The Channeled Duck Clam, Raeta plicatella (Lamarck, 1818), is a bivalve commonly found in Southwest Florida. Its closer relative locally is the less common Smooth Duck Clam, Anatina anatina (Spengler, 1802), with which it could be confused (this latter species was featured in his column on October 10, 2014.) Both species have very thin, fragile shells. The Channeled Duck Clam, however, shows a sculpture of broad concentric ribs and a more rounded outline. The Channeled Duck Clam, as other species of the family Mactridae, has its two siphons (one sucks water in for filter-feeding, the other expels the used water) fused to form a single, elephant trunk-like structure. In addition, species in the family Mactridae have their hinge with an internal ligament, in contrast to most bivalves, which display an external ligament. (The ligament is the proteinaceous, usually brown, part of the hinge that keeps the shell slightly open when the strong adductor muscles are relaxed; when threatened or uncomfortable, the bivalve shuts its shell by contracting its muscles.)
The Channeled Duck Clam, Raeta plicatella, in internal, top, and external views. Photos by José H. Leal.