Tridacna

The genus contains two subgenera and the following species:[4][5]

• Tridacna lorenzi Monsecour, 2016 -- Mascarene region
• Tridacna noae (Röding, 1798) -- China sea

Subgenus Tridacna (Tridacna)

• Tridacna derasa (Röding, 1798) -- Western Pacific
• Tridacna gigas (Linnaeus, 1758) -- Tropical Indo-Pacific
• Tridacna mbalavuana Ladd, 1934 (= Tridacna tevoroa Lucas, Ledua & Braley, 1990) -- Fidji, Tonga

Subgenus Tridacna (Chametrachea)

• Tridacna squamosina Sturany, 1899 (= Tridacna costata Roa-Quiaoit, Kochzius, Jantzen, Al-Zibdah & Richter 2008) -- Red Sea
• Tridacna crocea Lamarck, 1819 -- Western Pacific
• Tridacna maxima Röding, 1798 ( =Tridacna elongata) -- Tropical Indo-Pacific
• Tridacna rosewateri Sirenho & Scarlato, 1991 -- Mascarene region
• Tridacna squamosa Lamarck, 1819 -- Tropical Indo-Pacific

Wikimedia Commons has media related to Tridacna.

An alternative older classification recognises a third subgenus Persikima containing T. derasa and T. mbalavuana.[6] Recent biochemical studies have suggested that there may exist morphologically indistinct cryptic species.[2][7]

Compared to other clams, the soft mantle that secretes the shell is greatly expanded. The clams even have small lens-like structures called ocelli through which light penetrates.[8]

One of the two clam stoups of the Église Saint-Sulpice in Paris, carved by Jean-Baptiste Pigalle.

Tridacna clams are common inhabitants of Indo-Pacific coral reef benthic communities in shallower waters.[9] They live in symbiosis with photosynthetic dinoflagellate algae (Symbiodinium) that grow in the mantle tissues.[10] Light penetrates the mantle through small lens-like structures called ocelli.[8] They are sessile in adulthood. 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 get most (70-100%) of their nutrients from the algae and the rest from filter feeding.[11] When disturbed, the clam closes its shell. The popular opinion that they pose danger to divers who get trapped or injured between the closing sharp-edged shell is not very real, as the closing reaction is quite slow. Their large size and easy accessibility has caused overfishing and collapse of the natural stocks in many places and extirpation in some of the species.[12] They are being sustainably farmed in some areas,[13] both for the seafood market in some Asian countries and for the aquarium trade.[14]

Tridacna clams can produce large white pearls with an undulating, porcelain-like surface,[15] which may be described as "non-nacreous pearls". The "Pearl of Lao Tzu", also known as the "Pearl of Allah", is the world's largest pearl weighing 6.4 kilogrammes; it was said to have been found inside a Tridacna gigas by a Filipino diver in 1934.[16][17]

Over a hundred examples of carved Tridacna shells have been found in archaeological expeditions from Italy to the Near East. Similar in artistic style, they were probably produced in the mid-seventh century, made or distributed from the southern coast of Phoenicia. The backs and interior perimeters of the shells show animal, human, and floral motifs, while the interiors typically show recumbent sphinxes. The umbo of the shell is in the shape of a human female or bird's head. They were probably used to store eye cosmetics.[18]

• 
  Tridacna crocea
• 
  Tridacna derasa
• 
  Tridacna gigas
• 
  Tridacna maxima
• 
  Tridacna squamosa
• 
  Tridacna squamosina

• Murphy, Richard C. (2002). Coral Reefs: Cities Under The Sea. Princeton, New Jersey: The Darwin Press. ISBN 978-0-87850-138-0.CS1 maint: ref=harv (link)
• How to Care for Tridacnid Clams FishChannel.com