IV. GASTEROPODA: PULMONATA 



335 



The head and usually eyes and tentacles are lacking, while the fins 

 (greatly developed parapodia) are highly characteristic, giving the name 

 'wing-footed' to these forms. They have rarely a single ctenidium. 

 The THECASOMATA have shells, Limacinid^, Hyaleid/E- The shells of 



Fig. 343. Fig. 344. 



Fig. 343. — Hyalcea complanala from above (after Gegenbaur). a, anus; br, gill; 

 c, heart; g, gonad; h, liver; m, mantle; oe, oesophagus; re, nephridium; ^', stomach; 

 //, pedal ganglion and otocyst. 



Fig. 344. — A, Clione papilionacea.* 



Cavolinid^ make the 'pterpod ooze' of the deep seas. GYMNOSOMATA; 

 shell lacking. Pneumodermon, Clioiie* Sub Order III. NUDIBRANCHIA. 

 Shell, ctenidia, and osphradia lacking; most possessing accessory gills (cerata) of 

 varying form and distribution. Doridiid^ (Fig. 345J. Tritoniid^, JEolivx 



Fig. 345. — Doris bilamellata* 



Fig. 346. — ^Solidia papulosa (from 

 Ludwig-Leunis) . 



(Dendronotus*) ; Elysiid.e, cerata lacking. In ^olida: branches of the diges- 

 tive tract enter the cerata, expand distally to small sacs filled with nettle cells 

 (p. 207) used for defense; they are derived from hydroids on which these 

 animals feed 



Order III. Pulmonata. 



In several respects the Pulmonata are intermediate between the Proso- 

 branchs and Opisthobranchs. Like the latter they are orthoneurous and her- 

 maphroditic (fig. 339). On the other hand, the respiratory organ is far forwards 



