Characteristic features of phylum Echinodermata

  1. Habitat:
  • They are commonly called spiny skinned animals.
  • All are marine, generally live in sea bottom and are slowly moving animals.
  • Some animals are pelagic (free swimming in open water) and few are sessile (attached to the substratum).
  1. Body structure:
  • They are variably shaped; star shaped, spherical, cylindrical etc.
  • Head is absent and the body bears spines and
  • The adults are radially symmetrical (pentamerous radial symmetry) and the larvae are bilaterally symmetrical.
  • The body is triploblastic with outer ciliated epidermis, middle dermis and inner peritoneum.
  • Dermis has a calcareous plate and muscles are smooth.
  • Body cavity is in the form of enterocoelous coelom that is surrounded by ciliated peritoneum.
  1. Water vascular system:
  • Body is provided with water vascular system or ambulacral system.
  • The inlet canal called madreporite is present as a perforated plate.
  • Tube-feet of this system help in locomotion, respiration and food capturing.
  • Tube feet consist of ampulla, podium and sucker.
  • Digestive tract is complete but incomplete in some forms like brittle star.
  1. Circulatory system:
  • It is of open type and consists of five radiating vessels.
  • Heart is absent and instead of blood vascular system, there is presence of haemal and perihaemal system.
  • Blood doesn’t contain any respiratory pigment.
  1. Respiratory system:
  • Dermal branchiae or papulae present in star fish, peristominal gills in sea urchin and genital bursae in the brittle star help in respiration.
  • Cloacal respiratory trees are found in Holothurians in which the lower branch is called cuverian organs (protective in function).
  1. Excretory system:
  • Generally, it is absent and they are ammonotelic.
  • Excretion is by wandering amoebocytes.
  1. Nervous system:
  • Brain is absent but the nerve ring and radial nerve cords are present.
  • Autotomy and regeneration are well marked.
  1. Reproduction:
  • It takes place sexually.
  • The sexes are separate and in except few forms fertilization is external.
  • Few are viviparous and the development is indirect.
  • Larva is ciliated, bilaterally symmetrical and after metamorphosis, adult becomes radially symmetrical.
  • Bipinnaria and Brachiolaria are the larval forms in star fish, Ophioputeus in brittle star, Pleteus in sea urchin, Auricularia in sea cucumber and Doliolaria in feather star.


  • Phylum Echinodermata is divided into two sub-phyla; Pelmatozoa and Eleutherozoa.
  • Pelmatozoa has only one living class Crinoidea.
  • Eleutherozoa has four living classes; Holothroidea, Echinoidea, Asteroidea and

Class: Crinoidea

  • Mouth is usually central and anus is eccentric. Both are present on the oral surface.
  • Water vascular system and madreporite are absent.
  • Spines and pedicellariae are present.
  • They are commonly called sea lilies or feather stars.
  • Development is indirect and the larva is Doliolaria.
  • e.g. Antedon, Metacrinus

Class: Holothuroidea

  • Mouth is surrounded by a set of tentacles attached to the water vascular system.
  • Alimentary canal is long and coiled and cloaca is supplied with respiratory trees for respiration.
  • They are commonly called sea cucumbers.
  • Development is indirect with Auricularia larva.
  • Autotomy is by evisceration (removal or viscera).
  • e.g. Holothuria, Thyone

Class: Echinoidea

  • Mouth is centrally located on the oral surface while anus is on the aboral surface.
  • They have jaw suspension called Aristotle’s Lantern (i.e. chewing apparatus).
  • They are commonly called sea urchins and sand dollars.
  • Development is indirect with Echinopliteus larva.
  • e.g. Echinus, Clypeaster

Class: Asteroidea

  • They have pentamerous radial symmetry.
  • Mouth is pentagonal, centrally placed on the oral surface while anus is on the aboral surface.
  • Madreporite is on the dorsal side.
  • Endoskeleton is flexible and is made up of separate ossicles.
  • They are commonly called star fish or sea stars.
  • Development is indirect with Bipinnaria or Brachiolaria larvae.
  • e.g Solaster, Asterias (star fish)

Class: Ophiuroidea

  • The oral and aboral surfaces are distinct.
  • Ambulacral groove, anus and intestine are absent.
  • Autotomy of arms are commonly observed in brittle stars.
  • Development is indirect and the larva is Pluteus larva.
  • e.g. Ophiothrix, Ophioderma

Characteristic features of phylum Echinodermata