What Are Invertebrates?

By Troy Harrington Woodard

Invertebrates are animals without backbones. They span about 97% of the animal kingdom. There are 8 invertebrate phyla (singluar, phylum): Arthropods, Sponges, Mollusks, Cnidarians, Echinoderms, Flatworms, Roundworms, and Annelids.

Arthropods

Arthropods cope with no backbone by having a hard and waxy exoskeleton, which makes then not los a lot of water to evaporation. this caused them to be the first animals to live on land and water.

Sponges

Sponges hold together without skeletons because they have tough proteins called spongin, thus their name. However they wouldn’t stand up outside of water

Mollusks

Most mollusks have hard shells that hold up soft bodies. However squids and other tentacle animals have internal or eternal skeletons.

Cnidarians

Cnidarians do not really have any solid substance to them some attach to solid things and face outward. Others float freely. Although both use tentacles to kill their prey

Echinoderms

Echinoderms survive without a spine because they have a series of plates in their skin made of calcium that hold them together.

Flatworms

Flatworms don’t really have much except a skin that holds them together. They only need to float about and some are parasitic.

Roundworms

Roundworms are round and like flat worms in most other ways

Annelids

Annelids are segmented worms. However they are more closely related to crabs and snails then roundworms or flatworms