Above is a specimen of the lucinid bivalve Fimbria sp. from the Matmor Formation (Middle Jurassic) of Makhtesh Gadol in southern Israel. I collected it in 2007 while working with Meredith Sharpe (Wooster ’08) as she pursued the fieldwork for her Independent Study project. It is a nice specimen in part because of its preservation. A closer look (below) shows very fine detail of the shell exterior.
The shell is no longer present, though. It was originally composed of the mineral aragonite, which was dissolved away, leaving an external mold that later filled in with very fine crystals of calcite. The sculpture of the shell is exquisitely reproduced; in some places even so well as to show growth lines. Many aragonitic bivalves and gastropods are preserved this way near the top of the Matmor Formation.
Lucinid bivalves are still common today in the sea. The shell shown above is a modern Fimbria fimbriata from the Solomon Islands. They are infaunal, meaning they live burrowed in the sediment. Since they were not genetically endowed with long siphons, they use the foot to create mucus-lined tubes to the surface for access to seawater. Lucinids have an endosymbiotic relationship with sulfide-oxidizing bacteria in their gill tissues. They have a hemoglobin type that transports hydrogen sulfide to autotrophic bacteria, which in turn provide the bivalves with nutrition and enable them to survive in a variety of environments, from near deep-sea hydrothermal vents to shallow seagrass meadows.
Johann Karl Megerle von Mühlfeld (1765-1842) named Fimbria in 1811. I very much wish I had a portrait to go with that magnificent name. Megerle von Mühlfeld worked at the Naturhistorisches Museum in Vienna through the eventful Napoleonic years. He is best known for his pioneering work with insects, but he also curated the mollusk collections, which led to his description of the new Fimbria.
References:
Anderson, L.C. 2014. Relationships of internal shell features to chemosymbiosis, life position, and geometric constraints within the Lucinidae (Bivalvia), p. 49-72. In: Experimental Approaches to Understanding Fossil Organisms. Springer Netherlands.
Megerle von Mühlfeld, J.K. 1811. Entwurf eines neuen System’s der Schalthiergehäuse. Gesellschaft Naturforschender Freunde zu Berlin, Magazin 5: 38-72.
Monari, S. 2003. A new genus and species of fimbriid bivalve from the Kimmeridgian of the western Pontides, Turkey, and the phylogeny of the Jurassic Fimbriidae. Palaeontology 46: 857-884.
Morton, B. 1979. The biology and functional morphology of the coral-sand bivalve Fimbria fimbriata (Linnaeus, 1758). Records of the Australian Museum 32: 389-420.
Taylor, J.D. and Glover, E.A. 2006. Lucinidae (Bivalvia)–the most diverse group of chemosymbiotic molluscs. Zoological Journal of the Linnean Society 148: 421-438.
