Chapter 27, Problem 25A

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 25A

Correct answer:

The correct answer is option (B) deuterosome development

Explanation of Solution

Explanation/justification for the correct answer:

Option (B) deuterosome development. In the evolutionary tree of animal phylogeny, the invertebrate chordates, such as lancelets are deuterosomes like echinoderms, but they have additional chordate features that echinoderms do not have. So, the correct answer is option (B).

Explanation for incorrect answer:

Option (A) pharyngeal pouches. Chordates are species belonging to the phylum Chordata that at some stage during their development have four distinctive characteristics-a dorsal tubular nerve cord, pharyngeal pouches, a notochord and a postanal tail. So, this is an incorrect answer.

Option (C) protostome development. Protostomes are prehistoric invertebrates while chordates and echinoderms are members of deuterostomes. So, this is an incorrect answer.

Option (D) pseudocoelom. Echinoderms form coelom in an area together with mesoderm. So, this is an incorrect answer.