### Identification Look for a tiny, porcelain-like gem tucked deep within the labyrinthine branches of *Acropora* corals. *Tetralia glaberrima*, commonly known as the Smooth Coral Crab, is small—rarely exceeding 1.5 cm in width—with a distinctively flattened, trapezoidal carapace. While its body is typically a pale cream or translucent tan, the defining field mark is its "bandit mask": a crisp, dark brown or black line running across the frontal margin between its eyes. Unlike the similar *Trapezia* crabs, which prefer *Pocillopora* corals and often sport spots, *T. glaberrima* has a remarkably smooth, "clean" shell and a pair of unequal-sized pincers used for both delicate grooming and fierce defense.
### Habitat & Range This species is an Indo-Pacific specialist, ranging from the Red Sea and East Africa to the central Pacific islands. You won't find them wandering the reef floor; they are obligate symbionts of branching *Acropora* corals. They occupy the shallow, sun-drenched reef flats and crests where their host corals thrive, typically at depths of 1 to 15 meters.
### Behaviour Think of these crabs as the coral’s private security detail. They are fiercely territorial and usually live in mated pairs, defending a single coral colony against all rivals. To an observer, they may seem shy, scurrying into the deepest recesses of the coral when a shadow passes. However, if a predator like a Crown-of-Thorns starfish attempts to eat the coral, these tiny "guard dogs" become incredibly aggressive, rushing out to pinch the starfish’s sensitive tube feet until it retreats.
### Diet The crab’s diet is a masterclass in mutualism. They primarily feed on the nutrient-rich mucus secreted by the coral polyps, which they "comb" off using specialized hairs on their legs. They also consume detritus and settled organic matter, effectively acting as a living vacuum cleaner that prevents the coral from being smothered by sediment.
### Fascinating Fact The relationship is so sophisticated that the host coral actually produces specialized "fatty bodies"—lipid-rich tissue tips—specifically to feed the crabs. It is a rare example of a plant-like animal "farming" its own protectors by paying them in high-energy snacks!