POLYZOA. 



303 



Cyphonautes (fig. 133) forms at certain seasons of the year 

 one of the commonest captures in the surface net. It was origi- 

 nally described by Ehrenberg, but the important discovery of its 

 true nature as the larva of Membranipora (the common species C. 

 compressus is the larva of Mem. pilosa), a genus of the chilosto- 

 matous Polyzoa, was made by Schneider (No. 322). The younger 

 stages of the larva have not been worked out, but from a 

 comparison with the last described larva it is easy to make out 

 the general relationship of the parts. The larva has a triangular 

 form with an aboral apex, corresponding with the summit of the 

 dome of the Flustrella larva, and an oral base. It is enclosed in 

 a bivalve shell, the two valves of which meet along the two sides, 

 but are separate along the base. At the apex an opening is left 

 between the two valves, through which a ciliated disc (/. g) of 

 the same character and nature as that of previous larvae can be 

 protruded. 



The oral side or base is girthed by a somewhat sinuous 

 ciliated edge, which is continued round the anterior and posterior 

 extremities of the oral disc. It is no doubt equivalent to the 

 ciliated ring of other larvae. Two openings are present on the 

 oral face, both enclosed in a special lobe of the ciliated ring. 

 The larger of these leads 

 into a depression, which 

 may be called the ves- 

 tibule; and is situated 

 on the posterior side of 

 the oral surface. The 

 smaller of the two, on 

 the anterior side, leads 

 into a cavity which is 

 apparently (Hatschek) 

 equivalent to the rudi- 

 mentary bud or dorsal 

 organ of other larvae. 

 The deeper part of the 

 vestibule leads into the 

 mouth (m) and oesopha- 

 gus ; the latter is con- 

 tinued till close to the 



CYPHONAUTES (LARVA OF MEM- 

 ( After Hatschek.) 



FIG. 133 

 BRANIPORA). 



m. mouth; a. anus; f.g. ciliated disc; x. 

 problematical body (probably a bud). 



apex of the larva, there bends upon 



