Chapter 27, Problem 11A

Summary Introduction

To describe:

Class ‘Concentricycloidea’.

Introduction:

Echinoderms are marine animals with spiny endoskeletons, water-vascular systems, and tube feet; they have radial symmetry as adults. Echinoderms are deuterostomes. The approximately 6000 living species of echinoderms are marine animals and include sea urchins, sea stars, and sand dollars, sea cucumbers, brittle stars, sea lilies and feather stars, and sea daisies.

Explanation of Solution

In the class Concentricycloidea, the sea daisies have been difficult to classify and study as very few have been found. They are less than 1 cm in diameter and disc-shaped with no arms. Their tube feet are located around the edge of the disc. They have five-part radial symmetry similar to other echinoderms.

Conclusion

The species in this class are very few in numbers and they do not have obvious arms.