Many bivalves have a powerful abductor muscle that they use to tightly close their valves, thus protecting themselves from predators. The smaller species, which live anchored to the substrate, do not exert enough pressure to hold a diver and force him to stay underwater. However, one of these creatures is often cited in legends about drowned divers. It is Tridacna gigas , better known as the giant clam; the largest bivalve in the world, capable of reaching 150 centimeters in length and three hundred kilos in weight .
Given their size, their shells have sometimes been used as a baptismal font, a use that Jules Verne curiously cited in 20,000 leagues of underwater travel . However, despite their bad reputation, the so-called giant taclobos do not pose a danger to people, and no deaths related to them have been documented .
In addition to Tridacna gigas , seven species have been described within this genus, native to the Indian Ocean, the Pacific or the Red Sea, where they live in the vicinity of the reefs. They have a particularity compared to other clams: they have zooxanthellae in their tissues, that is, dinoflagellate algae like those that inhabit corals.
However, while in the latter the microorganisms live inside the cells, in the taclobos they do so in channels located between them. The two beings maintain a symbiotic relationship, in such a way that the microalgae feed on the organic waste secreted by the clam, and this, for its part, takes advantage of the sugars that the former produce in photosynthesis.
Giant clams are hermaphrodites ; the young specimens are male, but as they develop, female organs appear, and they present those of both sexes at maturity. They cannot fertilize themselves, since both sperm and eggs are released at different times. They can live for more than a century.
Image: Rick Hankinson via Wikimedia / CC
