Echinoderms Ch. 28.4

 Phylum ECHINODERMATA  Spiny Skin  First Phlya with an INTERNAL skeleton  ENDOSKELETON: formed from hardened plates of Calcium Carbonate  Found only in MARINE environments

What is an Echinoderm?  Adults have NO anterior or posterior ends  No CEPHALIZATION  Bodies are still 2 sided (oral surface [where the mouth is]; aboral surface [opposite side])

 Spiny skin, internal skeleton, water vascular system, suction-cuplike tube feet  Most have 5 part RADIAL symmetry

 Radial symmetry is similar to spokes of a wheel  More closely related to humans than other vertebrates  Larva is bilateral  Deuterostomes (blastopore develops into an anus)

Form and Function in Echinoderms  Internal tubes: WATER VASCULAR SYSTEM (carries out body functions such as respiration, circulation, and movement)  Sievelike structure called MADREPORITE  Tube feet attached to radial canal  Muscles help with movement

Feeding  Can feed by scraping, capture, filtering, predation

Respiration and Circulation  Thin walled tissue of feet will provide a surface for respiration (some species have ‘skin gills’)  Circulation takes place in the water vascular system

Excretion  Solid wastes released as feces through anus  Nitrogen cellular waste are excreted as ammonia (passed into the water via diffusion)

Response  Don’t have a highly developed nervous system (they don’t even have a ‘head!’)  Nerve ring around the mouth with radial nerves  Scattered sensory cells that detect light, gravity, and dangerous chemicals

Movement  Use tube feet and a thin layer of muscle fibers attached to the ENDOSKELETON

Reproduction  External fertilization  Separate sexes  Sperm in testes, eggs in ovaries

Groups of Echinoderms  7,000 species  SEA URCHINS and SAND DOLLARS: large, solid plates; detrivores; burrow or wedge for protection  BRITTLE STARS: found on coral reefs; flexible arms that move for defense; can shed their arms; filter feeders or detrivores  SEA CUCUMBERS: warty/pickle looking; detritus and suck up food from the sea floor  SEA STARS: carnivorous; self repair when damaged  SEA LILIES and FEATHER STARS: filter feeders; live near coral reefs

Ecology of Echinoderms  A change in number of echinoderms can change the ecology  Sea urchins help with algae  Sea stars help control the number of clams and corals  Threat is CROWN of THORNS.