1) They are found in sea and are most common and widely distributed.
2) They are found in all seas from the intertidal zone to the great depth.
3) They are usually radial symmetry always pentamerous
4) They have triploblastic body,without clearly differentiated head and segmentation.
5) They have round to cylindrical or star shaped with simple arms radiating from central disc or branched
feathery arms arise from a central body .
6) They are medium sized to considerable size but non are microscopic.
7) They have body covered by five symmetrical spaced radiating grooves called ambulacra with five alternative inter -radii or inter ambulacra.
8) They have endoskeleton consisting of closely fitted plates which form a shell called theca or test or made
up of separate ossicle.
9) They have spacious coelom which is lined by peritoneum and is occupied by digestive and reproductive
system.The peritoneum is developed from embryonic archenteron.
10)They have water vascular or ambulacral system consisting of tubes filled by watery fluid.
11) They have coiled tube alimentary canal extending from mouth that is located on the oral surface to the anus on the aboral or oral surface.
12) They have circulatory system or haemal system or blood lacunar system in their body.
13) They breath through papulae,peristomial gills, genital bursae and cloacal respiratory trees.
14) They have primitive nervous system which consists of networks gathered into the radial ganglionated nerve cords.
15) They do not have well developed sense organs.
16) Most of them have sex organs in two separate body except few of them.They have simple gonads with or without simple ducts.
17) They usually reproduce sexual but few reproduce asexually by regeneration.
18) They have fertilization taking place externally but few of them also are viviparous .
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