The Collaborative International Dictionary of English v.0.48:
Physa \Phy"sa\, prop. n. [NL., fr. Gr. fy^sa a bellows.] (Zool.) A genus of fresh-water Pulmonifera, having reversed spiral shells. See Pond snail, under Pond. [1913 Webster]WordNet (r) 3.0 (2006):
physa n 1: any member of the genus Physa