20 The Molluscan Family Planorbidae 



Many smaller fish, not of direct value as food or game fish, are yet of 

 great value as food for the larger food fish. Many of these include the 

 planorbids and other fresh-water snails in their diet. Such small fish known 

 to eat snails are: 



Fresh Water Killy {Fmululus diaphanus (LeSueur) ) 



Killifish (Fundulus dispar (Agassiz) ) 



Viviparous Top Minnow {Gamhusia affinis (Baird & 



Girard) ) 

 Manitou Darter {Pcrcino caprodes zebra (Agassiz) ) 



Five species of the planorbids have been specifically identified in the 

 stomach contents of fish. These are: 



Gyraulus parvus (Say) 

 Gyraulus deflectus obliquiis (DeKay) 

 Promenetus exacuous (Say) 

 Helisoma anceps (Menke) 

 Helisoma campanulatum (Say) 



Many species of birds, especially water birds, consume some mollusks 

 in their diet. Ducks, such as the Lesser Scaup (Nyroca affinis (Eyt.) ) and 

 others feeding in shallow water, eat fresh- water snails. The waders, such 

 as the Upland Plover (Bartramia longicauda (Bechst.) ) and the Killdeer 

 (Oxyechus vociferus (Linn.) ), feed on snails. The Red-winged Blackbird 

 {Agclaius phoeniceus (Linn.) ) has been known to feed on a planorbid 

 (probably a Gyraulus) . 



Other groups of animals which include fresh-water snails in their diet 

 are turtles, frogs, newts and salamanders, crayfish, leeches, and dragonfly 

 nymphs. It is quite probable that many other animals which frequent 

 fresh-water snail habitats feed on the smaller species or the young of 

 larger species. The stomach contents of many fish and birds have been 

 listed as simply snails or Planorbis without identification of the species 

 involved. It is obvious that the planorbids, and other snails of the fresh 

 waters, are a valuable food source for the larger animals. 



LENGTH OF LIFE 



The life span of the members of the family Planorbidae is not definitely 

 known. Specimens of Helisoma trivolvis lentum were hatched in an 

 aquarium and lived sixteen months. At this time they were about 8 mm. 

 in diameter and had four whorls. An adult lentum has five whorls and is 

 about 20 mm. in diameter. It appears possible that these specimens would 

 have attained full maturity in another year, or two and a half years from 

 time of hatching. Helisoma duryi normale has been hatched in an aquarium 

 and has lived for over a year. An adult Planorbarius corneus (the red 

 snail) has been kept alive with goldfish for two years. Mature individuals 

 of Helisoma trivolvis have remained alive for nearly two years in a well- 

 balanced aquarium. 



Just how long any of the planorbids live in their natural habitat is not 

 known, four or five years it is probable. The lymnaeids are said to live for 

 three or four years. Experiments with the larger snails of the family 

 Planorbidae, Helisoma particularly, would be of value. 



