大砗磲（学名：Tridacna gigas），又称巨蚌、库氏砗磲，是最大型的双壳贝类动物。栖息于南太平洋和印度洋的珊瑚礁。最重可达200公斤，壳宽可达1.2公尺。

在传说中，巨蚌常被误解为“杀人蚌”或“食人蚌”，《美国海军潜水手册》甚至曾经详述如果被巨蚌所夹住要如何切断其内收肌脱困。然而事实上巨蚌并不特别有侵略性或特别危险，更不是肉食性贝类。巨蚌的确有能力合起双壳，但这是一种防御性行为。而且因为受到刺激关闭，牠必须先喷水，排出滤食中的海水，时间足足有10几秒之多，并非陷阱式的夹合。并没有任何记录能证明有过任何人类曾经因这种方式被受困。 **又叫 五爪贝

The giant clam (Tridacna gigas), known as pā’ua in Cook Islands Māori, is a clam that is the largest living bivalve mollusk.

Tridacna gigas is one of the most endangered clam species. Antonio Pigafetta documented these in his 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 can 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 over 100 years. They are also found off the shores of the Philippines, where they are called "taklobo", and in the South China Sea in the coral reefs of Sabah (Malaysian Borneo). Tridacna gigas lives in flat coral sand or broken coral and can be found at depths of as much as 20 m (66 ft). Its range covers the Indo-Pacific, but populations are diminishing quickly and the giant clam has become extinct in many areas where it was once common. Tridacna maxima has the largest geographical distribution among giant clam species; it can be found off high- or low-elevation islands, in lagoons or fringing reefs. Its rapid growth rate is likely due to its ability to cultivate algae in its body tissue.