The Red-spotted Guard Crab, Trapezia tigrina, is a small, flattened crab with a trapezoidal carapace, typically reaching up to 25 mm (1 inch) in carapace width. Its smooth, pale yellow to cream-coloured carapace and robust chelipeds are marked with distinct reddish-brown to dark red spots. These spots are typically circular or oval, contrasting sharply with the lighter background. The specific epithet tigrina is Latin for "tiger-like," referring to this spotted pattern.
This species inhabits shallow coral reef ecosystems, typically found within the branches of Acropora corals at depths from 1 to 20 m (3-65 ft). It forms an obligate symbiotic relationship with its coral host, often living in male-female pairs. The crab cleans the coral surface of accumulating sediment and deters coral predators, notably the crown-of-thorns starfish (Acanthaster planci), by nipping at their tube feet. In return, the coral provides shelter and a food source consisting of coral mucus and undigested particles. Trapezia tigrina is territorial, using its strong claws to defend its host coral against intruders. Its diet primarily consists of coral mucus, plankton, and small invertebrates.
Female Trapezia tigrina carry fertilized eggs within a specialized brood pouch until they hatch as free-swimming larvae. These larvae undergo several planktonic developmental stages before settling onto the reef. Upon settlement, they metamorphose into juvenile crabs that then seek out suitable coral hosts to mature into adults.
- circular or oval spots
- robust chelipeds
