CHAPTER SEVEN:
AQUATIC MACRO INVERTEBRATES
Ibrahim, Baba Usman
Invertebrate organisms are animals without backbones. They existed in two forms micro invertebrates and macro invertebrates. The micro invertebrates are minute in nature and are visible only with the aid of microscope while the macro invertebrates are multicellular and can be visible with the naked eye. The micro invertebrates include the protozoa, coelenterate, Rotifera etc. The macro invertebrates comprise of larger animals, Arthropoda, Mollusca with shells, flat worms platyhelminthes, Annelida etc.
The focus shall be on the aquatic macro invertebrates. The fauna content of fresh waters differs greatly from that of the sea and oceans. Only a comparatively small number of fishes, crustaceans and mollusks can migrate from the sea into fresh waters or vice versa. This mixing of fresh water and marine fauna is observed at the mouths of the large Siberian rivers and inland seas of low salt content in the U.S.S.R. e.g. the sea of Azov and the Baltic Sea. In general, the animal population of rivers and lakes differs considerably from that of the seas. Major group of animals (e.g. the entire phylum Echinodermata, the subphylum Urochodata, the class Cephalopod mollusks etc.) are not represented by even one species in fresh waters. Isolated coelenterate and polychaetae forms are found in fresh waters. The fauna of sponges, bryozoans, gilled snails and many other groups is much poorer in fresh waters than in the sea. Some groups of aquatic animals are more diverse and more abundant in fresh water than in the sea e.g. Cladocerans (water fleas), phyllopods, rotifers, water oligochaetae, archinids and tardigrades. Aquatic insects one of the most important animal groups inhabiting fresh waters are almost entirely absent from the marine fauna. Some fresh water animals are entirely adapted to life in water. All stages of their life cycle occur in an aquatic environment e.g. protozoans, worms, crustaceans, mollusks. Almost all insects live in water during some developmental stages only in the adult stage they leave the water. Spiders are associated in part with aquatic environment.
The aquatic macro invertebrates which is the main focus includes:-
PLATYHELMINTHES
They are triploblastic, acoelomate, unsegmented, flattened animals (flatworms) under leaves or stones, on muds at the bottom of lakes or streams in tropical high lands. They are divided into three classes, two of them Trematodes and Cestoda are parasitic, while the Turbellaria are free living. The larvae of the parasitic forms (flakes) live in the body of certain snails (e.g. Lymnea). The free living kinds are brownish or greenish. They are carnivorous or feed on debris. The planarians are also flatworm inhabiting standing and flowing water. Fig. 1.
NEMATODA
They are round worms. Non segmented. Mostly microscopic or too small to be seen easily. Between lum and l0 um long, with strong flexing movements e.g. Rhadbolaimus aquaticus. The fresh water nematodes are found in flowing and standing waters of all types. Most of them are predators and non-parasitic and protected by their very thick cuticle fig. 2.
ANNELIDA
They are segmented worm, divided into three classes, Polychaetae, Oligochaetae and Hirudinea, those with a sucker at each end, but have no bristles e.g. Hirudinea / sleeches. This group of annelids inhabits fresh waters predominantly and only a few species are marine. Many leeches are parasites of fish, turtles and water fowl. Only a few species e.g. the medicinal leech (Hirudo medicinealis), Haementeria costata and the middle Asian limnatis can pierce the skin and feed on the blood of man. Fig.3. The second groups of annelida have no suckers but have bristles present in their body e.g. the earthworms and the fresh water worms. They are large in polluted water in Africa e.g. Yoruba worm (Limnodrilus sp.), and the smaller worms found among plant roots in marsh area e.g. Potworms (Enchytraeus sp.), and in the mud at the bottom of lake or pond etc. e.g. Tubifex, Nair, and Dero Fig. 3.
Plate: Platyhelminthes (Flat worms) and Nematoda (Round worm)
Source: Phyllis (1965)
AQUATIC MACRO INVERTEBRATES
Plate: Annelida (Hirudinea)
Source: Phyllis (1965)
ARTHROPODA
The arthropoda has jointed limbs in adults and external hard skeleton. They comprise of the following groups:-
The insecta with three pairs of legs in adults and sometimes none in the larvae. A large number of species belonging to class insecta are associated with fresh waters .e.g. water bettles and with very few exceptions insecta not marine. Water bettles and water bugs pass their entire life span in water. Most aquatic insects live in the air during their winged stage, only the eggs, larvae and in some group the pupae are associated with an aquatic environment.
