380 MOLL use A. 



not passing throiigli the heart. Many groups are recognized, based upon 

 the structure of the lingual ribbon. 0£ the thousands of species only a 

 few groups can be included here. KHAOIIIGLOSSA ; siphonostomate, 

 predatory. MukiciDyE (Murex, Purpura* Urofiolpinx* ) have an anal 

 gland secreting a substance first colorless, turning to purple by exposure 

 to air. The Tyrian purple was produced by Murex truncidus. TJrosalpinx 

 c»iere».s* drills into oysters. BucciNiD^, whelks, Volutid.e, and Olivid^ 

 belong here. TOXIGLOSSA ; Oonid^, with large (Esophageal poison 

 gland, some species producing severe wounds. Conus, tropical; Bele.* 

 TyENIOGLOSSA ; Naticid^, Neverita* and Lunatia*- common snail of 

 Atlantic coast, their egg-masses being the familiar sand saucers. Lit- 

 TORiNiDyE ; periwinkles. CYPR^EiDiE, cowries; Cypra'a moneta ot InAia. is, 

 used as money in Africa. Ampullarid^; amphibious, part of branchial 

 cavity acting as lung, part containing ctenidium. Paludinid^e, fresh 

 water. Cyclostomid^e, tropical terrestrial forms, the mantle cavity a 

 lung. 



HETEKOPODA. In all details of gills, genitalia, heart, and nervous 

 system these are true Pectinibranchs, but from an exclusively pelagic life 

 have acquired peculiar modifications. As in most pelagic animals the 

 body is gelatinous and transparent. The head is elongate, and the body is 

 enlarged so that usually it cannot be retracted into the shell. Most char- 

 acteristic is the division of the foot into pro- and metapodium (fig. 375), the 



Fig. 375.— Crm'iiar/a mediterranea (after Cie.fronh:iur), shell reiniiveil. A inetapodiiim ; 

 a, anus ; ar, aorta; «, visceral sac : /»■, hranchia", the heart above; df, vas def- 

 erens ; o, mouth ; Of, eye with tentacle ; a', (esophagus ; j), propodium '• ps, penis ; 

 /, //, in, cerebral, pedal, and visceral ganglia. 



lalter forming a tail-like elongation (if 1ho hudy. The propodium is vei'ti- 

 cally flattened and by its undulations serves ;is a swimming organ. The 

 llcleropoda are i)redaceous ;ind extremely voracious; they swim back 

 downwards. The ATbANTiD.r: can completely withdra.w into the shell and 

 close it with an operculum ; the Oarinariid.e (fig. ZIT)) have a shell which 

 scarcely covers the visceral complex ; the Pterhtracheid.e have no shells. 



