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Characteristics of Phylum Echinodermata


1.- Unique water-vascular system of coelomic origin extends from body surface as series of tentacle-like projections

     (podia, or tube feet) protracted by increase of fluid pressure within them; opening to exterior (madreporite or

     hydropore) usually present.


2.- Living in marine habitats.


3.- Free-living taxa.


4.- Body unsegmented (nonmetameric) with pentaradial symmetry; body rounded, cylindrical, or star-shaped, with five       or more radiating areas, or ambulacra, alternating with interambulacral areas; no head.


5.- Triploblastic body.


6.- Coelom extensive, forming perivisceral cavity and cavity of water-vascular system; coelom of enterocoelous type;

      coelomic fluid with amebocytes.


7.- Endoskeleton of dermal calcareous ossicles with spines or of calcareous spicules in dermis; covered by epidermis

     (ciliated in most); pedicellariae (in some).


8.- Digestive system usually complete; axial or coiled; anus absent in ophiuroids.


9.- Skeletal elements connected by ligaments of mutable collagenous tissue under neural control, ligaments can be              “locked” into rigid posture or relaxed to allow free movement at will; locomotion by tube feet, which project from            ambulacral areas, by movement of spines, or by movement of arms, which project from central disc of body.


10.- Nervous system with circumoral ring and radial nerves; usually two or three systems of networks located at                      different levels in the body, varying in degree of development according to group.


11.- No brain; few specialized sensory organs; sensory system of tactile and chemoreceptors, podia, terminal tentacles,

      photoreceptors, and statocysts.


12.- Autotomy and regeneration of lost parts conspicuous; asexual reproduction by fragmentation in some.


13.- Sexes separate (except a few hermaphroditic) with large gonads, single in holothuroids but multiple in most; simple

      ducts, with no elaborate copulatory apparatus or secondary sexual structures; fertilization usually external; eggs

      brooded in some; development through free-swimming, bilateral, larval stages (some with direct development);

      metamorphosis to radial adult or subadult form; radial cleavage and regulative development.


14.- Excretory organs absent.


15.- Respiration by papulae, tube feet, respiratory tree (holothuroids), and bursae (ophiuroids).


16.- Blood-vascular system (hemal system) much reduced, playing little if any role in circulation, and surrounded by

       extensions of coelom (perihemal sinuses); main circulation of body fluids (coelomic fluids) by peritoneal cilia.




Integrated principles of zoology / Cleveland P. Hickman, Jr. ... [et al.]. – 14th ed. p. cm.

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