General Ecology 19 



LOCOMOTION 



Locomotion in the family Planorbidae is accomplished by the same means 

 as in the family Lymnaeidae (see Baker, 1911, p. 32). The method most 

 usually observed is that of gliding. Tlie planorbids have been observed to 

 rise suddenly and descend abruptly, as do the lymnaeids, by varying the 

 amount of air in or on the body or shell. The members of the family are 

 usually very active, crawling about on aquarium walls quite rapidly, eat- 

 ing everything in their i)ath. In locomotion the planorbids resemble the 

 physas more than the lymnaeids. the latter usually being rather sluggish 

 in motion. Young and immature planorbids are usually very active, much 

 more so than fully mature individuals. 



FOOD 



Like the lymnaeids the food of the planorbids is largely vegetal. Little is 

 known, however, concerning the food sujiply of this family. They have 

 been observed eating pond-lily leaves (principally Castalia), Potamogeton, 

 both the large floating leaf species and the submerged leaf species, and 

 algae of various kinds. Both old and young snails will eat avidly of the 

 algal scum which collects on the glass sides of an aquarium. The radula can 

 be plainly seen, the animal using it from behind forward as described by 

 Dr. v. Sterki many years ago. 



Stomachs and crops that have been opened and examined have usually 

 contained a quantity of fine sand (especially in the crop) which probably 

 helps in grinding the food before it enters the intestine. Ostracods (six in 

 one specimen of Helisoma subcrenatum from Pass Lake, Fidalgo Island, 

 Washington) , distomids, vegetable fibers, and a quantity of flocculent un- 

 digested animal matter have been noted in the stomach. Specimens of 

 Helisoma duryi seminole from Florida had the stomach and gizzard filled 

 with small grains of sand and nothing else. Some planorbids are scavengers, 

 though not to the extent observed among the lymnaeids. No evidences have 

 come under observation indicating that the group is carnivorous (see 

 Baker, 1911, p. 42 for notes on the food of lymnaeas). 



FOOD FOR OTHER ANIMALS 



Together with other fresh-water mollusks, the family Planorbidae fur- 

 nishes food for a large number of other forms of animal life. Chief among 

 the animal groups feeding on mollusks are certain species of fish (see 

 F. C. Baker, 1916). Fresh-water snails, including planorbids, have been 

 found in the stomachs of the following food and game fish: 



Whitefi.sh (Coregotms clupeaformis (Mitchill) ) 

 Small Mouth Buffalo (Ictiobus bubahis (Raf.) ) 

 Common Sucker {Catostomus commersonii (Lacepede) ) 

 Yellow Bullhead (Ameiurus imtalus (LeSueur) ) 

 Common Bullhead (Ameiurus nebidosus (LeSueur) ) 

 Fre.sh\vater Drum (Aplodinotus grunniens Raf.) 

 Pumpkinseed (Lepomis gibbosus (Linn.) ) 

 Bluegill (Lepomis macrochirus Raf.) 



