ZOOLOGICAL SOCIETY BULLETIN 



like an elephant's trunk, tells its owner the na- 

 ture of the object it is approaching. 



Small aquarium fishes do not molest it. and 

 next to the minnows, eels and shrimps in activ- 

 ity, the mud snail, without which no salt water 

 balanced aquarium can be complete, serves as a 

 useful and interesting pet. 



Fresh Water Snails. — There are numerous 

 species of American fresh-water snails, and 

 most of them are preyed upon, either in the 

 young or adult stage, by fishes. One of the few 

 that attains a length greater than one inch, is 

 said to avenge all the others by attacking and 

 devouring little fishes. 



The two species most commonly used in our 

 balanced aquaria come from other shores: the 

 Red Ramshorn of Europe and the large brown 

 Japanese Snail. 



The commonest of American fresh water 

 snails are the Pond Snail (Lymnaea), its near 

 relative Physa, the little fresh water limpet, 

 Ancylus, the coiled shells called ramshorns, and 

 the Potomac snail. 



The horn-colored fresh-water limpet, or river 

 limpet (Ancylus) , is a very small, sluggish and 

 almost flat snail. It is a lima: breather and has 

 been observed to spend an entire winter out of 

 water. It is hardly above a quarter of an inch 

 long, and desirable only in an aquarium for ani- 

 mals smaller than fishes, since the latter will 

 prey upon it. 



Physa is one of the species credited with re- 

 sisting dessication. It is a spiral snail with no 

 operculum and a thin shell easily crushed in a 

 fish's jaws; and most species of the pond snail 

 answer the same description, being thin-shelled 

 and doorless like Physa, slightly longer and 

 more pointed. One species of the pond snail. 

 however, found in northern New England (es- 

 pecially in Vermont) and called the Niagara 

 snail (Lymnaea stagnalis), grows to be two 

 inches in length and is large enough to be kept 

 with goldfishes. But it has the reputation of 

 capturing little fishes such as sticklebacks, also 

 small salamanders; and it will attack the plants 

 if not provided with special food, such as 

 lettuce. 



The common pond snail is the most interest- 

 ing of fresh-water snails, a pulmonate — that is 

 to say. an air breather, having a lung and no 

 gills. Crawling upside down, at the surface, on 

 its broad, flat foot, it imbibes air so audibly that 

 even small specimens can be heard sucking it in. 

 and feeds on floating vegetable and animal sub- 

 stances. Drawing small edible objects to its 

 foot, which is provided with threads of fine 



cilia, whose action attracts like a magnet, it curls 

 the foot so as to hold the food substances thus 

 captured, and carries the repast below to be de- 

 voured under water. It can drop to the bottom 

 or rise to the top in an instant, and all feats of 



ERESH- WATER LIMPET 



aquatic motion are familiar to it except that it 

 cannot swim through the water like a fish. 



Its most interesting performance is the man- 

 ner in which it ascends from the bottom on a 

 string of mucus extruded before it as it rises, 



Left: POND SNAIL: Bight: PHYSA 

 Physa is a near relative of the Pond Snail. Wlien held in the 

 same position, one shell opens to right and the other to the left. 



later descending upon the same string. These 

 mucus strings are invisible unless they remain 

 long enough to gather a covering of silt, but 

 their presence is easily detected by passing a 

 stick over or under the suspended animal. 



RED RAMSHORN SNAIL AND YOUNG 



The young — much enlarged— shown marked difference in shape 



of shell and size of eye and syphon. 



The pond snail is omnivorous, feeding largely 

 on vegetable substances, but refusing nothing 

 that is edible. A defunct comrade is soon 

 cleaned out of its shell, and no scraps left by 

 the fishes will escape the snail's attention. It is 



MUD SNAIL. EGG CASE AND YOUNG 

 Egg case and young much enlarged 



