radial.

Coscinodiscus centralis Ehrenberg (Plate 19)

Valves discoid and convex with a distinct central rosette of large areolae decreasing in size towards the periphery. Margins of valve equipped with small spinulae and two large processes, apiculi, at an angle of 90o between them. Diameter, 200–300 µm.

Plate 19: Coscinodiscus centralis LM

Coscinodiscus concinnus W. Smith 1856 (Plate 20)

Cells drum-shaped, large with convex valves, flat or slightly concave in the centre. Valves thin- walled, areolation delicate with a central rosette. Marginal spinulae and the presence of two small apiculi. Diameter of valve 150–260 µm.

Plate 20: Coscinodiscus concinnus LM

Coscinodiscus jonesianus (Greville) Ostendfeld 1915 (Plate 21)

Cells are solitary and free living with valve shape round or disc-like. Valve surface slightly convex, with the valve mantle curving towards the margin. There are two prominent labiate processes, called apiculi or rimoportulae on the margin separated by an angle between 105 to 120o. Under the light microscope the central hyaline area is not very clear. In the scanning electron microscope, the central hyaline area was conspicuous with distinct areolae, valve face flat or slightly depressed. The cell girdle view is drum-shaped and convex. Valve diameter between 200–260 µm. The areolar pattern is fasciculate, forming spiral decussate arcs towards the valve centre. This is the first tropical report of this diatom made by Mills in 1932 in his samples from Warri River followed by Hendey in 1958 in his publication titled “Marine diatoms from some West Africa Ports.

Plate 21: Coscinodiscus jonesianus: Different SEM views - (a) valve view showing macrorimoportulae; (b) (c) & (d) tilted view showing girdle view; (e) enlarged valve view showing macrorimoportulae with conical structures.

Coscinodiscus jonesianus var. warriensis var. nova (Plate 22)

Like the type species, cells of the variety are solitary and free living with valve shape round or disc-like. This is an abundant tropical estuarine diatom taxon reported for the first time from the Warri River estuary. In addition to the prominent macrorimoportulae, labiate processes, peculiar to Coscinidiscus jonesianus, a number of distinctly prominent tubular spines, microrimoportulae, (measuring 10–12 µm in length, are present, radially and irregularly distributed towards the margin of the valve surface. These are easily seen under the light microscope.

Plate 22: Coscinodiscus jonesianus var. warriensis: (a) valve view LM; (b) & (c) SEM showing distinct spines (microrimoportulae arranged irregularly near the margin).

Coscinodiscus oculus-iridis Ehrenberg 1939

Cells, discoid with polygonal areolae arranged in radiating rows. Areolae, which are larger from the outside and diminishing towards the centre, have a characteristic “eye spot” appearance. Diameter, 160–260 µm.

Family HEMIDISCACEAE Hendey 1937, emend Simonsen 1975.

Genus Actinocyclus Ehrenberg

Actinocyclus is a genus of diatoms in the family Hemidiscaceae. The genus Actinocyclus is defined as having a single peudonodulus, radial areolation sometimes in isolated single rows, and abrupt transition in areolation pattern from valve face to mantle, and marginal ring of large labiate processes. Recent examination in both the light and scanning electron microscope (von Sydow and Christenhus 1972, Ross and Sims 1973, Fryxel and Hasle 1973, Hasle 1977, Fryxell and Semina 1981, and Sullivan 1983) also support these morphological features as diagnostic of Actinocyclus. An origin of Actinocyclus from Coscinodiscaceae has been suggested (Ross and Sims 1973, Simonsen 1975, 1979) and for taxonomic purposes the presence or absence of pseudonodulus has been critical for identification of a taxon such as Actinocyclus (Villareal and Fryxell, 1983).

Actinocyclus actinochilus (Ehrenb.) Simonsen 1982 (Plate 23)

Cells solitary, cylindrical to discoid. Valves flat with rounded edges, 120–175 µm in diameter. Areolae in isolated radial rows that are sometimes curved or incomplete, areolation variable; areolae 7–13 in 10 µm, with foramen on the inside, bordered by thickened rim. Marginal labiate processes variable, about 6–10 in each cell and 12–15 µm apart in the inner surface of valve. Striae in valve mantle. Chloroplasts numerous and discoid.

Plate 23: Actinocyclus achinochilus (a) Valve view; (b) SEM with labiate process; (c) SEM showing central area

Actinocyclus octanarius Ehrenberg 1838 (Plate 24)

Cells drum-shaped with a flat pronounced valve face with abruptly curving mantle. Cells solitary with circular valves. Central annulus variable, hyaline to completely areolate at the centre. Pseudonodulus (a large pore in the valve) is visible. Numerous chloroplasts occur around the cell margin.

Plate 24: Actinocyclus octanarius SEM, different magnification

Genus Azpeitia M. Peragallo 1912

000000The genus Azpeitia M. Peragallo was created and described in 1912 by Peragallo from fossil material. Originally, Azpeitia Peragallo was described as a monotypic genus, with its type species being A. antiqua. Many of the species belonging to Azpeitia were originally placed in Coscinodiscus (Fryxell et al., 1986). The genus is characterised by valves with nearly a central rimoportula, often on the edge of an annulus; a ring of rimoportulae on the edge of the valve mantle; specialized areolae patterns on the mantle differ from those on the valve face. All species are warm water in distribution in tropical/subtropical waters. A sequence of symmetry, from biradial (approaching radial) to dissymmetry is noted in Azpeitia and in related genera, which include Actinocyclus, Roperia, and Hemidiscus.

Azpeitia africana (Janish ex A. Schmidt) G. Fryxel & T. P. Watkins 1986 (Plate 25)

Azpeitia africana shares with other members of Azpeitia an external cribrum, an internal foramen, a labiate process positioned on the edge of a central annulus, and a marginal ring of labiate processes. On this basis, A. africana was moved out of the genus Coscinodiscus as reported by Fryxell, Sims and Watkins (1986). However, A. africana differs from other living species of Azpeitia in that the nearly central labiate process tube through the valve is recessed externally. The valve is disc-shaped with radial areolae in decussating arcs, similar to that of Coscinodiscus. Azpeitia africana has been found in the Gulf Stream, central Pacific and the Gulf of Mexico. It can be classified as warm water, marine planktonic species.

Plate 25: Azpeitia africanaSEM (a) valve view; (b) higher magnification showing labiate processes; (c) central region

Family HELIOPELTACEAE H. L. Smith 1872

Genus Actinoptychus Ehrenberg 1841

Cells disc-shaped, usually single, in rare cases joined in twos or threes; valves divided into sectors which are alternatively raised and depressed. Smooth central area. No intercalary bands. Cell wall usually of several layers with individual membranes punctuated; punctae in crossing lines, more or less strongly areolated. Areolation strongest on the outer layer, on the inner membrane often entirely lacking. On outer margin of the sectors, often only in raised ones, one or more claw-like processes communicate with the inner cell by a pore canal. Valve margin more or less wide and often with numerous marginal spinulae. Species mostly marine, preferably littoral, and found in the plankton.

Actinoptychus splendens (Shadboldt) Ralfs in Pritch. 1861 (Plate 26)

Cells disk or drum-shaped, single or in irregular colonies; valves radially undulate, 70–100 µm in diameter. Valve view circular with 16–18 sectors alternatively raised and depressed (in our specimens illustrated, 18 sectors). Central space nearly circular or star-shaped and hyaline. Areolations of all sectors in most individuals are faint but may be robust.

The raised sector terminates in short blunt spatulate process from which a more or less sharply marked, structureless hyaline line runs towards the inner end of the sector. The depressed sector has a slight swelling in place of the processes. Punctuation on all sectors similar; the punctae in decussating oblique rows, 11–14 punctae in 10 µm. In girdle view valve surfaces appear twisted. Our taxon, a typical estuarine species found in the plankton and causing blooms at the onset of the dry season in November/December between salinities of 3 and 6‰. Diameter, 79- 96 µm.

Plate 26: Actinoptichus splendens (a) valve view, (b) girdle view both LM; (c) valve view, (d) girdle view both hand drawing; (e) & (f) girdle view, single & two cells, respectively both SEM

Suborder RHIZOSOLENIINEAE

Family RHIZOSOLENIACEAE Petit 1888

Genus Guinardia H. Peragallo 1892

Frustules cylindrical, longer than broad with a straight or slightly curved pervalvar axis united in a close-set. Valves circular with flat surface; with an asymmetrical lateral rudimentary tooth occurs on the valve margin. Numerous roundish, lobed chromatophores are present. Nucleus usually lying in a central plasma mass, suspended by cytoplasmic strands extending to the cell walls.

