404 ZOOLOGY SECT. 



CLASS IV.-HOLOTHUROIDEA. 



Free Echinoderms with elongated, cylindrical or five-sided body, 

 having the mouth and anus at opposite extremities. The body- 

 wall is usually only supported by scattered ossicles or spicules. 

 There is no external opening to the madreporic canal (except in 

 some Elasipoda). The surface usually exhibits five ambulacral 

 areas ; but these may be absent. There is a circlet of large oral 

 tentacles. The larva is an auricularia. This class includes the 

 Sea-cucumbers and " Beche-de-mer." 



OKDER 1. ELASIPODA. 



Holothuroidea with well-marked bilateral symmetry, with tube- 

 feet on the ventral surface (which is flattened) and papillae on the 

 dorsal. Confined to the deep sea. 



ORDER 2. PEDATA. 



Holothuroidea with tube-feet either in longitudinal rows or 

 scattered irregularly over the surface. 



ORDER 3. APODA. 



Holothuroidea devoid of tube-feet and of radial ambulacral 

 vessels. 



SUB-PHYLUM II.-PELMATOZOA. 



Echinodermata which are usually fixed at the base, and usually 

 supported on a stalk composed of a row. or rows of ossicles 

 (Fig. 347) : the mouth on the free surface, near or in the centre, and 

 having extending out from it on the oral surface a radially arranged 

 system of narrow, ciliated ambulacral grooves, having the function 

 of food-grooves, which may run between the plates of the theca, 

 on the surface of the theca, or along the oral surfaces of a system 

 of radial processes or arms given off from it. The tube-feet of 

 other Echinoderms, when represented, take the form of small, 

 tubular, strongly ciliated appendages (tentacles) without suckers : 

 the anus usually on the oral surface. 



CLASS I. CRINOIDEA. 



Mostly fixed, stalked Pelmatozoa in which there is a theca 

 comprising five regularly arranged radial and five basal plates, 

 giving off five, usually branched, jointed processes or arms ; with 

 food-grooves radiating out from the mouth along the oral surfaces 

 of the arms, and extending along their branches : the central parts 

 of the ambulacral, nervous, and reproductive systems, and of the 

 ccelome, lodged in the theca, send extensions through the arms. 



This class comprises, together with many extinct forms, the 

 only living Pelmatozoa. 



