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BIO2231: Phylum Echinodermata characteristics

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Monash University

PHYLUM ECHINODERMATA Characteristics of Phylum Echinodermata: o 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 o Living in marine habitats o Free-living taxa o Body segmented (nonmetameric) with pentaradial symmetry body rounded, cylindrical, or star-shaped, with five or more radiating areas, or ambulacra, alternating with interambulacral areas; no head o Tripoblastic body o Coelom extensive, forming perivisceral cavity and cavity of water- vascular system; coelom of enterocoelous type; coelomic fluid with amebocytes o Endoskeleton of dermal calcareous ossicles with spines or of calcareous spicules in dermis; covered by epidermis (ciliated in most); pedicellariae (in some) o Digestive system usually complete; axial or coiled; anus absent in ophiuroids o 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. o 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 o No brain; few specialized sensory organs; sensory system of tactile and chemoreceptors, podia, terminal tentacles, photoreceptors, and statocysts o Autotomy and regeneration of lost parts conspicuous; asexual reproduction by fragmentation in some o Sexes separate (except a few hermaphroditic) with large gonads, single in holothuroids but multiple in most; simple ducts, with no elaborate couplatory apparatus or secondary sexual structure
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