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Ch. 28.4
 Phylum ECHINODERMATA  Spiny Skin
 First Phlya with an INTERNAL skeleton
 ENDOSKELETON: formed from hardened plates of Calcium
 Found only in MARINE environments
What is an Echinoderm?
 Adults have NO anterior or posterior ends
 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
 Internal tubes: WATER VASCULAR SYSTEM (carries out
body functions such as respiration, circulation, and
 Sievelike structure called MADREPORITE
 Tube feet attached to radial canal
 Muscles help with movement
 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
 Solid wastes released as feces through anus
 Nitrogen cellular waste are excreted as ammonia
(passed into the water via diffusion)
 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
 Use tube feet and a thin layer of muscle fibers attached
 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
 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
 Sea urchins help with algae
 Sea stars help control the number of clams and corals
 Threat is CROWN of THORNS.