ZOOLOGICAL SOCIETY BULLETIN 



1591 



As previously stated, the sargassum fish is 

 entirely pelagic, and when found along the 

 shores it is there because it has followed some 

 mass of floating weed. Another fish that looks 

 to the untrained eye to be the same, but is found 

 on careful examination to be of another genus, 

 is the Marbled Angler (Antennarius scaber), 

 which lives on rocky shores and about coral 

 reefs. It can be recognized by its rough skin, 

 the skin of the sargassum fish being smooth. 



THE COMMON SNAILS. 



Their Relation to Balanced Aquaria. 



By Ida M. Mellen 



Illustrations from Sea-Shore Life and pen drawings 



by author. 



BALANCED aquaria, whether of salt or 

 fresh water, are never quite satisfactory 

 without snails ; and most snails, especially 

 very active varieties, are so attractive that no 

 one who observes them closely can help develop- 

 ing some interest in them. 



The snails are members of that group of mol- 

 luscs called gasteropods, which are character- 

 ized by an unsymmetrieal body, a well-devel- 

 oped head, and a one-piece or univalve shell 

 which is readily distinguished from the double 

 or bivalve shells of clams and oysters. 



The amount of oxygen in the water is sup- 

 posed to determine the growth of the shell. 



Snails differ in habits and structure. Some 

 ( principally the land and fresh-water species) 

 have lungs, while others (mostly the marine 

 forms) breathe with gills. There are certain 

 kinds which die very soon if they become dry. 

 and others, after spending years in a natural- 

 ist's cabinet, apparently dead, have been known 

 to resume activities when placed in water. Some 

 are separately sexed, while others are not. Most 

 snails lay eggs, but a few bring forth their 

 young alive. The hard shell of certain species, 

 provided with a horny door or operculum with 

 which the animal closes the shell's opening after 

 retreating within, serves as a protection against 

 enemies; others, with thin, doorless shells, are 

 defenseless and fall easy prey to aquatic insects, 

 beetles and fishes. 



Shells are subject to erosion from the action 

 of chemical and mechanical stimuli upon the 

 prismatic layer. 



The tongue of the snail, also called a lingual 

 ribbon, is set with even rows of minute teeth, 

 only the forward sets of which are used. As 

 these wear down, the rows behind, which are 

 continually being formed, move forward on 



their membrane, and by this process of constant 

 renewal the snail is always in possession of a 

 serviceable rasping apparatus. This is drawn 

 back and forth over a plant leaf or other edible 

 substance, scraping and comminuting it pre- 

 paratory to swallowing. 



The eyes are generally situated at the base of 

 the tentacles. 



Snails possess some powers of regeneration 

 even in the shell ; and a hole cut in the shell of 

 a common pond snail was observed to heal com- 

 pletely in six weeks. 



Salt Water Snails. — The Periwinkle (Littor- 

 ina littorea), though prettily shaped, is not 

 hardy in balanced aquaria, nor particularly to 

 be desired because of its preference for a vege- 

 table diet, which is inimical to the aquatic 

 plants. If one lives near the seashore, however, 

 he may keep periwinkles in his aquarium for a 

 few months by feeding them with sea lettuce, 

 which they will eat fresh or partly decayed. If 

 provision is made for them to crawl up out of 

 the water, they will do so, clinging to a stick 

 or stone for hours as though waiting for the tide 

 to rise. 



The Seaweed and Salt Marsh Snails (Lit- 

 torina palliata and Melampus I>ide>itntiis) are 

 also vegetarians, and fishes prey upon the latter. 



The Oyster Drill (Urosalpinx) is a hand- 

 some little shell and will survive for some time, 

 but as the presence of an oyster or clam is high- 

 ly desirable for clarification in the salt water 

 balanced aquarium and this small carpenter will 

 bore his way through either, it is obvious that 

 the helpless giants must not be placed at 

 the mercy of the Lilliputian. In truth, no other 

 molluscs, even small ones, can be maintained 

 with the oyster drill, which is a thorough can- 

 nibal. 



Other seashore snails, such as the Rock Snail 

 (Purpura lapillus), whose natural food is barn- 

 acles, have proved fairly hardy in the home 

 aquarium, but experiments to date point to the 

 conclusion that the best of all salt water snails 

 for this purpose is the mud snail. 



The Mud Snail (Nassa obsoleta) is found in 

 all parts of the world. On the Atlantic coast, 

 from Massachusetts to Florida, it is the com- 

 monest of small molluscs, darkening the rocks 

 and infesting mud flats and tide pools. 



When adult it moves only on solid surfaces, 

 though the young hang by the foot to the sur- 

 face of the water after the manner of fresh-wa- 

 ter snails. Miss Dimon, who has made special 

 studies of this species, thinks it effects locomo- 



