7th Grade Science Student ebook

UNIT 5 STRUCTURE AND FUNCTION IN LIVING THINGS

Figure 15.17: Echinoderms include

starfish (top), sea urchins (middle), and

sea cucumbers (bottom).

Echinoderms and a summary of the invertebrate phyla

What are

echinoderms?

The Phylum Echinodermata (meaning “spiny skin”) includes

starfish, sea urchins, and sea cucumbers (Figure 15.17).

Echinoderms have radial symmetry, a body cavity, an

internal skeleton, and spiny skin. They also have an unusual

feature called a water vascular system. The water vascular system

is a network of fluid-filled canals connected to hundreds of tiny,

tube-like feet. The water vascular system helps them move and

capture food. Echinoderms do not have a head or a brain but they

do have specialized nerve cells that provide senses of touch, taste,

and smell. Some species have eyespots that can only detect light

and dark. All echinoderms live in marine environments. They

reproduce sexually and most have separate male and female

individuals.

Summary: the

evolution of

animal phyla

The diagram below shows evolutionary relationships among the

invertebrate phyla and vertebrates.