These clams were known to indigenous peoples of East Asia for thousands of years and the Venetian scholar and explorer Antonio Pigafetta documented them in a journal as early as 1521.

One of a number of large clam species native to the shallow coral reefs of the South Pacific and Indian oceans, they may weigh more than 200 kilograms (440 lb), measure as much as 120 cm (47 in) across, and have an average lifespan in the wild of more than 100 years.

[8] The creature's mantle tissues act as a habitat for the symbiotic single-celled dinoflagellate algae (zooxanthellae) from which the adult clams get most of their nutrition.

By day, the clam opens its shell and extends its mantle tissue so that the algae receive the sunlight they need to photosynthesise.

Adult T. gigas are the only giant clams unable to close their shells completely, allowing part of the brownish-yellow mantle to remain visible.

[9] Similar to coral matrices composed of calcium carbonate, giant clams grow their shells through the process of biomineralization, which is very sensitive to seasonal temperature.

[12][13] Each one consists of a small cavity containing a pupil-like aperture and a base of 100 or more photoreceptors sensitive to three different ranges of light, including UV, which may be unique among molluscs.

[17][18] The clams cultivate algae in a special circulatory system that enables them to keep a substantially higher number of symbionts per unit of volume.

[6]: 46  This flexibility in reproduction reduces the burden of finding a compatible mate, while simultaneously doubling the number of offspring produced.

Incoming water passes chemoreceptors situated close to the incurrent syphon that transmit the information directly to the cerebral ganglia, a simple form of brain.

[6]: 47 Detection of SIS stimulates the giant clam to swell its mantle in the central region and to contract its adductor muscle.

[24] The ability for Tridacna to grow to such large sizes with fleshy mantles that extend beyond the edges of their shells is considered to be the result of total reorganization of bivalve development and morphology.

Sir Yonge suggested and maintained for many years that the visceral-pedal ganglia complex rotate 180 degrees relative to the shell, requiring that they develop and evolve independently.

Versions of the U.S. Navy Diving Manual even gave detailed instructions for releasing oneself from its grasp by severing the adductor muscles used to close its shell.

[28] In an account of the discovery of the Pearl of Lao Tzu, Wilburn Cobb said he was told that a Dyak diver was drowned when the Tridacna closed its shell on his arm.

[29] In reality, the slow speed of their abductor muscle contraction and the need to force water out of their shells while closing, prevents them from trapping a human.

[27] While giant clams do live a long time and may serve as a bio-metric for historic climatic conditions, their large size is more likely associated with rapid growth.

[34] Restocked individuals in the Philippines have successfully dispersed their own spawned larvae to at least several hundred meters away after only ten years.