3.14 



MOLLUSCA 



lion. RTIACITTOLOSSA; siphoiidslonialc. |irc(Ialory, >tri;u-im- [}fi'rrx. Fiir- 

 fiurj.'' i'r,>Stiifiii!.v-) sccrcic a Mili>lancc lurninj; |>ur|>le by c\pi>sui-c lo air, Ty- 

 rian purple was produccil In' Miinx Ininculiis. Uri>sdlpiiix i!iii'r<iis''' drills inlo 

 oysters. lii'ceixiD.v . whelks, \ Oi urLU.K, and (.li.nm.i: helonj; here. TOXl- 

 c;LOSS-\; CoMD.i:, wiih ivsopliageal poison L;land. T.ENIOGLOSSA; 

 X.\TiciD.v. -V<:'i77/,;,* iMiuUia:-' Li rroKiMP.v; periwinkles. Cypr.-kui.-v, 

 cowries; Cvpru\i nwiittd used as money in .M'riea. .Vmi'I'i i.\rii>.v:; amphibious, 

 part of branehial caNilv aeling as lung, part eonlaining elenidium, T.m.udin- 

 ID.E, fresh wa'er. 



HI'.TKRlM'OD.V. In details of gills, genitalia, heart, and nervous system 

 these are true IV'Cliiiibranehs, but from an e.\elusi\el\' pelagic lile ha\e accpiired 

 peculiar modihcalions. Like most pelagic animals lhe\- are transparent The 

 head is eloni^ate. Most characterislic is the di\ision of the foot into pro- and 



Fig. :;42. — Carinaria medilcnaiica (afler Cicgcnhaur'), shell renio-i'cd. .1, mctn- 

 poiiiuni; (7, anus; ar, aorta; /■>, \iseeral sac; />/', Itranchia-, the hearl al>o\"e; <//, \as 

 tleferens; c. nroLith; cc, c\c \\ilh tentacle; cc, (.vsophai;us; /», jtroiUHliuni; />.\-, ])t.'nis; 

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



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

 The propodium is vertically flattened anti ser\es as a swimming organ. The 

 Heteropioda are predaceous and cxlremelv \oracioiis. Atl.\ntid.k anil Cakin- 

 AUiiD.E, with shells; rTia^tOTKAe-HlciD.E, without. 



Order 11. Opisthobranchia. 



The Opisthobranchia ha\e not \aried from ihc primitive svmmetrv lo such 

 an extent as have I'rosobranchs and Pulmonates. 'I"hc ;inus is in or near the 

 median line, although it ma\' be far forwards. 'I'he nervous svslem is orlho- 

 neurous, the twist being straightened (except in .VctaHmida'). 'Idle hearl also 

 retains its priniili\ e position, receiving blood from liehind and forcing it forwards 

 to the body through the ;u)rla (fig. 337"). In rare cases a ^righO elenidium, a 

 poorly developed mantle, ;\nd a thin shell occur. I'sually these h;i\e been lost 

 and the place ol (he elenidium is laken bv ;iccessorv gills of various forms or a 

 dermal respiralion occurs. The lar\a' ha\e well-develo|ied mantle and shell. 

 Many of the Opislhobranchs afford fine examples, in form and loloralion, of 

 protective resemblance. .\ll are hermaphroditic ;ind marine. 



Sub Order 1. TKCTIRRANCinA. Mantle and nsuallv shell and eleni- 

 dium present. Bulla* riiiliiir* Aj^lysia. Snb Order 11. I'TlsKOrODA 

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



