Invertebrate Overview

Invertebrates do not have backbones and make up 95% of the animals living on earth (us vertebrates are actually way way way in the minority).

We have covered molluscs, crustaceans, and echinoderms in larger units, but there are lots of other invertebrate phyla including three types of worms, sponges, and cnidarians.

Cnidarians include coral, jellies, and sea anemones and will be covered in Unit 10. They have radial symmetry and stinging tentacles surrounding their mouth.

Sponges in phyla Porifera have asymmetry because of their irregular shapes. Water flows in through many small pores and out large centralized openings called osculum. This is how sponges get their food and how they get rid of waste. Sponges have two types of structural support - spicules that are spiny or pointy and made of calcium carbonate and springy spongin. Sponges we use around the house used to be made of sponges harvested from the ocean that were pounded to remove the spicules. Now, plastic sponges are commonly used.

There are three types of worms - Flatworms (Platyhelminthes), R0undworms (Nematodes), and Segmented Worms (Annelids).

Flatworms (Platy-hel- minthes) are flat and ribbon like, have bilateral symmetry and include things like tapeworms, planarians, flukes, and brightly colored marine flatworms. Marine flatworms have similar adaptations to nudibranchs (molluscs), but are flat and have no tufts. They are simple animals and are often parasites.

Roundworms (Nematodes) are ubiquitous and found commonly worldwide in every biome... but they are poorly understood because they are very very small. Less than 5cm. They have radial symmetry and often are parasites. Roundworms have scary looking mouths with teeth for attaching - often used in scary movies.

Segmented Worms (Annelids) include earth-worms, leeches, bristle-worms, and christmas tree worms. They are more advanced than the other worms with segments and body organs. They have radial symmetry and tunnel through their food.

For those of you studying invertebrates, you can use these matching cards to help!