Guinardia flaccida (Castracane) H. Peragallo 1892 (Plate 27 (a), (b) & (c))

Cells typically cylindrical, between one and half to twice longer than broad, single or united in chains by whole valve surface; valve nearly flat slightly curved with an irregular tooth at the margin. Wall weakly siliceous, without visible sculpturing. Chromatophores numerous, rounded and lying near the wall. Cells neritic, found in the lower reaches of the estuaries with salinities above 12‰. Diameter, 35–80 µm; length (pervalvar axis) 50–160 µm.

Plate 27: Guinardia flaccida filament; (1a) LM; (1b) HD, (1c) Single cell, LM Guinardia striata (d) LM; (e) HD

Guinardia striata (Stolterforth) G. R. Hasle, 1997 (Plate 27 (d) &(e))

[Synonyms: Rhizosolenia stolterfothii H. Peragallo 1888; Eucampia striata Stolterfoth, 1879] Cells large, cylindrical, uniformly curved in close-set spiral chains with flat valves rounded at the edges. Strong spine (process) on valve margin fits into depression on adjacent cell. Intercalary bands numerous and collar-like. Cell wall weakly siliceous without a detectable structure. Chromatophores numerous, small, and oval. Nucleus situated centrally, near the cell wall. Distribution neritic but sometimes oceanic. Diameter, 23–30 µm; length (pervalvar axis) 40–250 µm.

Genus Neocalyptrella Hernandez-Becerril & Meave, 1996

Leaf-like looking centric diatom. Cells solitary, large, bilaterally symmetrical, 108.3–190.6 µm in diameter, 413.3 µm long; elliptical in cross section, crescent shaped in lateral view and of sigmoid form in ventro-dorsal view. Valve conoidal with a rounded or truncated apex and with longitudinal undulations. Process, 6.5–7.3 µm long, 0.8–1.0 µm in diameter is a cylindrical external tube, straightened towards the distal part and merging with the calyptra structure in the distal part of the tip. Valve areolae, 12–16 in 10 µm, arranged in regularly straight striations, with a secondary quincuncial pattern. Otaria, claspers, and contiguous areas are absent. Girdle segments oriented in a straight line and arranged in two dorsiventral columns. Segment areolae, 17–22 in 10 µm, are arranged in regular, straight striations. Horizontal and perpendicular axes of segments 108–190 and 12–25 µm in length, respectively.

Neocalyprella robusta (Norman ex Ralfs) D. U. Hernandez-Becerril & M. E. Meave del Castillo, 1997 (Plate 28)

[Synonyms: Rhizosolenia robusta G. Norman ex Ralfs, 1861.

Calyptrella robusta (G. Norman ex Ralfs) D. U. Hernandez-Becerril & M. E. Meave Del Castillo, 1996]

Cells usually solitary, rarely occurring in pairs; large, robust sickle-shaped in lateral view; valves crescent-shaped and deeply convex with longitudinal lines and ending with a small process short tube inside a circular collar. Valvar plane elliptical, often whole cell curved. Calyptrae with distinct longitudinal lines and excentric process with a fine, bristle-like point and suddenly dilated hollow base. Intercalary bands robust, numerous, typically collar-shaped. Cell wall thin, and siliceous. Chromatophores numerous, lying along the wall. Nucleus near the wall. Cosmopolitan, normally more oceanic than neritic. Width 48–120 µm; length 300–500 µm (with occasional reports of 1 mm).

Plate 28: Neocalyprella robusta (a) LM; (b) HD

Genus Rhizosolenia Brightwell, 1858

Cells cylindrical with elongated pervalvar axis appearing singly or in chains, the elongated ends being blunt, sharp, solid or hollow. Cells usually straight or more or less curved, forming spirally twisted chains. Cross-section elliptical or circular. Intercalary bands usually very numerous, but in some species difficult to see. Cell wall generally thin and chromatophores small and numerous, distributed on the entire cell wall. In some species larger plate-like chromatophores are present.

Rhizosolenia setigera Brithtwell, 1858 (Plate 29)

Cells rod-like or cylindrical, tubular and straight. Valves conical and only slightly oblique; apical processes acutely tapered; thickened for some distance from base, otherwise thin and drawn out into very long, fine, straight spines, frequently reaching more than half the total length of the cell. Cell wall thin, weakly siliceous without distinct or visible structure. Plants neritic and fairly common. Chromatophores numerous, small and elliptical. Diameter and length of frustules (with spine) 425 µm, (without spine) 225 µm; width 10 µm.

Plate 29: Rhizosolenia setigera (a) HD; (b) LM

Sub-order BIDDULPHIINEAE

Family BIDULPHIACEAE Kutzing 1844

Sub-family HEMIAULOIDEAE Jouse, Kiselev et Port 1949 Genus Hemiaulus Heib. 1863

Cells single or united in chains; valves elliptical with two narrow pointed, more or less long polar processes parallel with the pervalvar axis. One or more hyaline claws at the end of the processes. Intercalary bands indistinct or absent, without septa. Membrane strongly or weakly siliceous, finer or coarser areolated or punctuated. Cells bent. Chromatophores numerous.

Hemiaulus hauckii Grunow in Van Heurck 1882 (Plate 30)

Cells long, straight or twisted, fairly occurring in long chains; in broad girdle view oblong terminating in long thin processes, which are strongly pointed. Apical axis 12–35 µm long. Valve surface flat or slightly concave, grooves absent. Valve mantle high, no groove at junction with girdle band. Apertures between cells large because of long processes. Cell wall weakly siliceous, often without visible sculpturing; punctae when visible 16–17 in 10 µm on valves.

Plate 30: Hemiaulus haukii (a) LM; (b) HD

Hemiaulus sinensis Greville 1859 (Plate 31)

Cells broadly elliptical in valve view. Attached together in long, straight or curved chains. Pervalvar axis more or less elongated. Apical cells 15–36 µm long. Valves with slightly convex surface of elliptical outline. Valve mantle high, no groove at base. Cell wall more strongly siliceous than in H. Hauckii, areolated and punctuated. Areolae in the centre of the valve 7–8 in 10 µm; on the base of the mantle11–13 in 10 µm. Intercalary bands visible with special preparation.

Plate 31: Hemiaulus sinensis (a) LM; (b) & (c) HD

Sub-family BIDDULPHIOIDEAE Schütt 1896

Genus Terpsinoe Erenberg 1843

Terpsinoe multipolar, centric diatom. Frustules heavily silicified, elongate, with strongly undulate margins. Internally heavily silicified transverse costae present. In girdle view, distinct transverse costae appear like musical notes. Rimoportulae, positioned near the centre of valve face. Grows commonly in tropical and subtropical regions.

Terpsinoe warriensis (Ehrenberg) Mills 1932 (Plate 32)

Cells elliptical with valve surfaces punctuate and having four septa dividing the surface into segments that are more or less of the same size and shape. Resembles Terpsinoe musica Ehr. in girdle view. In valve view it is broader and the septa furrow, bicapitate at each end. This taxon was first described by Mills (1932) from samples collected from the Warri River, South Nigeria.

Plate 32: Terpsinoe warriensis (a) LM; (b) HD

Family CHAETOCERACEAE H. L. Smith 1872

Genus Bacteriastrum Shadbolt 1854

Widely distributed marine, planktonic diatom. The genus is often associated with Chaetoceros but differs in radial symmetry and fenestration of setae. Colonies tend to lie in girdle view, and the cells separated by the curvature of the basal part of the setae, leaving a small gap between the cells. Cells short and cylindrical; circular in cross section; loosely bound in chains by fusion of numerous setae or bristles arranged regularly around the margin of the cells. Setae of two adjacent cells fused for a short distance beyond the base and later separated further out. Terminal setae curved and not divided, thus differing from others. Cell wall hyaline without visible markings. Intercalary bands absent. Apertures between cells of varying width. Chromatophores numerous, small, roundish, more or less lobed.

Bacteriastrum hyalinum Lauder 1864 (Plate 33)

Cells short and cylindrical almost twice as long as broad and forming straight or slightly curved chains; pervalvar axis often shorter than diameter. Valve view circular, bearing on the margin long wavy setae. In end view the setae are curved. Bifurcation in pervalvar axis (parallel to chain axis) giving cells a hairy appearance. Commonly found in areas of high salinities and neritic. Chromatophores small, numerous. Length 20–24 µm; diameter of cell with setae, 105- 156 µm.

Plate 33: Bacteriastrum hyalinum (a) & (b) valve and girdle view LM; (c) & (d) girdle and valve view HD; (e) & (f) SEM valve views

Genus Chaetoceros Ehrenberg 1844

In valve view cells oval to almost circular, consisting of a valve surface and a valve mantle; girdle view, quadrangular with straight sides and concave, flat or slightly convex ends. On the corners of the long axis (apical axis) are borne long thick or thin setae, bristles or awns. The opposite setae of adjacent cells touch each other usually at the base, become hooked forming a chain with different size of apertures between cells. Length of chains controlled by specially formed end cells, which have short and thick terminal setae. Chromatophores display much variation in between species but are rather constant in size and number within species.

