33-i 



MOLLUSCA 



bon. RHACHIGLOSSA; siphonostomate, predatory. MuRicnxs (Murex, Pur- 

 pura* Urosalpinx*) secrete a substance turning purple by exposure to air. Ty- 

 rian purple was produced by Murex trunculus. Urosalpinx cinereus* drills into 

 oysters. BUCCINID^;, whelks, VOLUTION, and OLIVID^: belong here. TOXI- 

 GLOSSA; CONID.E, with cesophageal poison gland. T/ENIOGLOSSA; 

 NATiciDyE, Neverita* Lunatia* LITTORINID.E; periwinkles. CvpR^iDyE, 

 cowries; Cyprcra moneta used as money in Africa. AMPULLARID^E; amphibious, 

 part of branchial cavity acting as lung, part containing ctenidium. PALUDIX- 

 IDM, fresh water. 



HETEROPODA. In details of gills, genitalia, heart, and nervous system 

 these are true Pectinibranchs, but from an exclusively pelagic life have acquired 

 peculiar modifications. Like most pelagic animals they are transparent. The 

 head is elongate. Most characteristic is the division of the foot into pro- and 



FIG. 342. Carinaria mediterranea (after Gegenbaur), shell removed. A, meta- 

 podium; a, anus; ar, aorta; B, visceral sac; br, branchiae, the heart above; df, vas 

 deferens; o, mouth; oc, eye with tentacle; oe, oesophagus; />, propodium; ps, penis; 

 /, II, III, cerebral, pedal, and visceral ganglia. 



metapodium (fig. 342), the latter forming a tail-like elongation of the body. 

 The propodium is vertically flattened and serves as a swimming organ. The 

 Heteropoda are predaceous and extremely voracious. ATLANTIDVE and CARIN- 

 ARIID^:, with shells; PTEROTRACHEID^;, without. 



Order II. Opisthobranchia. 



The Opisthobranchia have not varied from the primitive symmetry to such 

 an extent as have Prosobranchs and Pulmonates. The anus is in or near the 

 median line, although it may be far forwards. The nervous system is ortho- 

 neurous, the twist being straightened (except in Actaeonida;). The heart also 

 retains its primitive position, receiving blood from behind and forcing it forwards 

 to the body through the aorta (fig. 337). In rare cases a (right) ctenidium, a 

 poorly developed mantle, and a thin shell occur. Usually these have been lost 

 and the place of the ctenidium is taken by accessor; gills of various forms or a 

 dermal respiration occurs. The larvae have well-developed mantle and shell. 

 Many of the Opisthobranchs afford fine examples, in form and coloration, of 

 protective resemblance. All are hermaphroditic and marine. 



Sub Order I. TECTIBRANCHIA. Mantle and usually shell and cteni- 

 dium present, Bulta* Philme* Aplysia. Sub Order II. PTEROPODA 

 Transparent pelagic forms which in most points agree with the Tectibranchs. 



