CLASSIFICATION OF ECHINUS OR SEA URCHIN​

KINGDOM :- ANIMALIA (Multicellular eukaryotic organisms)

PHYLUM :- ECHINODERMATA (Coelomate, pentaradiate and spiny skinned animals with vascular system.)

SUB-PHYLUM :- ELEUTHEROZOA (Non-pedicellate and free-living.)

CLASS :-ECHINOIDEA (Body oval or spherical and composed of test)

SUB-CLASS :- REGULARIA OR ENDOCYCLIA (Periproct and peristome, aboral and oral respectively.)

ORDER :- ECHINOIDA (Simultaneously possessing both an un-sculpted test and a feeding lantern with large plates fused across the top of each pyramid)

GENUS :- Echinus (Sea urchin)

GEOGRAPHICAL DISTRIBUTION

  • It is widely distributed in the Atlantic, the Mediterranean and Pacific waters.

HABIT AND HABITAT

  • Echinus is a benthic animal occurring from inter-tidal zone to a depth of 5000 meters.

GENERAL CHARACTERSTICS OF ECHINUS OR SEA URCHIN​

  • Commonly called as sea urchin. 
  • Body is spherical and brownish and is differentiated into flat, oral and domed aboral surfaces along vertical oral aboral axis. 
  • Body is enclosed in a rigid globular test or corona which is composed of calcareous plates which regularly interlock to form test. 
  • Entire surface, except peristome and periproct, is covered by movable articulated spines to the test. 
  • Pedicellariae and sphaeridia, offensive and defensive organs are found between movable articulated spines. The oral surface contains mouth, from where jaw apparatus or Aristotle’s lantern or masticatory apparatus protrudes internally. The mouth is surrounded by a lip or peristome. The inside of peristome contains calcareous ossicles and buccal tube and on outer edge of peristome are ten branching gills.
  • Test is distinguished into ambulacral and inter-ambulacral zones. Water vascular system is well developed. Ambulacral groove closed. 
  • Test bears numerous spines and rows of tube feet in ambulacral areas.
  • Dried test contains ocular plates, anus, genital plate, madreporite plate and double row of podia. 
  • Madreporite and gonophore are present near anus and aboral in position. 
  • Tube feet end in suckers and form five double meridional rows.

SPECIAL FEATURES

  • The mouth on lower surface is surrounded by a lip or peristome. In side of peristome contains calcareous ossicles and buccal tube and on outer edge of peristome are ten branching gills. The most interesting part is Aristotle’s lantern. It is a masticatory apparatus which protrudes internally. Sea urchin’s eggs have been extensively used for experimental work in embryology.

IDENTIFICATION

  • The animal contains rounded test and all above features, hence it is Echinus.

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