Chaetoceros didymus Ehrenberg (Plate 34a)

Chains straight, 12–13µm wide. Cells four cornered in broad girdle view with concave surfaces. Aperture large, constricted in the middle. Valves with a semicircular protuberance in the centre, visible in broad girdle view. Setae arising from corners of cells and crossing at their base or further out. Chromatophores two per cell each with a pyrenoid located in the protuberance.

Plate 34: Chaetoceros (a) Ch. didynus; (b) Ch. lorenzianus; (c) Ch. peruvianum; (d) Ch. subtilis

Chaetoceros lorenzianus Grunow 1863 (Plate 34b)

Cells united to form short to median straight chains with oval apertures. Valves concave, corners drawn up and touching those of adjacent cells. Foramina are rather wide, lanceolate to elliptical, occasionally almost round. Setae are short, only fused at the point of exit from the valve margin but the basal parts of the setae are not fused. They are occasionally fused for a short distance, and then divergent towards opposite ends of the chain. Terminal setae are about the same length and are directed more or less along the chain axis but remain divergent over their entire length. Setae may be smooth or decorated with rows of punctae. Chloroplasts numerous small plates found in the body of the cell.

Chaetoceros peruvianum Brightwell 1856 (Plate 34c)

Cells solitary, heterovalve, united to form medium straight chains, with oval to semi-oval apertures. Cells broadly rectangular in valve view, with short pervalvar axis. Spines long, coarse, thick with short base arising in pairs from the corners and divergent. Apertures range from narrow to ovoid. Variable in size, from 15–45 µm

Chaetoceros subtilis Cleve 1896 (Plate 34d)

Short chains of few cells, straight, 5–15 µm broad. Cells in girdle view slightly oblong. Apertures quite narrow or absent. Bristles springing from the corners, crossing one another directly at the base, thin, all bent towards the hind end of the chain. Terminal bristles at the front not different from the others, longer and thicker at the hind end, diverging slightly. Chromatophore, one to two per cell. Neritic in low saline habitat.

Family LITHODESMIACEAE H. Peragallo 1897–1908

Genus Ditylum L. W. Bailey 1861

Cells three or four cornered in valve view with a strong central siliceous straight hollow spine and marginal ridge strengthened by radiant ribs. Intercalary bands more or less numerous. Valve surface more or less waved, with usually poorly developed humps on the corners. Outer valve margin more or less strongly waved, giving appearance of lines running from valve to valve. Cells elongated, prism-shaped to cylindrical. Solitary except immediately after division, when they are united in chains by the bristles. Chromatophores small, numerous. Typically, neritic plankton.

Ditylum brightwellii (T. West) Grunow in van Heurck 1883 (Plate 35 a, b, c)

Cells are usually solitary, sometimes in short chains. Cells cylindrical, 2–4.5 times longer than broad; prism-shaped with strongly rounded angles; rectangular in girdle view and roughly triangular in valve view. A large spine extends from the centre of each valve and is surrounded by a marginal ridge. Large central spines are bilabiate processes; marginal ridge made of a ring of small processes called ansulae, or a continuous membrane with multiple slots. The girdle zone is very long and not easily distinguishable from the valves. Chains are connected by the large spines. Scale-like intercalary bands are visible with special treatment. Cell wall weakly silicified. Valves are areolated-punctated, with areolae becoming more delicate toward the outside. A central area around the spine is structureless. Areolae are in radial rows on valve surface, in pervalvar rows on valve mantle. Chromatophores numerous, small and evenly distributed on valve surface.

Ditylum sol (Grunow) De Toni 1894 (Plate 35d)

Cells solitary and triangular in valve view, with a rectangular outline in girdle view. There is a centrally located hollow spine on each valve that is about equal in length to the pervalvar axis. Cells, prism-shaped and characteristically wider than long. Valve view more or less wavy, girdle fluted by equidistant undulations. Sides of marginal ridge grossly concave. Bases of the ansulae, where present, deflected centripetally. Areolae, elongated around the valve centre with slight difference in sizes at both sides of the marginal ridge. Presence and number of ansulae subject to variation.

Plate 35: (a), (b) & (c): Ditylum britwellii (a) valve view, (b) girdle view - both LM; (c) SEM end view (d): Ditylum sol, valve view LM

Family EUPODISCACEAE (Kutzing) Simonsen 1979

Sub-family EUPODISCOIDEAE (Kutzing) Simonsen 1979

Genus Odontella C. A. Agardh 1832

Cells oblong in girdle view, with long spines and raised apical elevations. Often forming chains linked by the processes, with the tubular spines crossing each other. Chromatophores, many, small, and discoid. Marine planktonic or epiphytic. Very abundant throughout the oceans. Valves elliptical or lanceolate, with no separation into face or mantle. Valve face plain or with fine granules, spineless or spines, sometimes with two ridges running on either side delimiting an elliptical area in the centre. At each end there is an elevation, sometimes low and blunt, elsewhere horn-like, which bears an occelus. Wall loculate, with fine external

pores and round internal foramina. Spine’s variable in length, are actually the exit tubes of the rimoportulae, placed in the centre of the valves or close to the base of the elevations, diagonally opposite each other.

Cells solitary or united into filaments. Cell walls strongly siliceous. Taxonomic status; currently recognised as a distinct genus Odontella with the following Biddulphia’ species: aurita, obtusa, edwardsii, mobiliensis, regia and sinensis.

Odontella aurita (Lyngbye) Agardh) 1892) (Plate 36)

A single celled organism with two or more labiate processes per valve, which gives it a distinctive shape. It is the type species of the genus, Odontella. Cells connect to each other using the two horns extending from the end of each cell. Cells of this genus have a very distinct shape. Within the two horns are two spines. Each horn contains an ocellus, or eyespot. Numerous chloroplasts are present, lying against the cell walls. Cells, in straight chains, often found in coastal waters, where they frequently act as an attachment platform for other diatoms. Cultivated industrially for human consumption due to its ability to produce up to 28% of its lipid as eicosapentanoic acid (EPA), a long chain polyunsaturated fatty acid (PUFA).

Plate 36: Odontella aurita (a) HD (b) & (c) SEM

Odontella longicrus (Geville) Hobarn 1983 (Plate 37 (a) & (b)

Cells connected in straight chains, sometimes solitary. Valves elliptic to lanceolate, each with two long tapering and slightly divergent horns. Adjacent cells, united by these horns. Centres of the valve faces are conical, with 1 or 2 divergent long spines extending beyond the horns. Thin siliceous membranes sometimes present between adjacent cells.

Chromatophores numerous, small and located near the valve walls; cell nucleus central. Intercalary region separated from the valves by a pronounced depression. Horns have occeli, spine tips slightly branched. Valves with punctae radiating from a small hyaline central area, forming concentric ellipses on each half of the valve. Intercalary bands sometimes present, finely punctuate, in vertical rows. Cells yellow brown in colour. Large diameter (apical), 15- 110 µm; valve areolae, 12–17 in 10 µm; band areolae, 18–21 in 10 µm. Tropical to temperate in distribution.

Odontella mobiliensis (J. W. Baily) Grunow 1884 (Plate 37 (c) & (d)

Cells solitary or rarely united into short chains by the long spines arising from the valve surface. Spines long and in contrast to Odontella regia and Odontella sinensis located close to the centre of the valve surface. Valve processes slender, arising inside the valve margin, and directed outward.

Plate 37: Odontella longicruris (a) & (b); O. mobiliensis (c); (d). O. regia (d), dividing: O. regia (e), (f), (g) & (h); O. sinensis; (i), (j), (k), (l) & (m).

Two large spines about the same distance from each other arise from each end and directed obliquely outward. Cells contain numerous granular, plate-like chromatophores. Valves weakly silicified; valve areolation fine with 14–16 areolae in 10 µm. Centrally positioned nucleus usually visible in broad girdle view.

Odontella regia (Schultze) Simonsen 1974 (Plate 37 (d), (e), (f), (g) & (h) [Denticella regia Schultze 1859]

[Biddulphia regia (Schultze) Ostenfeld 1908]

Cells usually solitary but rarely united into short chains through the long spines. Valve view quadrangular with the four ends terminated by slender processes arising from the margins and directed diagonally outward. Two long large spines arise nearer the processes and directed obliquely outward. Cells neritic, commonly found in the lower reaches of the estuaries.

Odontella sinensis (Greville) Grunow 1884 (Plate 37: (i), (j), (k), (l), & (m) [Biddulphia sinensis Greville 1866]

Cells slender, longer than broad; occur singly or in chains when joined together by spines. Valve view narrow with ends produced into short slender processes slightly directed outward. Two long spines inserted and directed obliquely outward. The valve surface which is weakly siliceous is divided into a number of segments. Chromatophores numerous and discoid. Cells restricted in distribution to the lower reaches of the estuaries.

