Distribution Of Echinodermata In Space

The Crinoidea are represented by comparatively few forms in recent seas, and these have mostly a very local distribution. More than one hundred and fifty species of Comatula (in the wide sense) are known, ranging from 820 N. lat. to Kerguelen's Land, but most abundant in the tropics. Holopus is a West Indian form, and the species of Pentacrinus are principally West Indian also. Rhizocrimis Lofotensis occurs in the North Atlantic, and another species of this genus is found in the Gulf of Mexico. Lastly, the species of Bathycrinus and Hyocrinus are found at great depths in the Atlantic and Pacific.

The Asteroidea, Ophiuroidea, and Echinoidea are represented in almost all seas, whether in tropical or temperate zones, extending their range even into high northern and southern latitudes. They have also a wide bathymetrical range, extending from between tide-marks to almost the greatest depths which have yet been explored by the dredge. Some of the Sea-urchins (such as Toxopneustes Hindus) have the peculiar habit of hollowing out cavities for themselves in the solid rock, in which they spend their existence. The Holothuroidea enjoy a nearly world-wide distribution; but they have their metropolis in the Pacific Ocean, occurring abundantly on the coral-reefs of the Polynesian Archipelago. One species (Holothuria argus) is collected in large numbers, and is exported to China, where it is regarded as a great delicacy.