Tridacninae,

common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often contrast ...

, the giant clams, is a

taxonomic Taxonomy is the practice and science of categorization or classification. A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...

subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end subfamily botanical names with "-oideae", and zoologi ...

of very large saltwater clams,

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

s in the family

Cardiidae A cockle is an edible marine bivalve mollusc. Although many small edible bivalves are loosely called cockles, true cockles are species in the family Cardiidae. MolluscaBase eds. (2022). MolluscaBase. Cardiidae Lamarck, 1809. Accessed through: W ...

, the cockles.

Description

This subfamily contains the largest living bivalve species, including ''

Tridacna gigas The giant clams are the members of the clam genus ''Tridacna'' that are the largest living bivalve mollusks. There are actually several species of "giant clams" in the genus ''Tridacna'', which are often misidentified for ''Tridacna gigas'', th ...

'', the

giant clam The giant clams are the members of the clam genus ''Tridacna'' that are the largest living bivalve mollusks. There are actually several species of "giant clams" in the genus ''Tridacna'', which are often misidentified for ''Tridacna gigas'', th ...

. 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 The Indo-Pacific is a vast biogeographic region of Earth. In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asia, it comprises the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the ...

region. Most of these clams live in

symbiosis Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

with photosynthetic

dinoflagellate The dinoflagellates (Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are ...

s (

zooxanthella Zooxanthellae is a colloquial term for single-celled dinoflagellates that are able to live in symbiosis with diverse marine invertebrates including demosponges, corals, jellyfish, and nudibranchs. Most known zooxanthellae are in the genus ''Symbi ...

e).

Systematics

Sometimes the giant clams are still treated as a separate family Tridacnidae, but modern

phylogenetic analyses In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

included them in the family

as a subfamily. Two recent genera and eight species are known: * ''

Hippopus ''Hippopus'' is a genus of large tropical saltwater clams, marine bivalve molluscs in the subfamily Tridacninae, the giant clam subfamily, of the family Cardiidae A cockle is an edible marine bivalve mollusc. Although many small edible bi ...

''—2 species * ''

Tridacna ''Tridacna'' is a genus of large saltwater clams, marine bivalve molluscs in the subfamily Tridacninae, the giant clams. They have heavy shells, fluted with 4 to 6 folds. The mantle is brightly coloured. They inhabit shallow waters of coral re ...

''—10 species Recent genetic evidence has shown them to be

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

sister taxa In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...

. Image:Hippopus hippopus Vanuatu 01.jpg, Live ''

Hippopus hippopus ''Hippopus hippopus'', also known as the Horse Hoof clam and Strawberry clam, is a species of giant clam in the Family Tridacna and the genus ''Hippopus''. ''Hippopus'' is a delicacy in many Southeast Asian countries due to its high quality meat. ...

'' (

Vanuatu Vanuatu ( or ; ), officially the Republic of Vanuatu (french: link=no, République de Vanuatu; bi, Ripablik blong Vanuatu), is an island country located in the South Pacific Ocean. The archipelago, which is of volcanic origin, is east of no ...

) Image:Tridacna squamosa Réunion.jpg, Live ''

Tridacna squamosa ''Tridacna squamosa'', known commonly as the fluted giant clam and scaly clam, is a species of bivalve in the family Cardiidae. MolluscaBase eds. (2022). MolluscaBase. Tridacna squamosa Lamarck, 1819. Accessed through: World Register of Marine S ...

'' (

la Réunion LA most frequently refers to Los Angeles, the second largest city in the United States. La, LA, or L.A. may also refer to: Arts and entertainment Music * La (musical note), or A, the sixth note * "L.A.", a song by Elliott Smith on ''Figure ...

) Image:Hippopus hippopus.jpg, ''

'' shells Image:Doopvontschelp grootste ter wereld.jpg, Giant clam (''

'') shell

Human relevance

In some areas, such as the

Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...

, smaller members of the subfamily are farmed to supply the

marine aquarium A marine aquarium is an aquarium that keeps ocean, marine plants and animals in a contained environment. Marine aquaria are further subdivided by hobbyists into fish only (FO), fish only with live rock (FOWLR), and reef aquarium, reef aquaria. Fi ...

trade and food trade towards east Asia. All species in the Tridacninae family are protected under

CITES Appendix II CITES (shorter name for the Convention on International Trade in Endangered Species of Wild Fauna and Flora, also known as the Washington Convention) is a multilateral treaty to protect endangered plants and animals from the threats of interna ...

meaning international trade requires CITES permits to be granted.

Evolutionary history

Tridacinae originated in Western Europe during the

Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...

, expanding eastwards towards

Arabia The Arabian Peninsula, (; ar, شِبْهُ الْجَزِيرَةِ الْعَرَبِيَّة, , "Arabian Peninsula" or , , "Island of the Arabs") or Arabia, is a peninsula of Western Asia, situated northeast of Africa on the Arabian Plate. ...

by the

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

, and becoming established in its modern distribution in the Indo-Pacific during the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

References

External links

Description
Protostome subfamilies Extant Eocene first appearances {{Bivalve-stub