INVERTEBRATE ANIMALS. They are those animals that lack notocorda or spine. They make up the majority of animals. In 2005, 1 were catalogued. 700 . 000 to 1. 800 . 000 animals, of which 990. 000 were invertebrates. They are invertebrates Arthropods : arachnids, insects, myryapods, crustaceans. Annelids : earthworms, leeches. Molluscs : clams, squid, octopuses, snails. Echinoderms : starfish and sea urchins. Cnidarians : jellyfish, corals, polyps. Porfers : sponges . Platelmintos : flatworms (many are parasites). Nematodes : cylindrical worms (also parasites).