Bird's Nest Coral Crab

Trapezia guttata

Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Decapoda
Family: Trapeziidae
Genus: Trapezia
Species: Trapezia guttata

The bird's nest coral crab (Trapezia guttata) is a small guard crab that lives among the branches of Seriatopora and other branching corals, defending its host against predators. It has a smooth, pale body and claws, often with small reddish spots along the margins.

Usually around 1-2 cm across, it lives in pairs within a single coral colony. In exchange for shelter and the coral's mucus and fat bodies, the crab pinches and chases away crown-of-thorns starfish, snails and other coral eaters, and it helps clear sediment from the coral.

Bird's nest corals on shallow reefs in the Philippines often host these crabs. Peering carefully into the branches will usually reveal one or two guard crabs watching back.

Photo: Daniel Eisenhauer, CC BY 4.0, via iNaturalist