Echinoderms and Invertebrate Chordates Chapter 31 Echinoderms and Invertebrate Chordates

I. Echinoderms A. Animal Development Animal embryos go through a gastrula stage Each gastrula has an opening to the outside called the blastopore The blastopore develops into the mouth or anus of an animal

1. Protostomes “Protos” – Greek for first; “stoma” – Greek for mouth Animals with mouths that develop from or near the blastopore first Occurs in all acoelomate animals Occurs in some coelomate animals such as annelids, mollusks, and arthropods

“Deuteros” – Greek for second 2. Deuterostomes “Deuteros” – Greek for second Animals whose anus develops from or near the blastopore first Evolved more than 650 million years ago First animals to develop an endoskeleton http://www.youtube.com/watch?v=UgT5rUQ9EmQ

B. Echinoderm Characteristics 1. Endoskeleton Calcium-rich endoskeleton composed of individual plates called ossicles Plates fuse together in adults Provides sites for muscle attachment

2. Five-part Radial Symmetry Bilaterally symmetrical as larvae The larvae’s body plan becomes radially symmetrical during their development into adults

Five arms that radiate from a central point Nervous system consists of a central ring of nerves with branches extending into each of its arms Each arm thus acts independently

Most species can regenerate a new arm if a portion of an arm is lost In some species, a complete animal can regenerate from an arm connected to a portion of the central disk

3. Water-Vascular System Water filled system of interconnected canals Tube feet extend outward through openings in ossicles - Used for feeding and gas exchange

4. Coelomic Circulation and Respiration The body cavity functions as a simple circulatory and respiration system Skin gills line the spines of an echinoderm and increase surface area through which respiratory gases can be exchanged

C. Echinoderm Diversity 1. Sea Stars Carnivores Prey on bivalve mollusks and consume coral reefs

2. Brittle Stars Slender branched arms that they move in pairs to row along the ocean floor Arms break easily Most are filter feeders Live primarily on the ocean bottom

3. Sea Lilies and Feather Stars Mouth is found on their upper surface rather than lower Sessile; attached to the ocean floor by a stalk

4. Sea Urchins and Sand Dollars Lack distinct arms Some species of sea urchins contain a venom that causes a severe burning sensation Other species have a toxin that paralyzes their prey

Sea urchins are found on rocky ocean bottoms Sand dollars live in sandy area along the sea coast

5. Sea Cucumbers Soft-bodies, sluglike animals without arms Some species are hermaphrodites Tube feet are modified into tentacles situated around its mouth

6. Sea Daisies Discovered in 1986 Radial symmetry No arms

II. Invertebrate Chordates A. The Chordate Skeleton The chordate embryo develops a stiff rod called a notochord along its back Muscles attach to the notochord

B. Other Chordate Characteristics 1. Dorsal Nerve Cord Nerves attach to a dorsal nerve cord and travel to different parts of the body

2. Pharyngeal Slits Develop in the wall of the pharynx 3. Postanal tail A tail that extends beyond the anus

C. Invertebrate Chordate Diversity 1. Tunicates (Urochordata) Larvae contain a nerve cord, notochord, and postanal tail - Lost in transformation into adulthood

Adult tunicates retain their pharyngeal slits Most are sessile, filter-feeding marine animals Hermaphrodites Water moves in an incurrent siphon, passes through its pharyngeal slits and leaves the body through the excurrent siphon As water passes over the pharyngeal slits, food is filtered from it and passes into the stomach

2. Lancelets Found worldwide in shallow ocean water Feed on microscopic protists that they filter out of the water Have separate sexes