Four-Lobed Swimming Crab

Thalamita sima

The Four-lobed Swimming Crab, a member of the family Portunidae, is a small crustacean reaching up to 5.6 cm in carapace width. It is associated with reef environments and can be found in the Indo-Pacific region, including the Red Sea, East Africa, Japan, New Zealand, and Hawaii. This crab inhabits intertidal and subtidal zones, preferring sandy or muddy-sandy substrates. It is typically found at depths ranging from 0 to 50 meters, with most occurrences shallower than 40 meters. An omnivorous species, the Four-lobed Swimming Crab feeds on a variety of food items, including small invertebrates and organic matter. It is known to capture post-larval stages of other crustaceans, such as the American lobster. The species exhibits gonochoric reproduction, with a common precopulatory courtship ritual that involves olfactory and tactile cues, followed by indirect sperm transfer. Divers encountering this crab may find it in sandy-bottom habitats, often blending in with its surroundings. While not evaluated for conservation status by the IUCN, it is an interesting species to observe due to its ecological role and reproductive behaviors.