Insects, snails, crabs, lobsters and worms are all examples of invertebrate animals. Spiders and clams are other examples. Invertebrates are animals that do not have a backbone.
Invertebrates are found in most habitats and over 95 percent of animals on earth are invertebrates. Invertebrate animals lack a vertebral column and are cold-blooded. They are a diverse and extensive group of animals, with over 1.3 million identified as of 2009.
Invertebrates are categorized into nine phyla: Porifera, Cnidaria, Platyhelminthes, Nematoda, Rotifera, Mollusca, Annelida, Arthropoda and Echinodermata.
Phylum Porifera includes sponges. Sponges are sessile filter-feeders that can reproduce both sexually asexually. There are over 5,000 species of sponges and the majority of them live in saltwater.
Jellyfish, corals and sea anemones are animals in the phylum Cnidaria. The animals in this phylum all live in the water and possess stinging cells called nematocysts.
Three of the invertebrate phyla involve worms. Phylum Platyhelminthes includes flatworms, tapeworms and other parasites. The phylum Nematoda includes roundworms such as ascarids, hookworms and pinworms. Phylum Annelida contains the segmented worms such as earthworms, ragworms and leeches.
Microscopic pseudocoelomate animals called rotifers are in phylum Rotifera. They are usually found in moist environments and freshwater.
Snails, slugs and cuttlefish are part of phylum Mollusca. These animals are known for using a radula, a toothed ribbon made of chitin, for feeding.
Phylum Arthropoda is composed of insects. All arthropods have a segmented body and an exoskeleton.
Starfish and sea urchins make up phylum Echinodermata, a phylum known for containing animals with radial symmetry.