1. Echinoderms and Invertebrate Chordates
Chapter 31
Echinoderms and Invertebrate Chordates

2. 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

3. 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

4. “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

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

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

7. 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

8. 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

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

10. 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

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

12. 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

13. 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

14. 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

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

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

17. 6. Sea Daisies
Discovered in 1986
Radial symmetry
No arms

18. 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

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

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

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

22. 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

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