Revision of the genus Parabornia (Bivalvia: Galeommatoidea: Galeommatidae) from the Western Atlantic, with description of a new species from Brazil

Parabornia palliopapillata n. sp. (Galeommatidae) is described from small bivalves found attached to the abdomen of the stomatopod crustacean Lysiosquilla scabricauda (Lamarck) (Lysiosquillidae) from the Rio de Janeiro and São Paulo coasts, Brazil. The shell is thin, flat, white, and smooth. The hinge possesses a pair of small symmetrical cardinal teeth in each valve. The mantle border has 4 marginal folds, the third being entirely papillated, with only the umbonal region lacking papillae. The foot has a small byssus, a ventral furrow and an anterior flower-like organ. The style sac of the stomach is separated from the intestine. The incubation of ova occurs in both demibranchs. A complementary redescription of P. squillina Boss, 1965, the single species of the genus up to this time and associated with the same host, is provided, based on paratypes from Panama. The two species differ mainly in details of the mantle border, gill, digestive tract, anterior musculature and shape of the flower-like organ. A discussion of the family assignment of the genus is also provided.