Tridacna gigas   Linnaeus,  1758 (Clam)
Organism information awaits expert curation
Class: Bivalvia
Order:Euheterodonta incertae sedis

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Size: 137 cm in length

Color: Exterior of shell off-white, often strongly encrusted with marine growths. Interior porcelaneous white. Dorsally exposed mantle area of living specimens yellowish brown to olive green, with numerous, small, brilliant blue-green rings.

It is the largest known species of bivalve. It is suboval to fan shaped in outline, moderately to strongly inflated and with small to nearly closed byssal orifice. Valves are moderately thin in small specimens to extremely heavy and thick in large individuals. Dorsal shell margins are broadly fan shaped in outline, undulate, with series of 4-5 usually rather sharply pointed, medially projecting interdigitating processes representing extremities of rib interstices, often crenulate at their edges. Hinge line is somewhat longer than half the length of shell. Hinge teeth become obsolete in large individuals. A single, oblong cardinal tooth is present in each valve, 2 elongate posterior lateral teeth in right valve and 1 in the left. Umbos are directed posteromedially. Ventral margin is nearly straight, but may be slightly concave in region of byssal orifice. Pallial line is entire, wide and roughened.

They reproduce sexually via broadcast spawning. They expel sperm and eggs into the sea. Fertilization takes place in open water and is followed by a planktonic larval stage. The larvae (veligers) must swim and feed in the water column until they are sufficiently developed to settle on a suitable substrate, usually sand or coral rubble, and begin their adult life as a sessile clam.

It obtains the bulk of its nutrition from photosymbionts living within its tissues. These are unicellular algae (often called zooxanthellae) that are farmed by the mollusk host in much the same way that corals do. In some Tridacna gigas, the zooxanthellae have been shown to provide 90% of the carbon chains metabolized. This is an obligate association for the clam and it will die in the absence of the zooxanthellae, or if kept in the dark.

Synonym (s)

Common Name (s)
Economic Importance and Threats
Importance:  Commercial
(Fisheries, aquarium. Exploited for its meat and shell.)
Cultured:  Yes

Habitat:  Reef Associated,Demersal,Sandy
Trophic Level:  Consumer
Prey:  Phytoplankton, zooplankton
IUCN Status:  Vulnerable


Literature Source(s)
  • Kittiwattanawong, K (2001) Records of extinct Tridacna gigas in Thailand Phuket Marine Biological Center Special Publication 25(2) 461-463 Available at - ZOOR13800055967
  • Rosewater, J (1965) The family Tridacnidae in the Indo Pacific Indo-Pacific Mollusca Academy of Natural Sciences of Philadelphia, Pennsylvania 1(6) 347-408 Available at - NIO, Goa
  • Myers, P; Espinosa, R; Parr, CS; Jones, T; Hammond, GS and Dewey, TA (2006) Animal diversity web Available at -
  • Sealifebase Available at -
  • Society for the Management of European Biodiversity Data (2009) World Register of Marine Species (WoRMS) Available at -
  • Poutiers, JM (1998) Bivalves FAO species identification guide for fishery purposes. The living marine resources of the western central Pacific. Volume 1: Seaweeds, corals, bivalves and gastropods FAO, Rome 1 686 pp Available at -
  • Available at -

Page last updated on:2010-06-14

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