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