Hong Kong Coral Gall Crab

Neotroglocarcinus hongkongensis

Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Decapoda
Family: Cryptochiridae
Genus: Neotroglocarcinus
Species: Neotroglocarcinus hongkongensis

The Hong Kong coral gall crab (Neotroglocarcinus hongkongensis) is a tiny crab that lives in a pit inside living stony coral, named after the place it was first described. Despite the name, it is widespread across the Indo-West Pacific.

Females measure only a few millimetres and live permanently inside their coral dwelling, feeding on mucus and food particles, while the smaller males move between corals. This species is mostly associated with faviid-type massive corals.

In the Philippines it lives hidden on coral reefs, where its small, crescent-shaped openings can be spotted on coral heads by divers who know what to look for.

Photo: Gregor Bailar, CC BY 4.0, via iNaturalist