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Echinodermata

Echinodermata

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Echinodermata

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  1. Echinodermata

  2. I. Phylum Echinodermata (“spiny skinned” animals) A. Characteristics 1. First animals that are deuterostomates (blastopore develops into the anus) a. they are also the first to show indeterminant development and have radial cleavage 2. demonstrate secondary pentaradial symmetry ( are bilateral in the larval stage)

  3. b. as adults, echinoderms are pentamerous (five-rayed or multiple of five rays) 3.  this is the only phylum that has a water vascular system with tube feet 4.  they show no cephalization 5.  they have an inner skeleton made of plates called ossicles that are fused together to form a structure called a test 6.  most echinoderms have their mouths downward (that surface is called the oral surface) and the anus is upward (called the aboral surface) 7.  most have great powers of regeneration with a ray and part of the central disk being all that is needed to form a new individual 8. they have no circulatory system 9.  all are marine 10. most closely related to our phylum…chordata

  4. B. Class Asteroidea 1. these are the sea stars (starfish)

  5. 2. ossicles are not fused together but are extensive making movement slow and deliberate 3. most have five rays or arms…some may have as many as 40 (pentamerous)

  6. 4. move by tube feet which is controlled by the water vascular system

  7. the opening to the wvs is the madreporite, located on the aboral surface next to the anus (the whole system is a hydraulic system allowing water to enter and exit) • b.  the madreporite leads to the stone canal, then to the • c.   ring canal, then to the • d.   radial canal, then to the • e. lateral canal, then to the • f.  ampulla ( small vial-shaped vesicles), then to the • g.  tube feet ( have small suction cups) which allows the echinoderm to move ( tube feet extend out the grooves, called ambulacral grooves, on the oral surface) 5. feed by everting their stomach and having extracellular digestion a. a favorite food is bivalve mollusks

  8. 6. The crown-of-thorns sea star is slightly venomous and feeds on coral and has over 20 arms 7. sea stars have three jawed structures called pedicellaria that are part of the water vascular system which extend from the test (remove parasites; hold on to material for camouflage)

  9. C. Class Ophiuroidea (ophiur- means snake) 1. these are the brittle stars and the serpent stars

  10. 2. they have no anus 3. ossicles are not highly fused together…..move by rapid movement of the arms 4. known as brittle stars since they autotomize (auto = self; -tomy = cut) with the slightest touch 5. their arms are very flexible and move “snake-like” 6. a rather interesting brittle star with highly branched arms is called a basket star. At night it opens its arms to suspension feed, but during the day the arms “weave” around a sea fan forming a basket 7. do not have pedicellaria

  11. D. Class Echinoidea (“spiny animals” 1. includes sea urchins, sand dollars, heart urchins, and sea biscuits

  12. 2. ossicles are completely fused to form the round-like test 3. mouth is on the oral surface and the jaws of an urchin are a grinding five part structure called Aristotle’s Lantern

  13. 4. In Japan, the ripe gonads of sea urchins are eaten as a delicacy, either cooked or eaten raw in sushi 5. also have pedicellaria 6. Diadema is the black, long-spined sea urchin that is venomous 7. the larval stage of a sea urchin is called an echinopluteus larva

  14. E. Class Crinoidea (“lily animals”) 1. includes the sea lilies and feather stars

  15. 2. suspension feeders 3. mouths point upwards atop a long stem giving them a flower like appearance 4. most abundant in warm, deep tropical waters F. Class Holothuriodea 1. includes the sea cucumbers 2. they are soft bodied with greatly reduced ossicles within their skin 3. elongated animals with no rays or spines, but still pentamerous 4. respire with a respiratory system found in the anus called the respiratory tree

  16. 5. if threatened , sea cucumbers may eviscerate their guts ( eject them through the mouth) 6. one species is eaten as trepang (dried cucumber) … exploited in the Galapagos 7. pearl fish have a rather odd commensal relationship with a sea cucumber as they hide in the anus of the sea cucumber by backing into the cucumber tail-first when danger threatens

  17. G. Miscellaneous Information 1. sea stars and coelenterates were once thought to be related…..why? 2. some classification schemes have brittle stars and sea stars under one class, Stellaroidea 3. heart urchins have partial bilateral and partial radial symmetry 4. sea urchin has neither a posterior or anterior end