THE ANIMAL FILES

Giant clam

Tridacna gigas

A clam can host part of its own food supply.

The giant clam combines filter feeding with a close association with photosynthetic algae. Its fleshy mantle carries symbionts and light-sensitive spots. Sunlight and suspended food therefore reach the animal through different routes.[1]

Follow the evidence ↓
Giant clam
Image: Nhobgood Nick Hobgood · Commons · CC BY-SA 3.0
Algae in the mantle
Photosynthetic symbionts contribute nutrients.[1]
Filtering also matters
Filter feeding remains part of nutrition.[1]
Detecting changing light
Mantle eyespots respond to changing illumination.[1]

Algae in the mantle

The mantle contains zooxanthellae, algae that use light. The clam supplies a living environment and materials used by its symbionts, while their photosynthesis contributes to its nutrition. This is an association between different organisms rather than a clam becoming a plant.[1]

Filtering also matters

Waterborne food supplements the algal partnership. In studies comparing different sizes of clams, smaller animals obtained a larger share of the carbon needed for growth and respiration from filter feeding. The balance between the two routes changes as the animal grows.[1]

Detecting changing light

Numerous small eyespots line the mantle edge. They detect dimming, changes in light direction or moving objects, contributing to partial shell-closing responses. That sensitivity should not be described as a human-like visual scene or detailed object recognition.[1]

A COMMON MIX-UP

Does hosting photosynthetic algae make a clam a plant?

No. It is an animal living with algal symbionts and also filter-feeding.[1]

TRY A LITTLE REASONING

Why would a fixed 'all food comes from sunlight' description be wrong?

Reveal the explanation

The animal also filters food, and the balance between feeding routes varies.[1]

Sources & editorial notes

Adapted and translated from the cited Wikipedia revisions, with source-linked reasoning. Image credit and licence are listed separately above.

Adapted and translated from Wikipedia contributors; exact revisions are linked below. CC BY-SA 4.0

  1. Wikipedia contributors — Giant clam (cited revision)
  2. NCBI Taxonomy — Tridacna gigas

Last fact check:

One discovery leads to another

Spectacle case pearly musselA river mussel begins with a fish connection.Cumberlandia monodonta ↗Pacific oysterA drifting larva becomes a permanently attached oyster.Magallana gigas ↗Roman snailThe shell has a doorway—and sometimes a temporary seal.Helix pomatia ↗