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The maxima clam has the largest geographical distribution among giant clam species; it may be found off high- or low-elevation islands, in lagoons or fringing reefs. [7] Its rapid growth rate is likely due to its ability to cultivate algae in its body tissue. [6]: 10 Although larval clams are planktonic, they become sessile in adulthood. [8]
The shell of the clam ranges from 15 centimetres (6 in) to over 20 centimetres (8 in) in length, but the extremely long siphons make the clam itself much longer than this: the "shaft" or siphons alone can be 1 metre (3 ft 3 in) in length. The geoduck is the largest burrowing clam in the world. [3]
By day, the clams spread out their mantle so that the algae receive the sunlight they need to photosynthesize, whereas the colour pigments protect the clam against excessive light and UV radiation. Adult clams can get most (70–100%) of their nutrients from the algae and the rest from filter feeding. [12] When disturbed, the clam closes its shell.
Sometimes the giant clams are still treated as a separate family Tridacnidae, [1] but modern phylogenetic analyses included them in the family Cardiidae as a subfamily. [2] [3] 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. [4]
The Registry of World Record Size Shells is a conchological work listing the largest (and in some cases smallest) verified shell specimens of various marine molluscan taxa.A successor to the earlier World Size Records of Robert J. L. Wagner and R. Tucker Abbott, it has been published on a semi-regular basis since 1997, changing ownership and publisher a number of times.
Image credits: bglickstein #3. I noticed this when visiting museums, looking at old paintings: hands are often ‘hidden’, covered by flowers, clothing or they disappear in the shadows.
One of the world's largest clam fossils (187 cm), a Sphenoceramus steenstrupi specimen from Greenland in the Geological Museum in Copenhagen. Maxima clam, Tridacna maxima. Edible: Ark clams, family Arcidae (most popular in Indonesia and Singapore) Atlantic jackknife clam: Ensis directus; Atlantic surf clam: Spisula solidissima
The southern giant clam is a popular food item and aquarium species, and has therefore been hunted extensively throughout its natural habitat. [6] However, specimens traded today tend to be the result of aquaculture farms rather than wild-caught individuals, because the southern giant clam was one of the first clams to be bred commercially. [6]