Phylum Echinodermata

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Phylum Echinodermata

• marine only
• radial symmetry oral/aboral surfaces
• calcareous endoskeleton made of ossicles
• lack excretory circulatory system
• non-metameric
• regenerative

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Natural History

• benthic predators scavengers
• two part stomach
• cardiac stomach may be everted
• pyloric stomach contains the gastric caecae
  increased surface area
• reproduction
• mostly dioecious
• external fertilization
• swimming larvae (bilaterally symmetrical,
  ciliated)

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Class Crinoidea

• sea lilies feather stars
• most primitive extant group
• tropics mainly
• long, feathery arms around the mouth suspension
  feeders

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Class Echinoidea

• sea urchins, sand dollars, sea biscuits
• spherical test without arms
• pentamerous plates with long movable spines
• algae or deposits

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Class Holothuroidea

• sea cucumbers
• reduced endoskeleton leathery body
• secondarily bilateral
• tube feet modified as tentacles
• evisceration-

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Class Stelleroidea

• brittle stars starfish
• most diverse group
• autotomy- arms detach readily
• distinct central disk

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