ECHINARACHNIUS (SAND DOLLAR)​

CLASSIFICATION OF ECHINARACHNIUS OR SAND DOLLAR​

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 :- IRREGULARIA (Periproct displaced towards mouth in innerradius.)

ORDER :- CLYPEASTEROIDA (Body disk-shaped, ambulacra petaloid and anus displaced laterally.)

GENUS :- Echinarachnius (The sand dollar)

GEOGRAPHICAL DISTRIBUTION

  • It is found along West coast on North America, Pacific coast and U.S.A.

HABIT AND HABITAT

  • Echinarachinus is commonly found about 800 fathoms deep, lying on sand or partly buried.

ECHINARACHNIUS OR SAND DOLLAR​

GENERAL CHARACTERSTICS OF ECHINARACHNIUS OR SAND DOLLAR​

  • Commonly called as sand dollar.
  • Body is circular, disk-like and dorsoventrally flattened and differentiated into oral and aboral surface. 
  • Oral surface is composed of inter-locking ambulacral and interambulacral ossicles beset with tiny spines.
  • Five petaloid ambulacra representing opening for tube feet in double row in the form of a petal. One present on aboral surface. 
  • Petaloid also contain paired openings for flattened respiratory tube feet.
  • Entire test has small spines. Madreporite plate, ocular plate and genital plate with genital opening are found on aboral surface. 
  • Anus is aboral.
  •  Development includes echinopluteus larva.
ECHINARACHNIUS OR SAND DOLLAR​

IDENTIFICATION

  • The animal contains five petaloid and all above features hence it is Echinarachnius.

ECHINARACHNIUS OR SAND DOLLAR​
ECHINARACHNIUS OR SAND DOLLAR​
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