Genus Pleurosira (G. Meneghini) Trevisan 1848

Cells have large orbicular valves with 2–4 prominent ocelli, number depending on salinity. The ocelli secret mucopolysaccaride pads that join cells together in large, zigzag colonies. A single rimoportula is positioned near the centre of the valve face. Colonies form filaments that are visible in streams. Pleurosira is widely distributed in naturally saline waters and polluted waters. In older literature it was reported as a Biddulphia or Cerataulus.

Pleurosira laevis (Ehrenberg) Compere 1982 (Plate 38) [Biddulphia laevis Ehrenberg 1843]

Cells solitary, quadrangular in girdle view, with slight sub-conical processes, but sometimes in filaments. Valves circular to elliptical and 65–120 μm in diameter. Two ocelli positioned opposite one another. In both valve and girdle views, cells divided into three distinct segments; two to three rimoportulae present, each surrounded with a small hyaline area. Valve surface punctuate; spinules present across valve face and at the margin. Restricted to brackish waters of low salinities.

Plate 38: Pleurosira laevis (a) & (b) LM; (c) & (d) HD; (e) SEM

Genus Schuettia De Toni 1894

Cells triangular and similar to Triceratium in valve view, but markedly different in having concave sides. Currently regarded as a synonym of Actinoptychus.

Schuettia annulata (Wallich) De Toni (Plate 39)

Species originally described as Triceratium by Wallich on account of its triangular outline. Valves triangular with broad rounded apices and slightly concave sides. The apices are equipped with rows of fine pores from which arise three darker lines or “faults” in the valve surface. These “faults” or steps give an undulating appearance to the valve surface.

Plate 39 Shuetta annulata (a) LM, (b) HD, (c) SEM

The surfaces are not curved as in Actinoptychus but somewhat wedge-shaped. The punctae of the valve are arranged in concentric rings, which correspond to a series of ridges leaving sub- hyaline areas. Diameter, 40–90 µm.

Genus Triceratium Ehrenberg 1839

Cells free-living or attached; usually triangular in shape (valve view) and narrowly oblong in girdle view with elevated corners and a slightly convex centre. Valves triangular or sometimes square, shallow, often ornamented with simple or branched spines. Areolae loculate, opening externally via large foramina. Corner elevations present ending in ocelli.

Triceratium favus Ehrenberg 1840 (40)

Cells solitary, box-shaped in girdle view with a triangular cross-section and normally short pervalvar axis. Valve edges straight or slightly convex with rounded corners. Processes (ocelli) situated at each angle. Valve area between processes flat or slightly arched showing large regularly arranged hexagonal areolae arranged parallel to the valve margin. Chromatophores numerous, small and densely packed granules giving live cells a dark colour. Species widely distributed in coastal marine and brackish water environments.

Edge length, 115–120 µm.

Plate 40: Triceratium favus (a) & (b) Valve view, LM & HD respectively; (c) girdle view, HD

11.3.2Order PENNALES

Suborder ARAPHIDINEAE

Family DIATOMACEAE Dumortier 1822

Cells united into stellate colonies; intercalary bands, septa and costae absent; valves linear, with inflated ends, finely transversely striated; valve and girdle views symmetrical; pseudoraphe indistinct; chromatophores two to several somewhat lobed plates.

Genus Asterionella Hassal 1850

Cells rod-like with distinctly dissimilar ends, united into start-like or spiral colonies in which the cells hang together only by the thicker ends.

Asterionellopsis glacialis (Castrane) Round 1990 (41)

[Asterionella japonica Cleve ex Gran 1908]

Cells needle-shaped and arranged in star-like and helical colonial chains. In girdle view, cells have a narrow and elongated neck with a broad triangular base. Adjacent cells are attached by the valve face of the base and therefore usually appear in girdle view. In valve view, cells are rod-like with dissimilar apices, one of which is broadly enlarged, triangular and flattened with lobed base.

Plate 41: Asterionella japonica (a) LM; (b) HD; (c) SEM

Cells yellow brown in colour (Guiry 2012) and usually hang together only at the enlarged ends. Valve with a medium pseudoraphe. Length between 100–150 µm, width of enlarged base, 8–12 µm.

Genus Fragillaria Lyngbye 1819

Fragillaria is a genus of freshwater and saltwater diatoms. Ribbon-like chains of colonial cells attached by the whole of the valve faces; girdle view rectangular and rod-like; in valve view frustules rectangular to lanceolate, more or less bulging in the middle. Valves flat, without or with a rudimentary pseudoraphe, bilaterally symmetrical. Occurs in both freshwater and saltwater habitats. Found as plankton and benthic species. Some species are bloom forming diatoms in eutrophic lakes.

Fragillaria construens (Ehr.) Grunow 1862 (Plate 42 a, b & c)

Common diatom found in a variety of aquatic habitats worldwide mainly in brackish waters of moderate salinity. Found in three varieties in marine, brackish and freshwater environments.

Plate 42: Fragillaria construens (different forms) (a), (b), (c) & (d) LM Fragillaria javanica, (e) LM

Fragillaria javanica Hustedt 1938 (Plate 42 (e)

Fragillaria javanica is a type species of a widely reported species with tropical distribution. The taxon is each characterised by areolae covered externally with a rota, well-developed, simple apical porefields composed of rounded poroids located on both valve apices. These features are all shared with species currently ascribed to Fragilariforma with spine shape and orientation, and girdle having two rows of areolae, along with valvocopulae.

Genus Synedra Ehrenberg 1830

Cells narrow and much elongated, solitary or in tufted, fan-shaped or radiating colonies, free- floating or epiphytic, sessile or stalked; valves linear to lanceolate, straight or sometimes curved, with poles attenuated or not, often capitate; transverse striation lateral to a conspicuous narrow pseudoraphe. Intercalary bands and septa absent, girdle band consequently narrow linear. Chromatophores, variable numerous small granules or two large plates. Most of the species belonging to the genus are freshwater.

Synedra acus Kutz. (Plate 43 a, b, & c)

Valve lanceolate, tapering to rounded, or slightly capitate apices. Pseudoraphe narrow, becoming a little wider towards the middle of the valve. Central area distinct, a little longer than broad. Striae parallel, 10–15 in 10 µm. Length, 280–321 µm; breadth 4.8–7.5 µm.

Synedra superba Kutzing 1844 (Plate 43 d)

Valves broadly linear and slightly attenuated from the centre towards the rounded apices. Striae quite distinct and arranged transversely in three longitudinal rows. Freshwater in distribution. Length 150–300 µm.

Synedra ulna (Nitzsch) Ehrenberg 1836 (Plate 43 (e) & f)

[Bacillaria ulna Nitzsch 1817]

Cells solitary and relatively short, linear in girdle view, with widened extremities. Valves linear to linear-lanceolate, gradually attenuated towards the ends, with broadly rounded poles. Transverse striations 8–12 in 10 µm, finely punctuate; pseudoraphe narrowly linear, usually with central area absent.

Plate 43: Synedra acus (a), (b), & (c); S. superba (d); S. ulna (e) & (f)

Genus Tabellaria Ehrenberg 1839

Cells tubular in girdle view, united usually into zigzag chains, sometimes into stellate colonies, with four to several intercalary bands per cell; valves elongate, bilaterally symmetrical, generally inflated at the poles and in the middle; narrow pseudoraphe; chromatophores numerous small discs. Ecologically found in freshwaters

Tabellaria fenestrata (Lyngbye) Kûtzing 1844 (Plate 44, a & b

Cells narrowly elongate, forming star-like zigzag chains. Valve surfaces slightly inflated in the mid-region and with finely punctuate striations. The striae are parallel and alternate. The axial is narrow and linear. Presence of a pseudoraphe. The cells are joined in colonies that form a long, straight chain. The frustules are rectangular in girdle view and with breadth ratio in girdle vie as great as 8:1. The species can be planktonic or growing attached to vegetation or other hard substrates.

Tabellaria flocculosa (Rothe) Kutzing 1844 (Plate 44, c & d)

Cells in girdle view short-elongate or rectangular forming zigzag chains. Valves are linear with inflation in the centre of the valve and with slightly capitate apices. The median inflation of the valve is wider than the apices. The central area is small and rhombic. Cells sometimes asymmetrical in valve view; valve with finely punctuate striations; inflated markedly in the middle and slightly or not at all at the poles; presence of a narrow pseudoraphe. Length to breadth ratio of frustules not more than 2:1.

