PHYLUM: ECHINODERMATA = Spiny skins

PHYLUM: ECHINODERMATA = Spiny skins

1. 5 Classes → Crinoidea (sea lilies & feather stars), Asteroidea (sea stars), Ophiuroidea (brittle stars), Echinoidea (sea urchins & sand dollars) & Holothuroidea (sea cucumbers); 7 000 living species

2. Size range → < 1 cm -- > 2 m (sea cucumbers)

3. Habitats → exclusively marine, with exception of few brackish water forms All benthic (except a few pelagic sea cucumbers) → consitute up to 95% of deep-sea biomass

4. Anatomy → well-developed coelom forming a water vascular system (web of channels & reservoirs)

5. endoskeleton composed of calcareous ossicles

6. non-centralized nervous system

7. pentamerous radial symmetry (secondary acquisition)

8. larvae with bilateral symmetry (pluteus etc.)

9. WATER-VASCULAR SYSTEM (WVS)

   • Unique to echinoderms
   • Most developed in Asteroids- locomotion
   • Derived from coelom
   • Operates in locomotion as a hydraulic system
   • Canals filled with fluid & with ciliated epithelium
   • Internal canals of wvs link to outside via madreporite aborally Madreporite with furrows, pores and ciliated epithelium Pore canals lead to vertical stone canal Stone canal has calcareous deposit in walls Stone canal leads to disc/circular canal/water ring Water ring with 4 or 5 pairs of folded pouches…Tiedemann’s bodies, produce coelomic fluid
   • Ciliated radial canals extend into each arm Lateral canals on entire length of radial canal and enters coelom LC valved and ends in a bulb and tube foot Bulb = ampulla..a muscular sac Ampullae bulge into aboral side of coelom Ampulla opens into tube foot/podium Podium = short, tubular, an external projection of body wall Tip of podium forms sucker
   • Podium covered with ciliated epithelium Longitudinal muscle fibres in podium Contraction on one side bends podium Podia in 2 or 4 rows
   • WVS filled with fluid---similar to sea water Plus proteins and potassium System operates during locomotion Ampulla contracts, valves in lc close, water forced into podium which elongates Podium once in contact with surface…sucker adheres Longitudinal muscles contract to shorten podium, fluid forced back to ampulla
   • Maintenance of water pressure important for operation of ampullae and podium Podium swings forward, tube feet perform same step as animal moves forward, coordinated Suckers allow climbing vertical rocks Slow but effective movement Podium may not have suckers, pointed at tip allows burrowing in sand

10. Class 1: Crinoidea (Sea Lilies & Feather Stars)

11. Class 2: Asteroidea (Sea Stars)

12. Class 3: Ophiuroidea (Brittle Stars)

13. Class 4: Echinoidea (Sea Urchins)

14. Class 5: Holothuroidea (Sea Cucumbers)