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 Chordates
Invertebrate 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.