Echinoderms “spiny skinned” Ex: starfish, sea urchins, sea cucumbers, sand dollars.
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Transcript of Echinoderms “spiny skinned” Ex: starfish, sea urchins, sea cucumbers, sand dollars.
Echinoderms“spiny skinned”
Ex: starfish, sea urchins, sea cucumbers, sand dollars
Starfish body planCentral disk with radiating arms (usually 5)
Pentaradial symmetry (no head, mouth is on underside of disk)
Rigid body due to calcareous plates and spines
Endoskeleton (embedded in flesh)
LocomotionWater vascular systemWater enters via sieve plate, then drawn down a tube
to ring canal (encircles disk)
5 radial canals arise from ring canal connected to tube feet
Tube feet end in ampulla which contracts, thus forcing water into the tube feet and extending the foot. The foot then contracts and pulls the animal forward
DigestionMove slowly, prey on clams or oysters
Pulls shell apart by pulling in feet in turn until clam is exhausted and relaxes its muscles
Extends stomach into clam inside out and takes in material
Doesn’t need an intestine because all material is digested by the 5 pairs of digestive glands ( 1 pair per arm)
RespirationLarge coelom between body wall and digestive
tract are lined by cilia (these open into skin gills which diffuse oxygen in and carbon dioxide out)
Skin gills are protected by spines and pedicillaria (small pincers)
ExcretionBy ameboid cells in the coelomic fluid. Engulf
nitrogenous waste then escape through the skin gills
Nervous systemSimple because the organism is slow
Ring nerve circles the mouth and branches into 5 radial nerves
Poorly developed sense organs
Sensory cells (touch) are all over the surface
Eyespots at the tip of each arm
ReproductionOvaries or testes lie in each arm
Eggs and sperm are released into sea (broadcast method)
Has a free swimming larva (which has cilia and has bilateral symmetry, not radial like the adults)
Regeneration – one arm can turn into a new animal as long as it has most of the central disk