Pearly Brooch Clam
Neotrigonia lamarckii (Gray, 1838)
Family Trigoniidae (Pearly Brooch Clams)
Neotrigonia is a very unusual bivalve. The family is really small, with only one genus (Neotrigonia) and ten species worldwide alive today, all in deep water off Australia. The family was much more diverse in the Cretaceous Period (100 million years ago), with five subfamilies and more than 15 genera, but most went extinct during the K-T mass extinction. As a result, trigoniids are often called “living fossils.” Their closest relatives are the freshwater unionoids or pearl mussels, although the two groups superficially look nothing alike. Inside, Neotrigonia is beautifully nacreous, lined with mother of pearl. Other notable characteristics are their beaded-radial sculpture, disctinctive and complex shell hinge teeth, and the unusual muscular foot used for rapid burrowing, which you can see in this photograph. This specimen was collected alive in the Coral Sea off North Stradbroke Island, Queensland, Australia, during BivAToL’s expedition to Moreton Bay in October 2008. It was dredged from about 45 meters (150 feet). One member of this family, Pterotrigonia thoracica (Morton, 1834), is the official state fossil of Tennessee.
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.