Plate 44: Tabellaria fenestra (a) & (b) LM; Tabellaria floculosa (c) & (d) LM

Genus Thalassionema Grunow ex Hustedt 1932 Emended description (Hallegraeff 1986)

Long (10–400 µm) needle-shaped frustules, united into stellate or zigzag colonies. Valves furnished with uniquely structured marginal areolae, appearing as a row of open depressions on the edge of the valve face. Axial area (pseudoraphe) and girdle bands without areolation. Habitat, marine plankton, widespread in distribution.

Thalassionema frauenfeldii (Grun.) Hallegraeff, 1986 (45 a, b, c, & d)

[Asterionella frauenfeldi (Grun.) Grunow 1863],

[Thalassiothrix fruenfeldi (Grunow)

Cells rod-shaped, straight or slightly bent and united often into stellate colonies by gelatinous cushion on the end of the cells. Cells relatively long, 90–200 µm and 4–6 µm wide. Valve surface with short marginal striae; chromatophores in numerous small granules. Neritic and oceanic in distribution.

Thalasionema nitzschiodes (Grunow) Hustedt 1932 (Plate 45 f & g) [Synedra nitzschiodes (Grunow) 1862]

Frustules united into star-like zigzag colonies, straight and linear or slightly curved. In girdle view elongated-rectangular. Valves narrow linear with parallel sides and bluntly rounded apices. Small marginal spines present in girdle view. Neritic and ubiquitous in distribution in shallow coastal ocean waters, except in Polar Regions.

Plate 45: Thalasionema fruenfeldii (a) & (b) LM, (c), (d) & (e) SEM Thalasionema nitzschiodes (f) LM, (g) HD

Family EUNOTIACEAE Kützing 1844

Genus Desmogonium Ehrenberg 1848

Frustules rectangular in girdle view; often forming more or less zigzag filaments. Valves slightly curved, symmetrical to the transverse axis. Terminal nodules distinct on the ventral margin and variable in size. Jelly pore usually evident at both ends of the valve. This genus is closely related to the genus Eunotia from which it was derived and mainly differs in its manner of growth and presence of spines on both margins of the valve. Commonly found in Desmogonium rabenhorstianum var. elongatum R. M. Patrick 1998 (Plate 46) [Formerly Eunotia rabenhorstianum var. elongatum R. M. Patrick 1940.]

Frustules in girdle view wedge-shaped, forming curved or circular filaments. Often arranged in zigzag filaments. Valve narrowly linear, slightly curved with large swollen ends, which are rounded to slightly wedge-shaped. Terminal nodules distinct on the ventral margin of the swollen end. Jelly pores apparent. Striae distinctly punctuate and fine. Marginal spines are evident on both margins of valve. This variety is distinguished by its great length and broadly swollen, rounded ends. Very common in the tropics and strongly in acid waters.

Plate 46: Desmogonium rabenhorstianum var. elongatum LM

Genus Eunotia Ehrenberg 1837

Frustules rectangular in girdle view, both girdles and valves strongly ornamented, usually with intercalary bands, free-floating or epiphytic, solitary valve or united into chains; valves arcuate, with similar poles but dissimilar margins; intercalary bands usually present; two somewhat laminate chromatophores, without pyernoids. Plate 56 illustrates a display of different mixture of Eunotia spp.

Plate 47: Mixture of various Eunotia spp.

Eunotia asterionelloides Hustedt 1952 (Plate 48)

Cells rectangular in girdle view and united into chains; valve view slightly curved with a convex dorsal side and a concave ventral side. Apices sub-capitate.

greater than at the centre. Terminal nodules distinct. Through this species the genus Eunotia seems to be related to Desmogonium.

Plate 48: Eunotia asterionelloides (a) & (b) LM; (c) HD; (d) & (e) SEM

Eunotia flexuosa Kutzing 1849 (Plate 50) [Synedra biceps W. Smith 1853]

[Eunotia bicapitata Grun. in Van Heurck 1881]

Frustules linear in girdle view. In valve view also linear and slightly arched; somewhat swollen to form more or less capitates ends. Width of the valves at the ends usually a little greater than at the centre. Terminal nodules distinct. Through this species the genus Eunotia seems to be related to Desmogonium.

Plate 49: Eunotia flexosa

Eunotia garusica Cholnoky 1952 [Plate 50 (1a), (1b), (1c), & (1d)]

Frustule/valve three times as long as broad; dorsal margin triundulate and ventral margin with a bulge in the middle. Valve 26–39 µm; width 8–12 µm. 11–12 striae in 10 µm.

Eunotia monodon Ehr. var. maior (W. Smith) Hustedt [Plate 50 (2a) & (2b)]

Valve 254 x 16 µm, 9 striae in 10 µm, with several slight undulations on the dorsal margins. Ventral margin concave, with a spine at the apex.

Plate 50: Eunotia garisuca (1a), (1b), (1c) & (1d); Eunotia monodon var. maior (2a) & (2b); Eunotia monodon var. tropica (3a), (3b) & (3c); Eunotia naegelii (4a); Eunotia papilio (5a)

Eunotia monodon Ehr. var. tropica Husted [Plate 50 (3a), (3b & (3c)]

Valves arcuate shaped, five times as long as broad. 4–8 undulate (humps) on the wavy dorsal margin; concave on the ventral margin and slightly convex on the dorsal margin. Measurement: length, 49.5–163 µm; width, 10–13 µm. Apices broadly rounded (in larger specimens) or tapered (in smaller specimens). Striae punctuate 11–14 in 10 µm (Gluscchenko and Kulikovskiy, 2017). Kadiri and Opute (2003) reported dimensions of 76–79 x 15–21 µm and 14 striae in 10 µm. Eunotia naigelii Migula 1907 [Plate 50 (4a)]

Valves moderately arched with convex prominent dorsal margins and concave ventral margins. Length, 73–155 µm; width, 2.5–2.6 µm. Apices slightly inflated, sub-capitate, and slightly recurved towards the dorsal margins. Striae parallel all along the valves; 19–23 in 10 µm (Gluschenko and Kulikocskiy, 2017).

Eunotia papilio Ehr. [Plate 50 (5a)]

Valve butterfly shaped, 1⅟2 times as long as broad, with dorsal margin strongly bi-undulate and ventral margin deeply concave. Measurements: Length, 29- 30 µm, Width, 18–20 µm; striae 15–17 in 10 µm.

Family NAVICULACEAE Kutz. 1844

Genus Amphiprora Ehrenberg 1843

Cells solitary, free-floating, or sessile and adhering to objects by a gelatinous envelope, naviculoid in valve view, hour-glass shape in girdle view with a sigmoid girdle; sigmoid raphe in outer margin of keel with small central and polar nodules; chromatophores one, sometimes two.

Amphiprora alata (Ehrenberg) Kutzing 1844 (Plate 51)

Cells, linear-elliptic to linear lanceolate with slightly concave sides and apiculate apices. Girdle view highly arched bilobate keels. The keels strongly torsioned, occasionally with only one lobe in focus at one time. In complete frustules in girdle view, diagonally opposing lobes lie at approximately the same level of focus. Lobes flattened in large specimens and more rounded in smaller specimens. Several girdle bands are present. Junction line between valve and keel marked by an irregular series of dark spots. In valve view these spots can be seen as thickened siliceous ribs that frame a series of prominent swellings along the junction line.

Plate 51: Amphiprora alata (valve view) LM

The swellings are approximately equal in size. Striae on the valve face continue onto the keel. Areolae on the valve face very fine and number 26–30 in 10 µm. Areolae on the keel much more prominent, 12–15 in 10 µm within.

Genus Amphora Ehrenberg 1840

Cells usually sessile with concave faces attached in girdle view, broadly elliptic in outline, with truncate ends; valves lunate, longitudinally asymmetric, transversely striate; raphe gibbous, with its central nodule close to the concave margin; chromatophores single, 2–4 µm.

Amphora ovalis Kützing 1844 (Plate 52)

[Navicula ovalis Ehrenberg 1832]

[Frustlia ovalis Kützing 1833]

Cells in girdle view broadly elliptic with truncate apices. Valve lunate with blunt poles, ventrally concave and dorsally convex; raphe gibbous. Dorsal striae interrupted at the middle by a circular or irregular hyaline area parallel in arrangement.

Plate 52: Amphora ovalis LM

Genus Brachysira Kutzing 1836

Valves of Brachysira are linear to linear-lanceolate in outline. The ends of the valves, or apices, may be rounded to protracted. In general, the valves are symmetric to the apical axis, although some specimens may have a slight, to strong, asymmetry to the transapical axis. The striae are finely punctate, and form longitudinal undulations. The raphe is straight and the axial area is narrow. In the SEM, an elevated siliceous ridge separating the valve face and mantle on the external valve surface is visible. Cells possess a single plastid. Brachysira have been found to grow singly and unattached, or it may grow at the ends of mucilaginous stalks. Species within the genus are broadly distributed in a range of trophic states, with individual species characteristic of oligotrophic to dystrophic waters. Cell abundance is especially high in low conductivity and acidic waters. The genus is primarily benthic but may also be found in lake plankton, where cells may become entrained.

