Үлкен жүрек қабыршақтар: Tridacna туысы

Genus of bivalves

Tridacna is a genus of large saltwater clams, marine bivalve molluscs in the subfamily Tridacninae, the giant clams. Many Tridacna species are threatened. They have heavy shells, fluted with 4 to 6 folds. The mantle is often brightly coloured. They inhabit shallow waters of coral reefs in warm seas of the Indo Pacific region. These clams are popular in marine aquaria, and in some areas, such as the Philippines, members of the genus are farmed for the marine aquarium trade. They live in symbiosis with photosynthetic algae (zooxanthellae). Some species are eaten by humans. All species in the genus Tridacna are protected under CITES Appendix II.

The name Tridacna arises from Greek words tri, meaning three, and dacno, meaning bite. In the Ancient Roman text Natural History, Pliny the Elder explained the nomenclature comes from the fact that "they are so large as to require three bites in eating them.”

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.

Tridacna clams are common inhabitants of Indo Pacific coral reef benthic communities in shallower waters. They live in symbiosis with photosynthetic dinoflagellate algae (Symbiodinium) that grow in the mantle tissues. Light penetrates the mantle through small lens like structures called ocelli. 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. They are being sustainably farmed in some areas, both for the seafood market in some Asian countries and for the aquarium trade. Tridacna clams can produce large white pearls with an undulating, porcelain like surface, 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.

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.