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Wednesday, September 30, 2020

Phylum Echinodermata - NEET-Biology

 Phylum Echinodermata

Fig: Sea urchin (Echinodermata)

Important characteristics:

  • Exclusively marine & benthic i.e. found at the bottom of the sea.
  • Spiny skinned free swimming, triploblastic & coelomate animals.
  • Adult echinoderms are radially symmetrical but larvae are bilaterally symmetrical.
  • Lack of head and do not show segmentation.
  • The digestive system is complete with the mouth on the ventral side & anus on the dorsal side.
  • The most characteristic feature in Echinodermata is the presence of the water vascular (or ambulacral) system. Tube feet are contractile appendages of the water vascular system; serve for locomotion, food capture, respiration & attachment of the body to the substratum. They constitute glands & filtering devices.
  • Perform sexual reproduction. Sexes are separate. Fertilization is usually external. Development is indirect with free-swimming larva.
The phylum Echinodermata is divided into two subphyla:
  • Pelmatozoa: It has a single living class Crinoidea represented by sea lilies or feather stars like Antedon, Rhizocrinus, etc.
  • Eleutherozoa: It has four living classes: Asteroidea (Asterias), Ophiothrix, Echinoidea (sea urchin), Holothuroidea (sea cucumbers).
Fig: Sea cucumber (Holothuroidea)



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