Phylum: Echinodermata, its classification and characteristics

  • exclusively marine.
  • multicellular, system grade of body organization.
  • triploblastic, coelomate and radially symmetrical.
  • free living, free swimming or sedentary.
  • star shaped, oval shaped, globular, or discoidal with distinct oral or aboral surface.
  • literally means spiny skinned animals.
  • body surface is marked by five distinct ambulacral grooves and alternating five interambulacral area.
  • water vascular system, consists of tubes filled with watery fluid.
  • locomotion by tube feet which also helps in excretion, exchange of gases and capturing prey.
  • definite excretory organs absent.
  • respiration by papulae (skin gills) in star fish, periostomial gills in sea urchin, genital brussae in brittle star, cloacal respiratory tree in holothorians.
  • mostly unisexual.
  • development is indirect, great power of regeneration.

Echinoderm - Definition, Characteristics & Examples | Biology Dictionary

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Echinodermata is divided into two sub phylum on the basis of habit. They are:

Sub-phylum 1: Eleutherozoa

It includes all free swimming echinoderms. It is further divided into four classes. They are:

Class 1: Asteroidea

  • body is star shaped with five arms.
  • arms are not marked off from central disc.
  • open ambulacral grooves.
  • tube feet with suckers.
  • examples: Asteriae (star fish), Astropecten (sea fur)

Phylum Echinodermata |Characteristic, Classification, Importance

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Class 2: Ophiuroidea

  • body is flat and star shaped with five arms.
  • arms are separated from central disc.
  • ambulacral grooves absent or covered by ossicles.
  • tube feet without suckers.
  • examples: Ophioderma (Brittle star), Ophiothrix (spiny brittle star)

Class 3: Echinodea

  • body is oval, globular, discoidal or heart shaped without arms.
  • ambulacral grooves covered by ossicles.
  • tube feet with sucker.
  • examples:  Echinus (sea urchin), Echinocardium (Heart urchin)

Class 4:  Holothuroidea

  • body elongated without arms and spines.
  • mouth at anterior end of body surrounded by tentacles.
  • longitudinal ambulacral grooves which are concealed.
  • examples:  Cucumaria (sea cucumber), Holothuria, Mesothuria

Sub-phylum 2: Pelmatozoa

It consists of  stalked and sedentary echinoderms with one class.

Class 1: Crinoidea

  • body is attached to substratum with aboral stalk.
  • five arms bifurcated at base.
  • open ambulacral grooves covered by leaf like pinules.
  • tube feet without suckers.
  • examples:  Antedon (sea lily), Neometra (feather star)




Phylum: Echinodermata, its classification and characteristics