404 



APLACOPHORA 



H. Cryptoidea. — With double sutural laminae; Cryi^toconchus, 

 Amicula, Cryptocliiton. 



r 



Fig, 266. — Neovienia 

 carinata Tullb. : «, 

 anus ; gr, ventral 

 groove ; m, mouth. 



ant — ^ 



Fig. 265. — Chit07iellus fasciatus Quoy ; ant, anterior end. 



I. Chitonelloidea. — Posterior valve funnel shaped ; laminae 



thrown forward ; CMtonellus, Chone/plao:. 

 Sub-order II. Aplacophora. — Animal vermiform, foot absent, 

 or a mere groove, cuticle more or less covered 

 with spicules. 



According to Marion, one of the principal 

 authorities on the group, the Aplacophora 

 are perhaps Amphineura whose development 

 has been arrested at an early stage, their 

 worm -like exterior beint^ _ 



due to adaptation to sur- 

 roundings. They have 

 hitherto been found chiefly in the N. Atlantic 

 and Mediterranean, generally at considerable 

 depths, and often associated with certain 

 polyps in a way which suggests a kind of 

 commensalism. 



Fam. 1. Neomeniidae. — Foot a narrow 

 groove, intestinal tube without differentiated 

 liver, kidneys with common exterior orifice, 

 sexes united, ctenidia present or absent. 

 Genera; Neomenia (Fig. 266), Paramenia, 

 Proneomenia, Ismenia, Leindomenia, Don- 

 dersia. 



Fam 2. Chaetodermatidae. — ■ Body cylindrical, no ventral 

 groove, liver a single sac, kidneys with separate orifices into the 

 branchial cloaca, two bipectinate ctenidia. Single genus, Chaeto- 

 derma (Fig. 267). 



Fig. 267. ^Chaetodenna 

 iiitidulum Lov. : a, 

 anus ; m, mouth. 

 x3. 



Order II. Prosobranchiata. 



Visceral loop twisted into a figure of 8 (streptoneurous), right 