Brachysira serians (Brebisson) Round & Mann 1981 (Plate 53)

Valves lanceolate

Striae slightly radially parallel

Central area asymmetrically rounded

Raphe straight at distal end.

Brachysira serians (Breb.) Courtsey Round & D. G. Mann 1981

Plate 53: Brachysira serians (a) x 7,000; (b) x 10,000

The raphe is positioned between two external, longitudinal ribs. The raphe is straight with straight proximal fissures and T-shaped distal fissures. Areolae are elongated rectangular slits with rounded ends, oriented to the transapical axis. Spaces between the areolae give the appearance of longitudinal undulations. The mantle possesses a single row of elongated areolae. Valve length 35–38 µm, width 8 µm; 22–25 striae in 10 µm. Species found in freshwater water plankton in acidic water bodies. Tropical species previously reported in Sierra-Leone (Woodhead & Tweed, 1958; Carter & Denny, 1982), Senegal and Zaire (Woodhead & Tweed, 1958) and Lake Tanganyika (Cocquyt et al., 1993).

Genus Cymbella C. A. Agardh 1830

The valves of Cymbella are slightly to strongly asymmetric to the apical axis. Valves are symmetric to the transapical axis. The terminal raphe fissures are deflected to the dorsal side, an important diagnostic feature. Apical pore fields are present at both poles. Striae are uniseriate. One or more stigmata may be present. If a stigma or stigmata are present, they are located on the ventral side of the central area. Internally, the stigmata are convoluted internal occlusions. Also internally, the proximal raphe may be continuous across central area. Cymbella cells grow predominately in benthic habitats, and often produce mucilaginous stalks that are secreted through the apical porefield.

Cymbella microcephala Grun. (Plate 54)

Valve 35–38 µm long, 22–25 µm wide; narrow, elliptic to slightly dorsiventral; raphe straight and deflected in the same direction at the central area. Carter and Denny (1982) observed forms of C. microcephala that are somewhat more linear than normal. This species has been designated as not actually endangered and is tolerant to a wide range of habitats, from oligotrophic to eutrophic waters without discernable preference (Lange-Bertlot and Rumrich, 2000).

00Valves slightly to strongly asymmetric to the apical axis

Distal raphe ends deflected dorsally

Apical porefields present

Stigmata if present, located on the ventral side.

Courtesy: Pat Kociolek (2011)

Plate 54: Cymbella microcephala (a) x 3,000, (b) x 4,500

Genus Encyonema Kutzing 1833

The taxonomy of Encyonema has undergone many changes. Until the end of last century, representatives of Encyonema were treated in the genus Cymbellla C. Agardh since both groups have dorsiventral valves. In 1990, the genus Encyonema was resurrected by Round et al, and included in the family Naviculaceae Kutz., together with other genera such as Cymbella and Gomphonema. Subsequently Krammer (1997a, 1997b) carried out an extensive revision of Encyonema that culminated in a series of new species and combinations.

Encyonema prostratum Kutzing 1834 (plate 55) (Encyonema liebleinii) (Agardh) Silva et al. 2013

Commonly colonial and grows in mucilage tubes. Found in freshwater communities and common in lentic systems. Valves semi-lanceolate and dorsiventral. Dorsal margin of valve highly arched; ventral margin slightly convex. Valve apices broadly rounded; rostrate in larger valves and usually ventrally bent. A narrow, straight axial area runs the length of the valve. Central area circular and raphe is simple. Striae punctuate. Dorsal striae radiate throughout; ventral striae radiate at the valve centre becoming parallel toward the apices. Distal raphe fissures terminate before valve margin. Length 40–65 µm; width range 16–23 µm; 7–10 striae in 10 µm. Areolar density 16–20 in 10 µm.

Plate 55: Encyonema prostratum LM

Genus Diploneis (Ehrenberg) Cleve 1894

A genus belonging to the family Diploneidaceae. Cells are free and solitary. Valves linear elliptical or more or less constricted in the mid region; central nodule thickened and H-shaped with a broad siliceous rib. Apical axis bisected by raphe. Habitat both freshwater and marine and has cosmopolitan distribution.

Diploneis smithii (Breb) Cleve var. rhombica Mereschkowsky, 1902 (Plate 56)

Cells solitary, valves broadly linear-elliptical with broadly rounded apices. Central area relatively small, thickened and forming an irregular, rounded to rectangular hyaline area. Longitudinal canals on each side crossed by striae. Striae distinctly doubly punctate, radiate, 5–12 in 10 µm. Length 25–200 µm; breadth 15–75 µm.

Plate 56: Diploneis smithii (a) LM, (b) SEM

Genus Frustulia Rabenhorst 1853

Cells solitary and free-floating or sessile and enclosed in a gelatinous envelope, sometimes in a gelatinous tube; in valve view linear-elliptic to rhombo-lanceolate; central nodule longitudinally elongate, prolonged toward each pole into two parallel ribs apically united with the polar nodule; two chromatophores sometimes longitudinally incised.

Frustulia rhomboides (Ehrenberg) De Toni 1891 (Plate 57) [Navicula rhomboides Ehrenberg 1843]

Cells solitary, free-floating; valve rhombic-lanceolate, narrowing sharply to rounded ends; central nodule longitudinally elongated.

Plate 57: Frustulia rhomboides (a) LM; (b) SEM

Frustulia interposita (Lewis) De Toni 1891 (Plate 58)

Valve linear-elliptical with broadly rounded ends. Central area slightly wider than the axial area. Transverse striae parallel, distinct; 20–22 in 10 µm; longitudinal striae parallel, 16–20 in 10 µm. Length, 100–130 µm; breadth, 23–27 µm. This species was among those described by Mills (1932) in his diatom collections from Warri River.

Plate 58: Frustulia interposita LM

Genus Gyrosigma Hassal 1845

Cells solitary and free-floating, sometimes in gelatinous tubes, elliptic-lanceolate in girdle view, intercalary bands and septa absent; valves sigmoid, usually gradually attenuate; rarely with nearly straight sides to broadly rounded poles; raphe sigmoid, with central and polar nodules; transverse striations crossing longitudinal striations at right angles; two chromatophores, regularly or irregularly shaped plates, generally with numerous pyrenoids.

Gyrosigma balticum (Ehrenberg) Rabenh. 1853 (Plate 59) [Navicula baltica Ehrenberg 1834]

Valve linear with parallel margins, slightly sigmoid with bluntly rounded sub-conical ends; axial area and raphe undulate and eccentric; valve surface striate; striae distinctly punctuate; punctae arranged in longitudinal and transverse lines crossing each other at an angle of 90o.

Plate 59: Gyrosigma balticum (a) LM; (b) HD; (c) SEM of mid region of cell

Genus Navicula Bory de Saint-Vincent 1822

Cells usually free, motile. In planktonic species usually united into ribbon-like chains. Valve linear to elliptical, with rounded, capitate or rostrate ends. Axial and central area usually distinct. Striae or costae parallel or radiate, finely or coarsely punctate, lineate or apparently smooth. Both valves with raphe and central nodule but without keel. Chromatophores two, in bands, one on each zone, sometimes extending over the valves.

Navicula radiosa Kutz 1844 (Plate 60)

The valves are narrow and lanceolate with acutely produced rounded ends. The central area is rhombic. The striae are strongly radiate, bent in the valve centre and convergent near the poles, 18 striae in 10 µm. Lineolae numbers 28–32 in 10 μm. This species has been widely reported in Nigeria from Warri/Forcados estuary (Opute, 1991), Lagos lagoon (Nwankwo, 1988) Lake Chad (Iltis, 1972; Compere, 1975) and in Africa from Sierra Leone, Burkina Fasso, Niger, Republic du Benin, Togo, Angola (Woodhead & Tweed, 1958); Zaire (Woodhead & Tweed, 1958; 1960), and in Lakes Tanganyika, Nyasa and Victoria (Cocquyt et al, 1993).

00Valves narrow lanceolate, 52–105 µm long.

Valves 8.8- 11.2 µm wide

Apices acutely rounded.

Central area rhomboic.

Central area strongly radiate.

Navicula radiosa Kutzing 1844 Credit: Marina Potapova

Plate 60: Navicula radiosa SEM

Genus Pinnularia Ehrenberg 1843

Cells solitary and free-floating, rarely in short filaments, symmetric, rectangular in girdle view, girdles smooth, intercalary bands absent; valves usually with straight sides, sometimes medianly inflated or undulate, generally with broadened rounded poles; axial field usually broad, expanded both polarly and medianly, with complicated straight or sigmoid raphe; costae, with internal openings, smooth, radial or transverse, with two longitudinal lines; chromatophores two, laminate, usually with pyrenoids. Pinnularia contains a large number of species and often abundant in freshwater of low conductance, slightly acidic waters.

