Chapter 27.1, Problem 7MI

Summary Introduction

To identify:

The echinoderm that moves in the described way by completing the given chart.

Introduction: Animals belonging to the phylum Echinodermata have unusual characteristics that distinguish them from animals of other phyla. These animals are found in all the oceans of the world. They move by means of hundreds of hydraulic, suction- cup- tipped appendages and have skin covered with tiny pincers.

Answer to Problem 7MI

Echinoderm	Movement
Sea urchin	Burrows into rocky areas using movable spines
Brittle star	Makes snakelike movements using tube feet and arms
Feather star	Uses cirri to grasp soft sediments on the sea floor
Sea cucumber	Crawl using tube feet and body wall muscles

Explanation of Solution

There are different classes of echinoderms; such as sea stars, brittle stars, sea urchins, sea lilies, sea cucumbers and sea daisies. All echinoderms have tube feet and endoskeletons bearing spines. Each class shows a different type of movement.

Burrowing is a characteristic of sea urchins. They burrow into rocky areas with the help of their sharp, movable spines.

Brittle stars have five arms but lack suckers on their tube feet. So they cannot use them for movement. They move by rowing themselves quickly over the bottom rocks and sediments or by snakelike movements of their arms.

A feather star extends its arms from a central point where they are attached. They capture food by extending their tube feet and arms into water where they catch suspended organic materials.

Sea cucumbers move sluggishly by means of tube feet helped by contractions in their muscular body wall.