ISO MANUAL OF ZOOLOGY. 



anchor-shaped, calcareous spicules, placed upon little papillae 

 of the integument. Respiration is effected in the abdominal 

 cavity; into which the water is admitted by five openings 

 between the tentacles. The Synapta live in the mud, but they 

 form for themselves a kind of case or tube composed of 

 particles of sand. They obtain their food by swallowing sand 

 or mud, from which they extract any nutrient particles which 

 may be contained therein. 



The order Holothuroidea may be divided into the following 

 two families : 



Family I. Holothuridce. 



Body free, cylindrical, with a coriaceous integument containing 

 scattered calcareous particles. An ambulacral system always, and a 

 respiratory tree usually, present. 



Family II. Synaptida. 



Body free, covered with a coriaceous, sometimes soft, integument, 

 containing minute, anchor-shaped spicules, by means of which the 

 animal moves. The ambulacral system rudimentary, not giving rise 

 to tube-feet, and not connected with locomotion. A respiratory tree 

 sometimes present, sometimes absent. 



CHAPTER XXIII. 



DISTRIBUTION OF ECHINODERMATA IN SPACE 

 AND TIME. 



DISTRIBUTION OF ECHINODERMATA IN SPACE. The Crinoidea 

 are represented by very few forms in recent seas, and these 

 have a very local distribution. The Comatula are the com- 

 monest, and species have been found in most seas. The 

 Pentacrinus Caput-Meduscz is exclusively confined, as far as is 

 known, to the Caribbean Sea. Rhizocrinus Lofotensis has been 

 dredged on the coast of Norway, and in the North Atlantic, 

 and a form believed to be the same has been found in the 

 Gulf of Mexico. In the North Atlantic also, has been found 

 another Apiocrinoid, which has been described under the name 

 of Bathycrinus grarilis. 



The Asteroidea, Ophiuroidea, and Echinoidea are represented 

 in almost all seas, whether in tropical or temperate zones, 

 some occurring very far north. The Holothuroidea have their 

 metropolis in the Pacific Ocean, occurring abundantly on the 

 coral-reefs of the Polynesian Archipelago. One species is col- 

 lected in large numbers, and is exported to China, where it is 

 regarded as a great delicacy. 



