Biology | Answers to Review Questions

Author Dr. George B. Johnson, Washington University
Author Dr. Peter H. Raven, Missouri Botanical Gardens & Washington University
Contributor Dr. Susan Singer, Carleton College
Contributor Dr. Jonathan Losos, Washington University

Answers to Review Questions

Chapter 47 (p. 944)

1. Protostome animals exhibit spiral determinate cleavage, with the blastopore becoming the mouth. Deuterostomes exhibit radial indeterminate cleavage, with the blastopore becoming the anus. The major coelomate protostome phyla include the annelids, mollusks, and arthropods.

2. Echinoderms and chordates are deuterostomes. Protostomes have spiral cleavage and determinate development. Deuterostomes have parallel cell division at right angles to the polar axis. In protostomes, the coelom arises as an enlarging space within the mesoderm. In deuterostomes, the coelom is formed from an evagination of the archenterons.

3. The symmetry is radial and there is a five-part body plan in adult echinoderms.

4. Calcium-rich plates called ossicles make up the internal skeleton, which is covered by epidermis beset with numerous spines.

5. Echinoderms respire via skin gills, which are fingerlike projections of epidermis that occur near spines. The digestive system is complete with mouth, gut, and anus.

6. The ability to regenerate lost body parts means that they can asexually reproduce from parts, and sea cucumbers in particular can eject intestinal parts as a defensive mechanism. Reproduction is usually sexual, with the sexes separate and externally indistinguishable; there is external fertilization although some species brood eggs in cavities or underneath bodies. The larvae are bilaterally symmetrical.

7. Sea cucumbers have soft bodies with leathery skin and lie on their sides so that the radial symmetry is less evident. Their tube feet form tentacles that surround the mouth. To eat, the tube feet exude mucus that captures small organisms, then the tentacles are brought to the mouth and the food organisms are wiped off within the esophagus. Their skeleton is widely separated microscopic plates. The respiratory tree has internal branches from the cloaca that function in gas exchange as water is pulled in and out. Reproductively, some are hermaphroditic.