R E M J^ R IC H 



i\iidif»riiiichiate, or iVaked-CRillcil, Molliisks. 



BY R. E. C 



/r 



In the true Gasteropodo^s (Greek — 

 gasfer, belly, podex, feet), or belly-footed 

 luollusks, we find two great Orders: the 

 liranchifera (from the Latin words 

 biruidiice, gills, and fero, to bear), or 

 Gillbearers; and the Pulinonifera (from 

 the Latin pulmo, lung, and/ero, to bear), 

 or Lungbearers — the latter respiring by 

 })ulmonary sacs. 



Besides this striking difference in 

 structure, the branchiferous Gastero- 

 pods pass through a distinct larval stage, 

 and come from the egg in a very differ- 

 ent form from that which they present 

 when they are mature, or in the adult 

 stage. 



The pulmoniferous mollusks undergo 

 no such metamorphosis. 



The Branchifera are divided into two 

 sub -orders according to the position of 

 the gills, and the sub -orders are again 

 divided into groups. 



One of these sub -orders is called the 

 Opiailiobfanclilata (from the Greek word 

 apidUoi<, behind, and brandikv, gills), 

 and it is this group to which I refer here- 

 in. The second great group of the sub- 

 order OpldhobrancUiata is the Nudi- 

 branddala, or naked-gilled crawlers. 

 The animals, as would be inferred from 

 the i^^ame of the group, are destitute of 



. STEARNS. 



^3 



shells, except during the embryonic pe- 

 riod, when these delicately constructed 

 creatures are furnished with a small 

 glassy spiral shell, and can swim in the 

 water freely ; but as they advance in 

 age the form of the bod}' is modified, 

 an.d the shell falls oft' In the matter 

 of sexual development, they are her- 

 maphrodite ; they are also carnivorous 

 in their food, which consists principally 

 of zoophytes. 



The Nudibranchiates are divided into 

 three principal families : the yEuIidce, 

 which have the gills along each side of 

 the back; the Tritonida;, which resem- 

 ble ^^(jluhe somewhat in form and posi- 

 tion of the gills, but present other 

 structural differences, which warrant 

 their separation as a family ; and the 

 BorUhv, generally of broader form and 

 larger size than the two preceding fam- 

 ilies, as well as of tougher substance, 

 which have the gills placed in a circle 

 on the back and generally in the hinder 

 part of the body. The gills or bran- 

 chial plumes are of very elegant forms, 

 and frequently present the appearance 

 of Fern -leaves, or similar graceful and 

 feathery shapes; the foot (or belly) is 

 much smaller than the mantle (or back, 

 as seen from above). 



