Invertebrate

An invertebrate (in contrast to a vertebrate), is an animal with no spine. Most living things are invertebrates, including arthropods, molluscs, and bacteria.

Sharks and rays are a special class under this description, since they do not have bony skeletons, and hence no spine. They do, however, have a similar structure to vertebrates. They are called notochords.

The phyla contained in Invertebrata are:

• Protozoa - Mostly simple, single-celled organisms
• Porifera - Sponges
• Coelentera - Hydra, jellyfish, anenomes and corals
• Echinoderma - Starfish, sea urchins and sea cucumbers
• Annelida - Worms
• Brachiopoda - Bivalves, such as mussels and clams
• Polyzoa - Single celled criiters that usually form colonies
• Mullusca - Whelks, ammonites, cuttlefish, squids, snails, etc.
• Arthropoda - Crustaceans, insects, arachnids, trilobites, etc.