Tridacninae, common name the giant clams, is a taxonomic subfamily of very large saltwater clams, marine bivalve molluscs in the family Cardiidae, the cockles.
Description This subfamily contains the largest living bivalve species, including Tridacna gigas, the giant clam. They have heavy shells, fluted with 4–6 folds. The mantle is usually brightly colored. They inhabit coral reefs in warm seas in the Indo-Pacific region. Most of these clams live in symbiosis with photosynthetic dinoflagellates (zooxanthellae), a type of photosymbiosis.
Systematics Sometimes the giant clams are still treated as a separate family Tridacnidae,WoRMS. (2009). Tridacnidae. Accessed through the World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=196336 on 2009-01-10. but modern phylogenetic analyses included them in the family Cardiidae as a subfamily.Schneider, J. Phylogeny of cardiid bivalves (cockles and giant clams): revision of the Cardiinae and the importance of fossils in explaining disjunct biogeographical distributions. Zoological Journal of the Linnean Society, 2002,136, 321–369Keys, J.L., Helay, J.M. Relevance of Sperm Ultrastructure to the Classification of Giant Clams (Mollusca, Cardioidea, Cardiidae, Tridacnidae)(in: Harper et al., (Eds) The Evolutionary Biology of the Bivalvia, Geological Society Special Publication No 177, 2000) Two recent genera and eight species are known: Hippopus—2 species Tridacna—10 species Recent genetic evidence has shown them to be monophyletic sister taxa.Schneider, J.A., and O´Foighil, D. Phylogeny of Giant Clams (Cardiidae: Tridacnidae) Based on Partial Mitochondrial 16S rDNA Gene Sequences. Molecular Phylogenetics and Evolution Vol. 13, No. 1, October, pp. 59–66, 1999
Human relevance In some areas, such as the Philippines, smaller members of the subfamily are farmed to supply the marine aquarium trade and food trade towards east Asia. All species in the Tridacninae family are protected under CITES Appendix II meaning international trade requires CITES permits to be granted.
Evolutionary history Tridacinae originated in Western Europe during the Eocene, expanding eastwards towards Arabia by the Oligocene, and becoming established in its modern distribution in the Indo-Pacific during the Pliocene-Pleistocene.
References
External links Description