All animals lacking a backbone are invertebrates. Invertebrates are by far the most abundant animals on Earth; there are over 2 million species that have been identified to date. It should be noted that this number make up about 98 percent of all the animals documented in the entire animal kingdom.
They can be found crawling, flying, swimming or floating.
Invertebrates can be grouped into eight (8) classes;
Aschelminthes – Most of these species are soft-bodied worms, and quite a number of them are microscopic. Almost all members are just about a millimeter long. But the species’ parasitic nematode can reach up to 13 millimeters in length. Examples are: Pheretima-earthworm and Hirudinaria-blood sucking leech).
Arthropoda – Athropods are present in every single habitat and ecosystem on our planet, and are well adapted to each and every one of these habitats. Several of them live in aquatic environments, and others reside in the terrestrial ones, some groups are even adapted for flight.
Examples of arthropods are: Some important examples of arthropods are; Honey bee, King crab, Mosquitoes, Lac insects, Locust, Centipedes, Tick and Mites.
Mollusca – The molluscs are delicate bodied invertebrates and quite a number of molluscs usually possess a foremost external shell which is hard. The phylum of the mollusk is said to be the second biggest in the world and number over a hundred thousand individual species. They have an impressive ecological adaptation, making them present in almost all habitats and are even more represented in the sea. Notable examples of mollusk are; snail, clam, oyster, squid, slug, octopus, cuttlefish, amongst others
Echinodermata – These are organisms which constitute a phylum of marine animals. They possess a superficial five-part radial symmetry, and generally equipped with peculiar tube feet. The phylum name is derived from its spiny skin. Living representatives are only found in marine environments.
Examples of echinoderms are: sand dollars, sea cucumbers, urchins, sea lily, and brittle star
Porifera – These are organisms commonly known as sponges sponges are largely fresh water and marine invertebrate animals. They are surplus on our planet and inhabit mostly the tropic waters.
Examples are: Sponges, Sycon -scypha, Spongilla -fresh water sponge and Euspongia-bath sponge.
Cnidaria– The cnidarians are an assorted of groups of invertebrates that inhabit the aquatic habita. These diverse animals are all armed with stinging cells called nematocysts. When you attempt to touch a cnidaria, their nematocysts eject barbed threads tipped with poison. The phylum cnidaria consist of over 9,000 different species.
Notable examples of cnadrians are; hydras, sea anemones, jellyfish, corals, and sea pen.
Ctenophora -They are exclusively marine animals, commonly known as sea walnuts or comb jellies. They have ciliated plates called ‘ctenes’ (combs). Their ctenes are radially arranged on the spherical body surface which the animal uses to swim.
Examples include: Pleurobranchia and Ctenophora.
Platyhelminthes – Their bodies are solid between the outer surface and the cavities of the digestive system. Many are parasitic and all lack either a circulatory or respiratory system.
Examples include: Taenia-tapeworm, Fasciola-liver fluke.