Deuterostome Animals

Introduction to Deuterostomes

Deuterostomes are a major group of animals known for their large body sizes and complex morphologies. They are distinguished by a unique pattern of embryonic development and exhibit high diversity in body plans, feeding methods, locomotion, and reproductive strategies.

• Definition: Deuterostomes are animals in which the anus forms before the mouth during embryonic development.

• Diversity: Includes a wide range of adult body plans, feeding methods, modes of locomotion, and reproductive strategies.

Embryological Development: Protostomes vs. Deuterostomes

Animal phyla are often classified based on embryological development, particularly the fate of the blastopore (the first opening that forms during early development).

• Protostomes ("first mouth"): The blastopore becomes the mouth; the anus forms second.

• Deuterostomes ("second mouth"): The blastopore becomes the anus; the mouth forms second.

Diagram: Embryological development diagrams typically show the blastopore's fate in both groups.

Major Phyla of Deuterostomes

Deuterostomes are divided into four main phyla:

• Echinoderms: Includes sea stars and sea urchins.

• Hemichordates: Burrowing, deposit- or suspension-feeding acorn worms.

• Xenoturbella: Two recently discovered wormlike species.

• Chordates: Includes all vertebrates (animals with backbones), such as fish, amphibians, reptiles, birds, and mammals.

Echinoderms

What Is an Echinoderm?

Echinoderms (meaning "spiny-skins") are exclusively marine animals named for the spines or spikes found in many species. There are about 7,000 described species, and they are especially abundant in shallow water environments.

• Examples: Sea stars, sea urchins, sand dollars, sea cucumbers.

Echinoderm Body Plan

Echinoderms are identified as a monophyletic group by three main synapomorphies (shared derived traits):

• Radial symmetry in adults: Most adult echinoderms exhibit pentaradial (five-sided) symmetry, although their larvae are bilaterally symmetric.

• Endoskeleton of calcium carbonate: A hard, internal skeleton that provides protection and support.

• Water vascular system: A network of fluid-filled tubes and chambers that forms a hydrostatic skeleton, used for movement and feeding. This system includes tube feet, which are elongated, fluid-filled appendages.

Additional info: The water vascular system is unique to echinoderms and is essential for locomotion, feeding, and gas exchange.

Comparison Table: Protostomes vs. Deuterostomes (Embryological Development)

Key Learning Objectives (from Chapter Outline)

• Describe the characteristics that define deuterostomes.

• Identify the major phyla of deuterostomes.

• Explain the significance of key innovations during vertebrate evolution.

• Compare primates to other vertebrates.

• Compare echinoderms and chordates to other deuterostomes.

Summary

• Deuterostomes are a diverse and complex group of animals defined by embryological development and include some of the largest and most complex animals on Earth.

• Echinoderms are a key phylum within deuterostomes, notable for their unique body plan and water vascular system.

• Understanding the differences between protostomes and deuterostomes is fundamental to studying animal evolution and diversity.