Varicorbula limatula (Conrad, 1846)
Family Corbulidae (Basket Clams)
The Oval Varicorbula lives epibenthically (on top of the sand) in deeper waters off the Florida Keys. These individuals, about 3,200 all together, each less than 10 mm long, were attached by byssal threads to a large spaghetti-string egg mass of some gastropod, which in turn became tangled on the “tickle chain” of a trawl at 80 feet deep off the Dry Tortugas. This fortuitous collection led to a published paper in 2001 about the anatomy of this relatively common bivalve, whose soft-parts, however, had never been described. Corbulids are represented by only about 100 living species, distributed worldwide in shallow water to the continental shelves. Most species are inequivalve, with the smaller left valve fitting neatly within the larger and more convex right valve. The heavy periostracum at the margin of the left valve seals the valves tightly when they are closed. This feature allows many species to survive in anoxic (oxygen poor) environments.
Evolution on the Half Shell...
The Assembling the Tree of Life: Bivalvia project (BivAToL) is a part of the Assembling the Tree of Life initiative, a large research effort sponsored by the National Science Foundation. Its goal is to reconstruct the evolutionary origins of all living things.
Jetsam & Flotsam
Some of the BivATOL team met in early May at the Mote Marine Laboratory’s Tropical Research Station at Summerland Key, FL for a combined collecting trip and coding workshop. Both activities are essential to our project’s goal of determining the phylogenetic relationships among the bivalve families.
After collection, many of the species’ visible and molecular characteristics must be compared and “coded,” after which the phylogenetic computer analyses will be run to produce the final “tree” from which a hypothesis of relationships can be made. Below is an example of a portion of such a phylogenetic tree. Families that are on nearby branches are more closely related to each other than those further away.