Pinnularia acrosphaeria W. H. Smith 1853 (Plate 61)

[Navicula nobilis Ehrenberg 1840]

Valve linear, slightly swollen in the middle portion and a little wider at the broadly rounded sub-capitate apices. Raphe lateral, outer fissures straight. Valve surface has a mottled appearance. Axial area occupies most of the length and is one-fourth to one-third the breadth of the valve. Central area rounded; raphe complex and undulate; terminal fissures distinct “question mark” shaped. Proximal raphe ends are weakly expanded, deflected to one side, and closely spaced. Transverse striations weakly radiate at the valve centre, parallel throughout the rest of the valve, and polarly convergent and crossed by a wide longitudinal band. Mainly tropical in distribution, but also widespread in temperate regions.

Plate 61: Pinnularia acrosphaeria LM

Pinnularia hartleyana Greville 1865 (Plate 62)

Freshwater species reported by Mills in 1932 from samples collected from the Warri River, South Nigeria. Specimens have the central nodule but fascia not central and nearer to one end of the valve than the other.

Plate 62: Pinnularia hartleyana LM

Pinnularia hartleyana var. attenuata F. W. Mills 1932 (Plate 63)

This variety was first reported by F. W. Mills in samples collected from the Warri River in 1932. Axial area linear, one-third as broad as the valve. Length 305–310 µm; width 35 µm

Plate 63: Pinnularia hartleyana var. attenuata LM

Pinnularia hartleyana var. pulchella Greville 1865 (Plate 64)

Cells longer than the type specimen, more gibbous in the middle and at the ends of the valve surface. The costae are also much finer. Axial area at least one-third as broad as the valve. Cells variable in size, found mostly between freshwater and estuarine parts of the river.

Plate 64: Pinnularia hartleyana var. pulchella LM

This taxon was reported by Mills as a new variety in samples collected from the Warri vicinity in 1932. Width 26–33 µm, length 205–280 µm.

Pinnularia nigritiensis F. W. Mills 1932 (Plate 65)

Valves linear to elliptic-linear which are slightly inflated narrowing to some extent towards broadly rounded ends. Central area lanceolate expanding asymmetrically around the central nodule. Terminal nodules broad. Terminal nodules broad. Raphe complex, somewhat undulate; Transverse striations medianly lightly radial, polarly convergent, crossed by a wide longitudinal band through the middle. New robust species first reported by F. W. Mills 1932 from diatoms from Warri, South Nigeria. Length 128–130 µm, width 22–24 µm.

Plate 65: Pinnularia nigritiensis LM

Pinnularia rivularis Hustedt 1935 (Plate 66)

Valve linear, slightly dilated in the middle region, but much wider at the poles which are cuneately rounded. Axial area narrow, about one-fourth of the cell diameter. Central area extends to the margins as a large transverse fascia. Raphe branches filiform, central fissures closely located and terminates as a distinct “question mark” shape. Striae in the central area radiate towards the middle, but convergent towards the apices. This taxon is very similar to the type described by Mills as Pinnularia confragosa in his collections from Warri River in 1932.

Plate 66: Pinnularia rivularis LM

Pinnularia socialis var. debsii (Hustedt) Krammer, 2000 (Plate 67)

Species rare and remarkable. Cells mostly united usually in threes or fours, seldom less or more. Valve broadly linear with parallel margins obtusely rounded at the ends. Axial area occupies between one fourth and one third the breadth of the valve and is somewhat wider towards the central area.

Plate 67: Pinnularia socialis var. debsii (a) & (b) Three and four celled LM; (c) HD

Raphe filamentous and characteristic with more or less “bayonet” shaped terminal fissures. Striae mostly parallel or radiate towards the middle part of the valve and slightly convergent towards the apices. This taxon appears to be the same described by Mills (1932) as Pinnularia Debsii Hustedt, 1926 from the diatoms collected from the same locality (Warri River).

Pinnularia subcapitata Gregory 1856 (Plate 68)

Valves linear with almost straight or very slightly convex margin and sub-capitate ends, rostrate ends in smaller valves. Isopolar and bilaterally symmetrical. Striae parallel, rarely slightly radiate in central part of valve, convergent towards the ends. Raphe slightly curved with expanded proximal endings deflected to one side; terminal fissures curved and terminating on the mantle.

Plate 68: Pinnularia subcapitata SEM magnifications Genus

Pleurosigma Wm. Smith 1852

Cells solitary, elliptic-lanceolate in girdle view, intercalary bands and septa usually absent; valves sigmoid, gradually tapering to rounded or sub-acute ends; raphe sigmoid, with small central and polar nodules; axial area narrow; central area usually round; striations in three series; one perpendicular to the middle line of the valve, the other two oblique to the middle line; chromatophores two, four or many regular or irregular plates.

Pleurosigma angulatum (Quek.) W. Smith 1852 (Plate 69) [Navicula angulatum Quek. 1848]

Cells sigmoid, rhombic-lanceolate; slightly to distinctly medianly angular in the middle, tapering rather sharply to acutely rounded ends. Valve surface relatively flat. Axial area and raphe sigmoid becoming eccentric towards the ends. Central area small, rhombic; transverse and diagonal striations about the same in number 15–18 in 10 µm and crossing at an angle of about 60o.

Plate 69: Pleurosigma angulatum (a) LM; (b) HD

Pleurosigma australe Grunow 1868 (Plate 70)

Valve moderately sigmoid, narrow-lanceolate tapering to acutely rounded ends. Axial area and raphe slightly eccentric. Central area circular or somewhat rhombic. Transverse striae finer than oblique striae which cross each other at an angle of 60o near the centre. Striae and punctae coarse in the middle region of the valve, becoming finer at the ends.

Plate 70: Pleurosigma australe LM

Pleurosigma decorum W. Smith 1853 (Plate 71)

Valve lanceolate, sigmoid with attenuated sub-acute to obtuse ends. Axial area almost indistinct. Raphe eccentric, becoming marginal towards the poles. Central area rounded.

Plate 71: Pleurosigma decorum (a) LM; (b) HD

Pleurosigma delicatulum W. Smith 1852 (Plate 72)

Valve sigmoid, narrow-lanceolate; gradually tapering to acutely rounded apices. Axial area and raphe central in the main portion of the valve, becoming eccentric towards the ends; central area elliptical. Transverse and oblique striae roughly of the same number and crossing each other at an angle of between 56–60o.

Plate 72: Pleurosigma delicatulum LM

Pleurosigma formosum W. Smith 1852 (Plate 73)

Valves elongate, linear-lanceolate, slightly sigmoid with sub-acute apices. Axial area indistinct. Raphe strongly sigmoid, eccentric and marginal towards the poles; central area and nodules small. Striae coarse, punctae arranged in oblique and transverse lines crossing each other at about 55o.

Plate 73: Pleurosigma formosum (a) LM; (b) HD

Family Nitzschiaceae Grunow 1860 Genus Bacillaria Gmelin in Linnaeus 1778

Cells rod-like, the shape of wooden matches, united in moveable bands, each cell moving on its neighbour. Cells rectangular in girdle view (when in colonies), and lanceolate in valve view. Raphe slightly keeled and runs from pole to pole. Nucleus located centrally, with two large plate-like chromatophores present, one on each end of the cell.

Bacillaria paxillifer (O. F. Mueller) Hendey 1951 (Plate 74) [Vibrio paxillifer Mueller 1786]

[Nitzschia paxillifer (Mueller) Heib. 1863]

[Nitzschia paradoxa (Gmelin) Grun. in Cleve et Grun. 1880]

Frustules aggregated together into moveable colonies, displaying a characteristic sliding movement along one another. Rectangular in girdle view, linear-lanceolate in valve view with acute apices. Valve surface with parallel transverse striae. Chromatophores small and numerous. Commonly distributed in freshwater habitats.

Plate 74: Bacillaria paxillifer (a) LM; (b) HD

Genus Hantzschia Grunow 1877

Hantzschia is a genus of diatoms belonging to the family Bacillariaceae. The genus was first described by Albert Grunow in 1877. Species include Hantzschia amphioxus, Hantzschia spectabilis and Hantzschia virgata.

Hantzschia spectabilis (Ehrenberg) Hustedt, 1959 (Plate 75)

Previously described as Synedra spectabilis Ehrenberg, 1841 and Hantzschia vivax (W.Smith) Tempere, 1908. Cosmopolitan, found in marine, brackish, freshwater, and terrestrial environments. Characterised by having valves asymmetrical to the apical axix; markedly dorsiventral, with an eccentric raphe on the ventral side.

