Friday, September 16, 2011

Characteristics of class Asteroidea


1)     They have flat, pentagonal or star shaped  body.
2)     Oral and aboral surfaces are distinct, the oral surface is directed downwards and the aboral surface upwards.
3)     They have  five to fifty long or short rays or arms radiating symmetrically from central disc.
4)     Mouth is centrally placed at the oral surface surrounded by a membranous peristome.
5)     Anus is small and inconspicuous located more or less eccentrically on the aboral surface .
6)     Ambulacra form prominent grooves provided with podia or the feet.
7)     Ambulacra are restricted to oral surface extending from the peristome to the tips of the arms.
8)     Endoskeleton is flexible made of separate ossicles.
9)     Pedicellariae are small, movable spine like always present
   10) They reproduce by papulae.
11) They have separate sex organs with radially arranged gonads.
12) They are commonly called starfish or sea stars.
13)They form brachiolaria larva or bipinnaria.

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