Chapter 27, Problem 3A

Summary Introduction

Introduction: Echinoderms are deuterostomes which represent a significant transition in animal phylogeny. Echinoderms are aquatic mammals, and are the only species to have a deuterosome development and an endoskeleton in evolutionary history.

Answer to Problem 3A

Correct answer:

The correct answer is option (A) sea pen.

Explanation of Solution

Explanation/justification for the correct answer:

Option (A) is sea pen. Sea pen belongs to the Phylum Cnidaria. Some family members look like the typical quill pen while others lack the feathery texture, and can have a club-shaped or circular shape.So, the correct answer is option (A).

Explanation for incorrect answer:

Option (B) is sea star. Many sea star species have solid arms grouped around a middle disc. Sea stars can be observed in deeper water near the coast as the tide recedes, and in tide pools. They can be found in communities that stick to rocks with their tubular feet. So, this is an incorrect answer.

Option(C) is sea lily. Fossil records indicate that sea lilies and feather stars are the most primitive of echinoderms and common before the development of other echinoderms. Sea lilies have a floral body at the tip of a long stalk while feather stars' long-branched bodies radiate outward from a central field.So, this is an incorrect answer.

Option (D) is sea cucumber. Sea cucumbers are not like other echinoderms. They look like animated cucumbers that crawl across the sea floor. So, this is an incorrect answer.