A New Species of Misidentified Penitella (Bivalvia: Pholadidae) from Japan and Environs

Abstract

Pholadid bivalves in the genus Penitella Valenciennes are well represented in Japanese molluscan literature and have most often been cited as either Pholadidea or Penitella kamakurensis (Yokoyama) (i.e., Jouannetia kamakurensis Yokoyama, 1922). However, the binomen Penitella kamakurensis has most commonly been applied to two different species, one being the large Penitella gabbii (Tryon, 1863), and the other of a quite distinct smaller species, here described as Penitella aikoae n. sp. Penitella aikoae n. sp. differs from all other species in the genus by its short, almost straight (not distinctly concave) anterior-dorsal margin, a rounded, not posteriorly pointed, mesoplax (umbonal accessory plate), a short, thickened, leafy periostracal fringe on the posterior margin of the shell, and an incomplete callum that only partially closes the anterior pedal gape in the adult stage.