Animal · Australia, Philippines, Indonesia
Giant clam
Tridacna gigas — the name this animal has in the language scientists everywhere share.
The giant clam is the biggest shellfish in the sea: its two shells together span more than a metre and weigh as much as three grown-ups. As a youngster it settles on a reef and then stays in that same spot for a hundred years or more.
Picture credit: Charles J. Sharp (CC BY-SA 4.0) · Wikimedia Commons
Where does the giant clam live?
Home: on shallow, sunny coral reefs of the tropical Indo-Pacific.
In the wild it lives in these countries: Australia, the Philippines, Indonesia, Papua New Guinea, the Solomon Islands, Fiji, Palau, Malaysia.
Conservation status from the IUCN: critically endangered.
The short profile
Fully grown: up to 137 cm across. It weighs about 200 kilograms. On the menu: tiny creatures it filters out of the water.
The story behind it
The colourful, wavy flesh you see between the open shells is the mantle, and it is packed with tiny algae. The clam gives the algae a safe, sunlit place to live, and the algae hand back sugar: about two thirds of the clam's food is made this way. The rest it filters out of the water, drawing seawater in and sieving plankton from it. Old stories call it the killer clam that traps a diver's leg, but that is a legend. Its shells cannot even close all the way, and the muscle pulls them together far too slowly to catch anyone. The real danger runs the other way: in a century the species has lost about 84 percent of its numbers, and in 2024 the IUCN listed it as critically endangered.
Find it on the globe
Giant clam is there as a tiny animated figure that breathes and looks around. From far away the planet is only a blue ball; detail arrives as you zoom in, and this one appears once you are close enough. Open it on the globe.
It sits at its real coordinates, not near them — the same numbers listed in the facts above. Switch off the layer for this kind of place and it disappears again; the buttons for that are down the right-hand edge.
Questions children ask
How big does a giant clam get?
The largest measured shell was 137 cm across and the living animal weighed about 250 kg, heavier than three grown-ups together.
Where does the giant clam live?
On sunny coral reefs of the Indo-Pacific, from the Philippines and Indonesia to Australia and Fiji, down to about 20 m. It needs light for its algae.
Can a giant clam trap a diver?
No. Its shells never close completely and the muscle moves far too slowly, so the killer clam is a story, not a fact.
Where these numbers come from
Every figure on this page was checked against public reference sources before publication. Where sources genuinely disagree, the text says so.
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