--------------- Wed. April 2 -------------

• 1) The Echinodermata is an ancient marine phylum of uncertain origin

  a) perhaps the most bizarre of living animal phyla

  b) five main living classes: Crinoidea (feather stars, sea lilies), Asteroidea (starfish), Ophiuroidea (brittle stars), Echinoidea (sea urchins, sand dollars), Holothuroidea (sea cucumbers)

• 2) Pentaradial symmetry was linked to a sessile lifestyle (primitively)

  a) 'oral' & 'aboral' are more useful terms than 'anterior' & 'posterior'

  b) the oral surface is oriented up in attached forms and down in most mobile forms

• 3) Unique calcareous, dermal ossicles give the phylum its name

  a) originate intracellularly (endoskeleton) & form as a single crystal

  b) they take a remarkable variety of shapes and sizes

  c) they may: form a flexible strutwork (asteroids), form an interlocking chain of elements (ophiuroid & crinoid arms), fuse into a rigid test (echinoids), be small and isolated (holothuroids)

  d) may form the jaws of pedicellaria (some asteroids & echinoids)

  --------------- Fri. April 4 -------------

• 4) The unique water vascular system is a coelom lined with cilia

  a) the primary original function was feeding; locomotion arose later

  b) connects to the outside via a porous plate (madreporite)

  c) Polian vesicles of the ring canal help maintain internal pressure

  d) radial canals (5) extend down ambulacral grooves and may be open (crinoids, asteroids) or enclosed (other classes)

  e) lateral canals lead to tube feet that may or may not bear suckers

  f) tube feet are extended via hydrostatic pressure (via ampullae in many groups) and retracted or bent via longitudinal muscles

• 5) The early larva is bilaterally symmetrical and primitively exhibits a tri-partite coelom (axocoel, hydrocoel, somatocoel)

  a) the water-vascular system arises from the fused axo-hydrocoel

  b) the perivisceral coelom arises from the somatocoel

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