Loxorhynchus crispatus
Spot this decorator crab draped in sponge and algae on California reefs, uncommon but a rewarding find year-round in 12 to 19C water.
Roughly 6cm across, with a triangular, spiny shell almost entirely hidden under a self-applied covering of sponge, algae, and other debris it picks and attaches by hand. Look for the shape rather than the colour, since colour varies with whatever material it has stuck on that week. Long, thin walking legs poke out from under the disguise, giving away what would otherwise pass as a lump of rubble.
Sits motionless on rock or reef structure, relying entirely on its decorated shell to disappear into the background rather than fleeing when a diver approaches. Divers typically find it by scanning slowly for an oddly textured lump rather than by spotting movement. It's a benthic species, so check ledges, crevices, and rubble patches rather than open water.
It actively grooms and attaches sponge, algae, and other bits of the reef onto hooked bristles on its shell, rebuilding the disguise as it grows and moults, so no two individuals wear quite the same outfit.
Sightings show no detected seasonal pattern, and the observed temperature range of 12.3 to 18.8C spans California's water temperature swing across the year, so it's a reasonable year-round find rather than a seasonal special.
Reef neighbours a diver could mistake it for. Use the identification notes above to tell them apart.
Every logged sighting comes from California, United States, making it the place to look for this species. It turns up on rocky reef and kelp-adjacent benthic habitat along the California coast, mostly logged as uncommon with a couple of sites reporting it more reliably.
Mapping where Masking Crab is logged…
The species is most reliably logged in California, United States, on rocky reef habitat. All recorded sightings so far come from Californian dive sites.
There's no clear seasonal pattern in sightings, and its observed temperature range of 12.3 to 18.8C covers California's water year-round, so it can be found in any month.
Look for a small, roughly 6cm crab whose triangular shell is covered in sponge, algae, or debris rather than for any fixed colour pattern. The giveaway is the shape and the thin legs sticking out from under an otherwise camouflaged, motionless body.
They reach about 6cm across the shell, making them a small, easy-to-overlook find that rewards a slow, close look at rock and reef surfaces.
They decorate themselves by hand, attaching sponge, algae, and other reef material to hooked bristles on their shell, then rebuild the disguise every time they moult.
No. They are harmless, slow-moving, and rely on camouflage rather than defence, posing no risk to divers who come across them.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
Sally Lightfoot Crab
2,422 sites
