Invertebrate
An invertebrate is an animal that does not have a spinal column or backbone. This contrasts with vertebrate: if an animal is not a vertebrate (fish, reptile, amphibian, bird, or mammal), it is an invertebrate. Most animals, and most species of animal, are invertebrates.
The main phyla (groups) of invertebrate animals are:
- Annelida: segmented worms
- Arthropods: (arachnids, crustaceans, insects, and others); the largest groups of invertebrates.
- Brachiopods: the lamp-shells.
- Bryozoa: sea mats or moss animals (sometimes they look like corals)
- Cnidarians: jellyfish, sea anemones, hydroids.
- Echinoderms: starfish, sea urchins, sea cucumbers
- Molluscs: (gastropods, cephalopods, bivalves and others); a large group of invertebrates.
- Nematoda: roundworms
- Porifera: sponges
- Platyhelminthes: flatworms
- Rotifers: tiny "wheel animals", which live in habitats such as pond water.
Insects and other arthropods have no bones, but they have a skeleton on the outside of their bodies, called an exoskeleton.
There are 18 more groups of invertebrates, mostly minor: see List of animal phyla.