Carpilius maculatus
Spot the round-shelled 7-11 crab tucked under Hawaii's reef ledges, an uncommon find in warm 22-28C water year-round.
A rounded, smooth-shelled crab that looks almost polished, with a reddish-orange to brownish carapace scattered with black or dark spots that give it its name (count roughly seven to eleven spots, though the tally varies). It grows to about 13 cm across the shell, chunky and solid rather than flat, with thick claws tucked in close to the body. Usually seen wedged into a crevice or under a ledge rather than out in the open.
Divers usually find it by torchlight or by peering into a crack in the reef, sitting still and holding its ground rather than scuttling off. It is not a swimmer or an open-water forager, spending most of daylight hours tucked under coral heads and rubble ledges. Approach slowly and it will typically just sit tight rather than react.
Despite its solid, almost armoured look, this crab relies on its heavy claws to crush hard-shelled prey like snails and other crabs rather than on speed or camouflage to get by.
No clear seasonal pattern shows up in the sightings, and its comfortable range of roughly 22 to 28C matches Hawaii's reef water most of the year, so treat this as a year-round possibility rather than a seasonal target.
Logged sites are concentrated in Hawaii, United States, where it turns up wedged into reef crevices. It is not a species with a wide recorded spread elsewhere in the data, so Hawaii is currently the reliable place to look.
Mapping where 7-11 Crab is logged…
The strongest and most consistent sightings come from Hawaii, United States, where divers find it wedged into reef crevices and under ledges. It is logged as uncommon even there, so treat any encounter as a bonus rather than a guaranteed find.
There is no detected seasonal pattern for this species, and its preferred water temperature of roughly 22 to 28C is present in Hawaii year-round, so sightings are not tied to a particular month.
Look for a rounded, smooth reddish-orange shell dotted with black spots, roughly the size of your palm at up to 13 cm across. It sits tucked into reef crevices rather than moving in the open, with thick claws held close to the body.
They reach around 13 cm across the shell, making them a solid, chunky reef crab rather than a tiny cryptic species.
Its common name comes from the scatter of dark spots on its shell, which divers and collectors historically counted as falling somewhere between seven and eleven, though the exact number varies from crab to crab.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
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2,422 sites
