From The Collaborative International Dictionary of English v.0.48 :
Pholas \Pho"las\, n.; pl. Pholades. [NL., fr. Gr. fwla`s,
fwla`dos, a kind of mollusk.] (Zool.)
Any one of numerous species of marine bivalve mollusks of the
genus Pholas, or family Pholadid[ae]. They bore holes for
themselves in clay, peat, and soft rocks.
[1913 Webster]
From WordNet (r) 3.0 (2006) :
Pholas
n 1: type genus of the family Pholadidae: piddocks [syn:
Pholas, genus Pholas]