Plate 75: Hantzschia spectabilis LM

Genus Nitzschia Hassall 1850

Nitzschia is a common pennate marine and freshwater diatom. In the scientific literature, this genus, named after Christian Ludwig Nitzsch, is sometimes termed Nitzschia, and it has many species described, which all have a similar morphology. Cells spindle-shaped, single or united into colonies. Valves keeled, the keel including a concealed raphe, usually diagonally opposite, either central or eccentric. Striae transverse, punctuate. No central nodule. Chromatophores two bands placed transversely upon one zone. A pyrenoid sometimes found in centre of chromatophore.

Nitzschia acicularis (Kutz.) W. Smith 1853 (Plate 76)

Cells solitary. Frustules isopolar, bilaterally symmetrical. Cells usually lie in valve view. Valves bilaterally symmetrical, elongate, with a linear to linear-lanceolate shape. Striae very fine, not visible in low magnification; 60–72 in 10 µm. Raphe also not visible in low magnification.

Plate 76: Nitzschia acicularis LM

Nitzschia obtusa (Krammer and Lange-Bertalot, 1988 (Plate 77)

Formerly described as Nitzschia kurzeana Ehrenberg 1873. Valves linear in girdle view, with distal ends curved to opposite ends to form a slight to moderate sigmoid shape. Terminal ends bluntly rounded. Raphe located in a canal and positioned near the valve margin, slightly indented toward the central valve at mid-valve. Valves 120–200 µm long; 6–12 µm broad. Keel strongly eccentric, curving onto the valve face at the centre, with a distinct central nodule. Keel punctae irregularly spaced, 6.5–8 in 10 µm. The terminal raphe fissures distinctly recurved. Striae 25–40 in 10 µm.

Plate 77: Nitzschia obtusa (a) LM; (b) HD

Nitzschia obtusa W. Smith var. scalpelliformis Grunow 1881 (Plate 78)

Specimens vary in length from 90 to 117 µm in length and are about 10µm wide. The apices are bluntly pointed and slightly bent. The structure shows a hyaline margin on one side and a double row of large rectangular areolae arranged alternatively and appearing like a scapel. First reported by Hendey (1957) as occurring in Sierra Leone from the collections of Marine Diatoms from some West African Ports.

Plate 78: Nitzschia obtusa var. scalpelliformis LM

Nitzschia seriata Cleve 1883 (Plate 79)

Cells spindle-shaped with more or less pointed to moderately rounded ends. United into stiff, hair-like chains by the overlapping points of the cells. Chains motile as a whole. Length of valves 80–140 µm; width 6.2–8 µm. Keel punctae indistinct, about the same number as the striae. Striae 14–19 in 10 µm, punctuate. Chromatophores two per cell, one on each side of the central nucleus. Neritic, widely distributed in the open seas and along the coast.

Cells spindle-shaped with pointed to rounded ends. United into stiff, hairlike chains by the overlapping points of the cells. Chains motile. Length of valves 80–140 µm; width 6–8 µm. Striae 14–19 in 10 µm, punctuate. Chromatophores two per cell, one on each side of the central nucleus. Species oceanic and neritic.

Plate 79: Nitzschia seriata LM

Nitzschia vermicularis (Kutz.) Hantzsch in Rabenhorst 1848–1850 (Plate 80)

Valves linear, slightly s-shaped in valve view. Margins parallel to slightly convex, tapering to small, angular apices. Length 90–120 µm, breadth 5–7 µm. Raphe excentric, keel puncta number 9–12 in10 µm. Central nodule distinct. Striae fine, 30–35 in 10 µm. Rare.

Plate 80: Nitzschia vermicularis LM Family

SURIRELLACEAE Kutzing 1844

Genus Stenopterobia Brebisson ex H. Van Heurck 1896

Stenopterobia is a small genus of freshwater diatoms in the family Surirellaceae found predominantly as motile forms in acidic, poorly buffered, and oligotrophic waters. Species are distinguished from the genus Surirella by the narrow and elongated shape of the frustules and the sigmoid configuration in valve view. Some species are straight and linear to linear- lanceolate in outline.

Stenopterobia pelagica Hustedt 1942 in Huber-Pestalozzi (Plate 81)

Valves narrow, straight, or sigmoid in outline. Raphe located within a canal along the valve margin. Canal raised above the valve, onto a keel. Freshwater species. Length 65–220 µm; width 6–7 µm. Striae 36 in 10 µm

Plate 81: Stenopterobia pelagica (a) LM; (b) HD

Stenopterobia rautenbachiae Cholnoky 1958 (Plate 82)

First described by Cholnoky (1957) as a new species. Valve and raphe system less complex and distinct from that of Surirella. Areolae capped, without internal coverings, striae multiseriate. Characteristics include externally valve face coverings and laterally opened girdle bands.

Plate 82: Stenopterobia rautenbachiae (a) LM; (b) SEM

Genus Surirella Turpin 1828

Cells of Surirella grow as single, isolated cells which appear in valve or girdle view; occasionally cells are spiralled. The frustules may be either isopolar or heteropolar. Isopolar valves with a definite longitudinal axis, but may be elliptical or even circular in shape, more often valves are linear, lanceolate or rhombic. Valves bilaterally symmetrical. Axial area is extremely narrow and is indistinguishable in low magnification. Raphe running around the whole perimeter of the valve and opening inwardly into a tubular canal (‘canal-raphe’) raised on a ridge or keel. One chromoplast per cell, consisting of two large plates, often lobed at their margins, connected by a narrow isthmus that lies at one end of the cell, or close to the nucleus in a sub-central position.

Surirella celebesiana Hustedt (1942) (Plate 83)

Cells slightly heteropolar and linear-elliptical in outline with cuneate narrowly rounded apices. Valves 70–82 µm long, 22–30 µm wide. Valves at the apex strongly convex. Wings vertical and not horizontally extended and terminate at the apices. Valve face finely striated with uniseriate to biserite striae, and approximately 55 areolar rows in 10 µm. Areolae visible in the median area.

Plate 83: Surirella celebesiana (a) LM; (b) SEM

Surirella engleri O Müller 1903 (Plate 84)

Valves linear with cuneate or somewhat protracted poles. Costae weakly developed, straight in the middle. Shows a continuous line of pseudoraphe. Pleura long linear with blunt poles, and rounded angles. Length from 150–250 µm, width: 27–38 µm. Also reported in the plankton from Lake Nyassa in East Africa by Hendey (1957)

Plate 84: Surirella engleri LM

Surirella fastuosa (Ehr.) Ehrenberg 1843 (Plate 85)

Cells usually oval, highly variable in shape. Valve faces highly ornate; has a circumferential raphe running around the cell on the keel at the point where the valve face and the mantle meet. The external raphe fissure opens into a raphe canal situated at the angle between mantle and valve face; raphe canal opens into the inside of the cell through perforate fibulate plate.

Plate 85: Surirella fastuosa LM

Surirella elegans Ehrenberg 1841 (Plate 86)

Freshwater diatoms, grows as single, isolated cells. Ends, heteropolar from valve view, cuneate from girdle view. Valve view ellipsoid, narrow and wide with bluntly rounded poles. In longer individuals ends may be cuneately narrowed. Wing, narrow with somewhat vague projection. Frustules, either isopolar or heteropolar. Raphe positioned along entire margin and located within a canal, which may be raised above valve surface. Cells highly silicified with spines and silica nodules on the valve surface. Found in lakes, ponds, rivers, thermal springs and swamps. Length 110- 400 µm; width 35–90 µm; wing canal 12–21 ribs in 100 µm.

Plate 86: Surirella elegans (a) & (b) HD; (c) & (d) LM; (e), (f) & (g) SEM

Surirella gemma (Ehrenberg) Kutzing 1844 (Plate 87)

Cells in valvar view elliptically ovate with the broader apex not bluntly rounded, but slightly produced giving a cunciform appearance.

Plate 87: Surirella gemma LM

Surirella ovalis Brebisson 1838 (Plate 88)

Valves extremely variable in size and outline, ovate, 24–56 µm long by 18–35 µm wide. The larger valves have cuneately rounded apices, while the smaller valves have two broadly rounded apices. The costae density, 14–17 µm with some raised above the others. The fibulae are marginal with density 5–6 in 10 µm. Krammer and Lang-Bertalot (1987) observation on the type material is the occurrence of a single portula on the mantle between the fibulae.

Plate 88: Surirrela ovalis

Surirella robusta Ehrenberg 1841(Plate 89)

Valve heteropolar, linear-lanceolate, with bluntly rounded to cuneate or pointed apices. In girdle view, broadly rectangular with widely curved apex. Cells 93–95 µm long and 35–40 µm wide. Corrugated areas covered by fine striae ranging from 40–50 in 10 µm. Striae are biseriate with fine rounded areolae, 2 in 10 µm. At present, this taxon is considered cosmopolitan.

Plate 89: Surirella robusta (a) & (b) LM; (c) & (d) HD and (e) & (f) SEM