Understanding Echinoderms: Sea Stars, Sea Urchins, and More

2. GENERAL CHARACTERISTICS • Ex: sea stars, brittle stars, sand dollars, sea urchins, & sea cucumbers • All marine • “Spiny-Skinned Animals” • Radial Symmetry as adults – 5 parts • Regenerate = Autotomy

3. GENERAL MORPHOLOGY • A.INTERNAL SKELETON of Calcareous ossicles (plates) • Variations : Brittle / Sea Stars – many small plates that move with one another

4. Sea Urchin & Sand Dollar – skeleton plates fused into shell called “test”

5. Sea Cucumber – degenerated & buried in leathery body

6. Network of canals – run throughout body ending w/tube feet B. Water Vascular System • Used in locomotion, food capture, & respiration • Varying internal water pressure can extend or contract tube feet • Tube feet end in small suction cups

7. C. • Mouth on oral surface (bottom / ventral) • Anus on aboral surface (top / dorsal)

8. ECHINODERM TYPES

9. SEA STARS • 5 Arms / Rays 4 – 10” • Prey on bivalves (clams, mussels) & coral • Many eat w/stomach outside body; pop stomach out mouth

10. Body Plan • 2 – 4 rows of tube feet on each ray extend from ambulacral groove

11. Water Vascular System • Water enters madreporite on aboral surface into a short, straight stone canal • Stone canal connects to circular canal around the mouth = ring canal. • Enters five radial canals extending down each arm

12. Water Vascular System • Radial canals carry water to hundreds of paired tube feet. • Bulb-like sacs or ampulla on tube feet contract & create suction

13. Other Body Systems • No circulatory, excretory, or respiratory systems • No head or brain • Eyespots on the tips of each arm detect light

14. Reproduction • Separate sexes • External fertilization • Females produce 200,000,000 eggs / season; meroplankton

18. BRITTLE STARS • Most mobile; fast • Snake-like movement • Disc .4 – 1.2 “; arms 2 – 2.4 “ • Scavengers • In largest class (with basket stars) • Arms break off readily

20. BRITTLE STAR LARVA

21. SEA CUCUMBERS • Lack arms& visible spines; elongated • Flexible, leathery body • Burrowers

22. 5 rows of tube feet run length of body • 10-30 modified tube feet form tentacles around mouth • Tentacles have sticky ends to trap plankton; or eat detritus • Breathes through anus

23. Eject internal organs to scare predators (evisceration) ; regenerate in days • Symbiosis with Pearl Fish which lives in its anus. • Feed on gonads by day

26. Filter Feeders Can detach & move around Sea lilies & feather stars

27. Sea Urchins • Spines for protection, moving, trapping food • Shell = test • Divided into 10 sections • 5 Ambulacral w/tube feet • 5 Interambulacral without • Covered w/muscle & skin to help mobility

28. Tube feet – moving, capturing food • Pedicellarea – cleaning & defense • Aristotle’s Lantern – 5 teeth together like bird’s beak; to scrape algae from rocks

30. Sand Dollars • Flattened version of urchin • Live in sand along coastlines • Food falls between dense spines & carried to mouth by cilia & tube feet • Tiny, moveable spines for burrowing • Aristotle’s Lantern

32. Sea Biscuits • Not as flat as dollars • Live in sand along coastlines; burrow • Tube feet for respiration • Pedicellarea • Eat detritus in sand    • Short dense spines for movement cover test