Phylum Echinodermata : General Characteristics

  • The term Echinodermata (Gr., echinos= spiny, derma=skin), was coined by Jacob Klein
  • Echinoderms are triploblastic, radially symmetrical (adult) often pentamerous, larva with bilateral symmetry, sessile or creeping at bottoms.
  • Echinoderms are exclusively marine deuterostomes.
  • All echinoderms are benthic ; bottom dwellers (except few pelagic sea cucumbers), mostly free living except sea lilies.
  • Spiny skinned; enterocoelic coelomate; organ system grade of organization; gregarious
  • Body is unsegmented
  • Echinoderms are uncephalized (head absent), body parts organized about an oral-aboral axis.
  • Endoskeleton (mesodermal origin) is composed of unique calcareous ossicle bearing protective spines.
  • Digestive tract is complete except Brittle star.
  • An outstanding characteristics is echinoderm is their complex coelom (enterocoel) and its ambulacral system, derivatives; the water vascular system , perivisceral coelom and haemal system.
  • Locomotion by contractile appendages of ambulacral system/ water vascular system called tube feet.
  • Tube feet consists of ampulla, podium and sucker. It also serves for respiration and food capture.
  • Presence of pinna like structure called pedicellariae that protects the skin gills.
  • Excretory system is absent.
  • Nervous system is diffused decentralized, usually consisting of nerve net, nerve ring and radial nerves, but no brain.
  • Sense organs are poorly developed and consists of tactile tentacles, pigment eye spots and statocysts.
  • Respiration by Dermal branchiae or papulae (star fish), gills (sea urchin), genital bursae(brittle star), cloacal respiratory tree (sea cucumber).
  • Circulatory system is open type : heart absent. Blood does not contain respiratory pigment.
  • Mostly dioecious, copulation absent, fertilization external.
  • Eggs are homolecithal (yolk uniformly distributed in egg)
  • Cleavage is radial and indeterminate
  • Development is indirect through free swimming larval stages.

Binod G C

I'm Binod G C (MSc), a PhD candidate in cell and molecular biology who works as a biology educator and enjoys scientific blogging. My proclivity for blogging is intended to make notes and study materials more accessible to students.

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