AP BIOLOGY

Detailed explanation-1: -Echinoderms are a phylum of marine invertebrates that include starfish, brittle stars, sea cucumbers, sea urchins, sand dollars, and crinoids. They are one of the most diverse groups of marine invertebrates and play important ecological roles from the near-shore environment to the deep seas.

Detailed explanation-2: -Echinoderms are “spiny-skinned” invertebrate animals that live only in marine environments.

Detailed explanation-3: -Echinoderms are named for the spines or bumps covering the outer surface of the bodies of many of them (Greek root word echino-meaning spiny; Latin root word-derm meaning skin). Examples of echinoderms include sea stars, sea urchins, sea cucumbers, brittle stars, and feather stars (Fig. 3.83).

Detailed explanation-4: -Found only in salt water, more than a thousand species of sea cucumbers exist around the world. These squishy invertebrates are echinoderms, making them distant relatives to starfish and urchins. Unlike starfish or sea urchins, the bodies of sea cucumbers are covered with soft, leathery skin instead of hard spines.

Detailed explanation-5: -Sea urchins and all other echinoderms are invertebrate deuterostomes and, together with the hemichordates, form a sister group to the chordates.