The insecta has three subdivision as follows:-
a. Those that fly over or settle on water, they are further divided into two i.e. those with one pair of wings including mosquitoes e.g. culex, Aedes settle with body parallel to the surface of water, and Anopheles mosquito settle with body at an angle head down. Black fly e.g. Simulium. And those with two pairs of wings including Caddis flies e.g. chimera, Stone flies e.g. Neoperla, Mayflies e.g. Cloeon , Dragon flies e.g. Pantala.
b. Those that run on water surface including pond skaters e.g. Gerrir, water crickets e.g. Velia, Whirling beetles e.g. Gyrinus, water measurers e.g. Hydrometra.
c. Those that live in or under water are subdivided into two (i) those with biting mouth parts e.g. water beetles and (ii) those with piecing mouth parts with forewings leathery comprising of water bugs e.g. Belostoma , lethocerus, water boatman e.g. Notonecta, water scorpion e.g. lacotrephes and water stick insects e.g.. Ranatra. Fig 4.
d. The Arachinida has four pairs of legs e.g. spiders and mites. The spiders (Araneina) are large 1cm or more and are represented in ponds laters and creeks of small rivulets by a single aquatic species, the water spider (Argyroneta aquatica). The water mites (Acarina) are small 1mm - 3mm.
The crustacean has more than 4 pairs of legs comprising of two subdivisions fresh water crabs e.g. Deckenia, potamonautes, trichodactylus - they are broad, flattened carapace, and abdomen folded beneath. And the fresh water shrimps e.g. Palaemon, caridina, they are longer with cylindrical carapace large abdomen. Fig. 5.
Plate : Insecta ( Phyllum Arthropoda)
Source : Phyllis (1965)
Plate : Insecta ( Phyllum Arthropoda)
Source : Phyllis (1965)
INSECT LARVAE
Insect larvae form a considerable part of aquatic macro invertebraes, they have obvious mouth parts but no wings. The following were classified based on the position they occupied in the aquatic habitat.
a. Those hanging from surface of water or surface film include Mosquito larvae (Culex sp. hang at an angle 1cm), anopheles sp Larva hang at an angle 1cm and Rat-tailed Maggot Eristalis sp found in stagnant water in some tropical area at 5cm.
b. Those that are motionless in mid-water e.g. lake flies phantom larvae Chaoborus sp 1cm.
c. Those on the bottom or amongst vegetation e.g. Blood worm Chironomus sp 11/2cm and midge lavae e.g. Tanytarsus 1/2cm.
d. Those Larvae with three pairs of legs form another classification, with two subdivisions, (i) Those living freely with one (1) tail filament include Alder Flies e.g. Sialis rare in the tropic (ii) Those with two (2) tail filaments comprise stone fly larvae e.g. Neoperla, some beetle larvae e.g. Eretes, gyrinus and some caddis larvae usually with two hooks, (iii) those with three (3) tail filaments include dragon fly larvae e.g. Pantala, Aushna, Damsel fly larvae e.g. Ischnura and may fly larvae e.g. Cloeon, Baetis Fig. 6.
AQUATIC MACRO INVERTEBRATES
Plate: Insect larvae
Source: Phyllis (1965)
Plate: Insect larvae
Source: Phyllis (1965)
Plate: Insecta (Phyllum Arthropoda)
Source: Phyllis (1965)
MOLLUSCA
Mollusca are divided into two major groups, Gastropoda and Lamellibranchia. The Gastropoda possess 1 valve to shell, coiled or cap shaped and subdivided into two:
i. Those with operculum and gill comprise of Nerites (neritidae) e.g. Neritina, Apple snail (Ampullaridae) e.g. Pila, Lanistes, Pomaceae, Asolane, and Viviparous snails (Viviparidae) e.g. Bellamaya viyipara.
ii. Those that lack operculum, have lung, but no gill. Comprise of freshwater limpets (Ancylidae) e.g. Bunopia, Ancylus, pond snails Lymnaeidae e.g. Lymnaea, Bulinus and Ramshorn snails (Planorbidae) e.g. Austrlorbis, Indoplanorbis, and Biompholarria Fig. 7.
The diversity of aquatic macro invertebrates is very great, and their classification based on their adaptation to the environment of the habitat, the position they occupied in the habitat and the structure they possess or modification of these structures in relation to functions such as defence i.e. bitting and piercing or modification for nutritional purpose. It is also important to note that some of the aquatic macro-invertebrates are harmful or parasitic e.g. Leech, mosquitoes which are vectors of malaria parasites, while some serve as food for other aquatic inhabitats like fish e.g. earthworms of Oligochaetae group.
Plate: Mollusca (divided into two major groups, Gastropoda and Lamellibranchia)
Source: Phyllis (1965)
References
Carol, M. L. and Timothy, R.P. (1993). Biological Oceanography: An Introduction. Pergamon Press NewYork 186 – 197pp.
Dejoux et. al. (1981). Illustrated Catalogue of Aquatic Insects in the Ivory Coast. Hydrobiologist ORSTORM TOME II Paris. 34 – 42pp.
Phyllis, M.M. et. al., (1965). Hulton’s Biological Field Studies. Tropical Fresh Water Ecology. Hutton Educational Publications Limited 13 – 49pp.
Zhadin, V.I. and Gerd, S.V. (1961). Fauna and Flora of the Rivers, Lakes and Reservoirs of the U.S.S.R. Keters Press Binding Weiner Bindery Ltd. Jerusalem 49 – 99pp.