Meeting Abstract

28.4  Jan. 5  Redescription of the freshwater bivalve Guianadesma sinuosum and implications for the historical biogeography of northern South America ARONOWSKY, A.*; ANDERSON, L.C.; HELLBERG, M.E.; Louisiana State University; Louisiana State University; Louisiana State University audrey@geol.lsu.edu

The tropical bivalve Guianadesma sinuosum Morrison, 1943 is restricted to freshwater, an uncommon habitat for either of the two clades (Corbulidae or Lyonsiidae) to which it has been assigned. In our previous morphology-based phylogenetic analyses, including both corbulid and lyonsiid species, we found G. sinuosum to be nested within the Corbulidae. Specimens attributed to G. sinuosum have been collected throughout northern South America, including the central Amazon River in Brazil; the Courantyne, Suriname, and Marowijne Rivers in Suriname; and the Demarara, Cuyuni, and Essequibo Rivers in Guyana. The discontinuity of these localities, in separate drainages, presents an interesting biogeographic problem. Further complicating the issue, specimens attributed to a nearly identical species, Anticorbula fluviatilis (Adams, 1860), have been collected from the Trombetas River, an Amazon tributary in Brazil and the Maranon River in Peru. In order to begin untangling this problem, we recollected G. sinuosum from Morrison�s type locality at Kartabo Point in the Cuyuni River of Guyana. Here, we present a redescription of G. sinuosum based on our new material and museum specimens. We will discuss new phylogenetic analyses and the potential of G. sinuosum and closely related fossils from northern South America for reconstructing the biogeographic history of this region.