The simplest invertebrates, in fact the simplest animals, are sponges. Sponges feed by siphoning water into their body and filtering out food particles. Most invertebrates change form as they grow, going through a process known as metamorphosis. The caterpillar to butterfly is an obvious example. Some species of invertebrates form large colonies. Marine invertebrate colonies include corals, hydrozoans, Portuguese man-of-war, and sea squirts.
This quiz looks at invertebrates of the sea. If you'd like a closer look, just click on the photo to enlarge it.