Chapter 28, Problem 2STP

Summary Introduction

Introduction:

Echinoderms are marine creatures, including sea stars, sea urchins, brittle stars, sea urchins, sea lilies, sea cucumbers, and sea daisies. Echinoderms are deuterostomes since their mouth differs from elsewhere in the gastrointestinal tract. Almost 6000 living species of echinoderms have been found.

Answer to Problem 2STP

Correct answer:

The correct answer is option (B) bilateral in larval stage, radial in adult stage.

Explanation of Solution

Explanation/justification for the correct answer:

Option (B) is bilateral in larval stage, radial in adult stage. Radial symmetry and bilateral symmetry are two different types of biological symmetry found in organisms. The main difference between bilateral and radial and symmetry is that radial symmetry receives the same body half around the middle axis, while bilateral symmetry provides only two sides as right and left. All of the echinoderms have radial symmetry as adults. They have five arms radiating out of the central disk in a brittle star. Echinoderm larvae, however, have bilateral symmetry. So, the correct answer is option (B).

Explanation for incorrect answer:

Option (A) is bilateral in larval stage, bilateral in adult stage. In echinoderms, the larval stage shows bilateral symmetry and the adult stage shows radial body symmetry. So, this is an incorrect option.

Option (C) is radial in larval stage, bilateral in adult stage. All echinoderms have radial body symmetry as adults but in larval stage they show bilateral symmetry. So, this is an incorrect answer.

Option (D) is radial in larval stage, radial in adult stage. Radial symmetry generates the same body half around the central axis. The adult stage of echinoderms show the radial body symmetry but in larval stage they show bilateral symmetry. So, this is an incorrect answer.