IV. SUBKINGDOM ECHINODER- 

 MATA. 



General Characteristics. — The Eohinoderms (spiny- 

 skinned) have all the parts symmetrically arranged around 

 a central axis, thus necessitating a peculiar system of 

 radiating canals and nervous ganglia. They are all ovipa- 

 rous. They respire by a water- vasculary system permeating 

 the entire body. There is also a blood vascular system, with 

 a central contractile heart. 



'Body cylindrical ; free ; mouth forward. Holothuroide^ 



»-^i iLiy-vrM-ntj .-.-* BODT SPHERICALORPLAT; FREE; MOUTH UNDERNEATH. Echinoide». 



ECHINODERMATA.- „ 



Body STAR-SHAPED ; free; mouth underneath. Asteroidea. 



.Body CUP-SHAPED ; fixed ; mouth uppermost. GrinoidefL 



CLASS I. HOLOTHURQIDEA. 



General Characteristics. — The Holothuroids (whole- 

 mouthed) have a tough skin, sprinkled with calcareous 

 granules. The mouth is surrounded with feathery tentacles, 



Mg. IM. ^t 



Pentactafi'ondSsa, Holothuroid or Sea-cucumljer. 



and the body is worm-shaped, though constructed upon the 

 radiate plan. By means of their powerful longitudinal and 

 transverse muscles, they can disgorge their own stomachs, 

 and even throw of£ their tentacles, and, after remaining inert 

 for a season, take on a new set of the rejected organs. 



