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A top shell usually confined to a narrow tidal zone on 

 European Atlantic shores is Osilinus Uneatus. It lives 

 on fairly bare rock covered by water about half the 

 time. (England. Ralph Buchsbaum) 



OPISTHOBRANCHS 



Marine opisthobranch snails usually go through a 

 shell-producing stage and then stop, or even obliter- 

 ate the shell completely. Presumably these animals 

 have an extremely disagreeable flavor, for almost 

 nothing will eat them, with or without armor. Per- 

 haps this is why the sea hare Tethys californica, 

 which feeds on seaweeds, so often reaches a length 

 of 15 inches and a weight of fifteen pounds. It has 

 only a vestige of shell, completely hidden by large, 

 fleshy folds of the mantle. The similarity to a rabbit is 



suggested by a pair of upright ear-shaped organs 

 (rhinophores) on the back of the head; they are be- 

 lieved to be organs of taste. If a sea hare is dis- 

 turbed, it gives off a great flood of purple fluid, often 

 concealing its own yellowish to greenish color 

 (Plate 60). 



Among the most bizarre of mollusks are the sea 

 slugs or nudibranchs, which lack a shell altogether 

 (Plates 61-69). They are fancifully colored and 

 wear a highly decorative tuft of plumes (ceratia) 

 upon the back as elaborations of the mantle. These 

 have a respiratory role; gills are lacking. Nudibranchs 

 creep over seaweeds and hydroids, browsing upon 

 coelenterates and bryozoans. Aeolids (Aeolis and 

 related genera) even digest away all of a coelenterate 

 except its stinging cells, and transfer these weapons 

 intact and undischarged into the surface tissues of the 

 plume filaments and sensory projections. In this way 

 the aeolid uses the hydroid's weapons long after the 

 coelenterate itself has been absorbed as food. 



In warmer seas far from land, the deep violet- 

 blue nudibranch Glaitciis eiicharis creeps along on 

 the underside of the surface film, scavenging for 

 minute plants and animals. Branched extensions of 

 its body make a strikingly symmetrical pattern as 

 seen from air, but its color provides Glaiiciis with 

 excellent camouflage over deep water. 



Pond snails often travel in the same way along the 

 water film, and waves of movement in the exposed 

 foot can be watched as crosswise bands shifting 

 from front to back. At intervals a pond snail presses 

 its mantle against the surface film and opens a dark 

 pore through which it can exhale and inhale a lung- 

 ful of air. Land snails and slugs breathe with a sim- 

 ilar lung cavity in the mantle. While active they dis- 

 play the pore every few minutes, closing it between 

 one breath and the next. 



The common snails include larger Lyimmea with 

 right-handed shells (coiling clockwise as viewed from 

 the open end), smaller Physa with a left-handed 

 shell, and the wheel snails {Pkmorbis) with a flat 

 spiral. Many of these creatures are a mixed blessing. 

 They serve as important food for fish in which man is 

 interested, but also as the intermediate hosts for 

 dangerous parasites among the flatworms and flukes. 

 Some fresh-water snails live as much as 1 20 feet be- 

 low the surface of lakes, where the oxygen supply is 

 very limited. Others thrive in marshes around Lake 

 Titicaca in the mountains of southern Peru, 12,550 

 feet above sea level. 



Terrestrial snails and slugs are mostly scaven- 

 gers, feeding on decaying vegetation. A few are 

 strictly carnivorous, some burrowing in pursuit of 

 earthworms, others hunting for insects, other snails 

 and slugs, and carrion. Slugs have been known to 

 enter beehives, apparently raiding for honey. 



Black turban snails, Tegtila funehralis, form great 

 clusters in crevices and on rocky surfaces from Alaska 

 to Lower California. Their shells are afterward ap- 

 propriated by small hermit crabs. (Oregon. Ralph 

 Buchsbaum ) 



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