Chapter 31

Echinoderms and Invertebrate Chordates

Section 1: Echinoderms

Section 2: Invertebrates Chordates

Section 1

Echinoderms

Objectives:•Compare the developmental pattern found in protostomes with that found in deuterostomes.•Describe the major characteristics of echinoderms.•Summarize how the sea star's water vascular system functions.

Section 1

Echinoderms

Animal Development•Protostomes During embryonic development, a protostome’s mouth develops from the blastopore.•Deuterostomes In a deuterostome, the anus forms from the blastopore and the mouth forms later from a different opening. •Echinoderms and Chordates Because echinoderms and chordates are both deuterostomes, scientists believe that both groups were derived from a common ancestor.

Section 1

Echinoderms

Modern Echinoderms•Body Systems Echinoderms lack a head or brain. Their nervous system consists of a central ring of nerves with branches extending into each of the five parts of its body plan. In many echinoderm species, respiration and waste removal are performed by skin gills.•Shared Traits Echinoderms share four characteristics: an endoskeleton composed of ossicles; five-part radial symmetry; a water-vascular system; and coelomic circulation and respiration.

Section 1

Echinoderms

Echinoderm Diversity•Sea Stars Sea stars pry open prey using their tube feet.•Brittle Stars Brittle stars are relatives of sea stars.•Sea Lillies and Feather Stars Sea lillies and feather stars are the most ancient and primitive living echinoderms.•Sea Urchins and Sand Dollars Sea urchins and sea dollars lack distinct arms but have the basic five-part body plan.

Section 1

Echinoderms

Echinoderm Diversity continued•Sea Cucumbers Sea cucumbers are soft-bodied, sluglike animals without arms.•Sea Daisies Sea daisies are strange disk-shaped little animals that are a new class of echinoderms.

Section 2

Invertebrate Chordates

Objectives:•Describe the characteristics of chordates.•Define the term invertebrate chordate.•Compare tunicates and lancelets.

Section 2

Invertebrate Chordates

The Chordate Skeleton•Chordates Phylum Chordata includes invertebrate and vertebrate chordates.•Other Chordate Characteristics At some point in their lives, all chordates have a notochord, a dorsal nerve chord, pharyngeal slits, and a postanal tail.

Section 2

Invertebrate ChordatesInvertebrate Chordates•Invertebrate Chordates Invertebrate chordates do not have a backbone (vertebral column). Two invertebrate subphyla are Urochordata (tunicates) and Cephalochordata (lancelets).•Tunicates Tunicate larvae have a nerve cord, notochord, pharyngeal slits, and a postanal tail. As adults, they lose all of these characteristics except the pharyngeal slits.•Lancelets Lancelets retain their notochord, dorsal nerve cord, pharyngeal slits, and postanal tail into adulthood.