---
title: Giant Clam (Tridacna maxima)
scientific_name: Tridacna maxima
common_name: Giant Clam
taxon: Clams
conservation_status: LC - Least Concern
published: 2023-12-29T10:28:42.817Z
updated: 2026-08-14T11:57:50.831Z
tags: Giant Clam, Tridacna maxima, Clams, Red Sea, Marine Life, Diving
url: https://redseacreatures.com/taxon/invertebrate/molluscs/clams/giant-clam
---

# Giant Clam (*Tridacna maxima*)

## Quick facts

- **Group:** Clams (*Bivalvia*)
- **Size:** up to 35 cm
- **Depth:** 0-20 m
- **Max age:** 100 yrs
- **Diet:** Photosynthetic
- **Activity:** Diurnal
- **Rarity:** Common
- **Habitat:** Bored into coral rock on shallow reef flats
- **Reproduction:** Broadcast spawner, Protandrous hermaphrodite
- **CITES:** Appendix II
- **Conservation status:** LC - Least Concern

## How to recognise it

- shell sunk into the rock, only the mantle edge visible
- mantle in electric blue, green or gold with fine speckling
- shell ribs low, without the tall flutes of its fluted relative
- shell to 35 cm

The clam whose mantle is the blue-green thing everyone photographs on a shallow reef flat, wedged into the rock so deep that only the opening shows. Thirty-five centimeters (14 in) of shell, most of it out of sight.

The name misleads: *maxima* is the smallest of the giant clams, not the largest. It earns its place another way - it is the most widespread of them, and the one that colonizes hard reef rock by grinding itself in. A young clam settles on the surface and rasps and rocks its way down over years until the shell sits in a socket of its own making, safe from anything that would pry it out.

Being embedded costs it something. It cannot close fully around a mantle that has to stay spread in the light, and the animals living inside that mantle are the reason: symbiotic algae that supply most of its food. In return the clam gives them a lit, protected greenhouse and pumps water past them all day.

Because they are permanently open, they are also easy to take, and this is the clam that vanished first around inhabited coasts. CITES Appendix II covers the whole family. On the reef the rule is simple: they respond to a shadow by closing, and repeatedly making one close costs the animal energy it spent all day collecting.

## Also known as

- **English:** elongate clam, elongated clam, small giant clam
- **French:** Bénitier
- **German:** Kleine Riesenmuschel, Längliche Riesenmuschel
- **Portuguese:** Bivalve
- **Japanese:** シラナミガイ
- **Chinese:** 長硨磲蛤
- **Russian:** Гигантская тридакна (Тридакна большая)

## Scientific synonyms

- *Tridachnes maxima* Röding, 1798
- *Tridacna (Chametrachea) maxima* (Röding, 1798)
- *Tridacna acuticostata* G. B. Sowerby III, 1912
- *Tridacna compressa* Reeve, 1862
- *Tridacna detruncata* Bianconi, 1869
- *Tridacna elongata* Lamarck, 1819
- *Tridacna fossor* Hedley, 1921
- *Tridacna imbricata* (Röding, 1798)
- *Tridacna lanceolata* G. B. Sowerby II, 1884
- *Tridacna maxima var. fossor* Hedley, 1921
- *Tridacna mutica* Lamarck, 1819
- *Tridacna reevei* Hidalgo, 1903
- *Tridacna rudis* Reeve, 1862

## Range

Indian Ocean, Republic of Mauritius

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*Source: [Red Sea Creatures](https://redseacreatures.com/taxon/invertebrate/molluscs/clams/giant-clam)*
*Updated: August 14, 2026*