Phylum ECHINODERMATA:
Body plans, feeding & locomotion
--------------- Mon. April 7 -------------
a) discrete arms with ambulacra restricted to the oral surface and clear pentaradial symmetry (crinoids, asteroids, ophiuroids)
b) arms absent, and ambulacra extend from the oral to aboral pole; varying degrees of bilateral symmetry (echinoids, holothuroids)
a) crinoids capture suspended particles with simple, mucus-covered podia bordering the pinnules of long feather-like arms; ciliated grooves move food to the mouth
b) ophiuroids capture suspended or deposited particles with simple, mucus-covered podia or spines bordering the arms or mucus nets; a bolus of particles is moved toward the mouth by podia
c) holothuroids capture suspended or deposited particles with large, branched, mucus-covered tentacles (modified buccal podia); the entire tentacle is drawn through the mouth to ingest food
d) irregular echinoids (sand-dollars, heart urchins) live in sediment; many small podia underneath spines move particles to branching grooves in the test and then along grooves to the mouth
a) asteroids are mostly scavengers or carnivores; primitively, they swallow prey whole, but most can evert their stomach to feed
b) regular echinoids ('true' urchins) feed on algae & encrusting invertebrates with a remarkable scraping device: Aristotle's lantern
a) slender, jointed appendages (cirri in mobile crinoids)
b) coordinated tube feet (asteroids, regular echinoids, holothuroids)
c) rapid whip-like movement of arms (ophiuroids)
d) undulation of entire body (some holothuroids)
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Copyright © 1997 by A. Richard Palmer. All rights reserved.(revised April 7, 1997)