Tridacna
Encyclopedia
Tridacna is a genus
of large and gigantic saltwater clam
s, marine
bivalve mollusks in the subfamily Tridacninae, the giant clams. They have heavy shells, fluted with 4–6 folds. Mantle
is brightly coloured. They inhabit shallow waters of coral reef
s in warm seas of the Indo-Pacific
region. These clams are popular in marine aquaria
, and in some areas, such as the Tulo, Calamba City, Laguna (Bahay nina Lourdes at Isabel kasama pa si Audrey) in Philippines
, members of the genus are farmed for the marine aquarium trade. They live in symbiosis with photosynthetic algae
(zooxanthella
e). Some species are used as seafood
.
Subgenus Tridacna (Tridacna)
Subgenus Tridacna (Chametrachea)
An alternative older classification recognises a third subgenus Persikima containing T. derasa and T. tevoroa.
Recent biochemical studies have suggested that there may exist morphologically indistinct cryptic species.
coral reef
benthic communities in shallower waters. They live in symbiosis
with photosynthetic dinoflagellate
algae (Symbiodinium) that grow in the mantle
tissues 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. They get most (70-100%) of their nutrients from the algae and the rest from filter feeding. 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.
. 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.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of large and gigantic saltwater clam
Clam
The word "clam" can be applied to freshwater mussels, and other freshwater bivalves, as well as marine bivalves.In the United States, "clam" can be used in several different ways: one, as a general term covering all bivalve molluscs...
s, marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...
bivalve mollusks in the subfamily Tridacninae, the giant clams. They have heavy shells, fluted with 4–6 folds. Mantle
Mantle (mollusc)
The mantle is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of flaps well beyond the visceral mass itself.In many, but by no means all, species of molluscs, the epidermis of the mantle secretes...
is brightly coloured. They inhabit shallow waters of coral reef
Coral reef
Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...
s in warm seas of the Indo-Pacific
Indo-Pacific
The Indo-Pacific is a biogeographic region of the Earth's seas, comprising the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the seas connecting the two in the general area of Indonesia...
region. These clams are popular in marine aquaria
Marine aquarium
A marine aquarium is an aquarium that keeps marine plants and animals in a contained environment. Marine aquaria are further subdivided by hobbyists into fish only , fish only with live rock , and reef aquaria. Fish only tanks often showcase large or aggressive marine fish species and generally...
, and in some areas, such as the Tulo, Calamba City, Laguna (Bahay nina Lourdes at Isabel kasama pa si Audrey) in Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
, members of the genus are farmed for the marine aquarium trade. They live in symbiosis with photosynthetic algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
(zooxanthella
Zooxanthella
Zooxanthellae are flagellate protozoa that are golden-brown intracellular endosymbionts of various marine animals and protozoa, especially anthozoans such as the scleractinian corals and the tropical sea anemone, Aiptasia....
e). Some species are used as seafood
Seafood
Seafood is any form of marine life regarded as food by humans. Seafoods include fish, molluscs , crustaceans , echinoderms . Edible sea plants, such as some seaweeds and microalgae, are also seafood, and are widely eaten around the world, especially in Asia...
.
Systematics and phylogeny
The genus contains two subgenera and the following species:Subgenus Tridacna (Tridacna)
- Tridacna derasa (Röding, 1798)
- Tridacna gigasGiant clamThe giant clam, Tridacna gigas , is the largest living bivalve mollusc. T. gigas is one of the most endangered clam species. It was mentioned as early as 1825 in scientific reports...
Linnaeus, 1758 - Tridacna tevoroa Lucas, Ledua & Braley, 1990
Subgenus Tridacna (Chametrachea)
- Tridacna costataTridacna costataTridacna costata is a newly discovered species of giant clam. It lives in the shallow waters of the Red Sea. Fossil evidence suggests the stocks of these giant clams began crashing some 125,000 years ago, during the last interval between glacial periods....
Richter, Roa-Quiaoit, Jantzen, Al-Zibdah, Kochzius, 2008 - Tridacna crocea Lamarck, 1819
- Tridacna maxima Röding, 1798( =Tridacna elongata)
- Tridacna rosewateriTridacna rosewateriTridacna rosewateri is a species of marine bivalve in the Tridacnidae family. It is endemic to Mauritius....
Sirenho & Scarlato, 1991 - Tridacna squamosaTridacna squamosaTridacna squamosa, colloquially known as the fluted giant clam, is one of a number of large clam species native to the shallow coral reefs of the South Pacific and Indian oceans. It is distinguished by the presence of large leaf-like fluted edges on its shell called 'scutes' and a byssal opening...
Lamarck, 1819
An alternative older classification recognises a third subgenus Persikima containing T. derasa and T. tevoroa.
Recent biochemical studies have suggested that there may exist morphologically indistinct cryptic species.
Ecology and behaviour
Tridacna clams are common inhabitants of Indo-PacificIndo-Pacific
The Indo-Pacific is a biogeographic region of the Earth's seas, comprising the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the seas connecting the two in the general area of Indonesia...
coral reef
Coral reef
Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...
benthic communities in shallower waters. They live in symbiosis
Symbiosis
Symbiosis is close and often long-term interaction between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens...
with photosynthetic dinoflagellate
Dinoflagellate
The dinoflagellates are a large group of flagellate protists. Most are marine plankton, but they are common in fresh water habitats as well. Their populations are distributed depending on temperature, salinity, or depth...
algae (Symbiodinium) that grow in the mantle
Mantle (mollusc)
The mantle is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of flaps well beyond the visceral mass itself.In many, but by no means all, species of molluscs, the epidermis of the mantle secretes...
tissues 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. They get most (70-100%) of their nutrients from the algae and the rest from filter feeding. 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.
Artistic Use
Over a hundred examples of carved Tridacna shells have been found in archaeological expedititions 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 PhoeniciaPhoenicia
Phoenicia , was an ancient civilization in Canaan which covered most of the western, coastal part of the Fertile Crescent. Several major Phoenician cities were built on the coastline of the Mediterranean. It was an enterprising maritime trading culture that spread across the Mediterranean from 1550...
. 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.