Security for Granular Claw Crabs

Security for granular claw crabs, Oedignathus inermis, is an abandoned barnacle shell. They have to locate protection because their soft-shelled abdomens are vulnerable and nutritious. The specific epithet, inermis, means unarmed. Some people call O. inermis soft-bellied crabs. They are much sought by predators.

Granular claw crab, Oedignathus inermis, in an empty giant barnacle shell

Seeing more than the pinching claw, which serves to block and camouflage the hideaway, is a rarity. But sometimes luck is on our side. I exposed the one belowby displacing a protecting veil of algae.

Oedignathus inermis, showing off it's oversize pinching claw. The whole crab exposed on a rock.
Oedignathus inermis, showing off its oversize pinching claw

The security of empty barnacle shells and other cover has its limits. Just after dawn, when the lowest tides permit, gulls go to work. On the exposed reefs you’ll see them checking barnacles shells, crevices, and small holes; you’ll even see them flipping algae. Discover the discreet niche that conceals the crab, and a tasty treat is yours.

Remains from the hunt – Oedignathus inermis pinching claw, abandoned on the reef


Harbo, R. M. 2011. Whelks to Whales: Coastal Marine Life of the Pacific Northwest. 2nd ed. Harbour Publishing Co.

Lamb, A. and B. P. Hanby. 2005. Marine Life of the Pacific Northwest. Harbour Publishing.

Kozloff, E. N. 1993. Seashore Life of the Northern Pacific Coast. 3rd ed. University of Washington Press.

Web Resources

Post on the granular claw crab in The Natural History of Bodega Head blog here.



  1. What beautiful colours the crab is, especially in the second picture. I was most surprised, when I looked at the crab I thought he was quite big, then read that he likes to live in barnacle shells!

    1. Up clase, those are some fantastic colors. To give you a sense of size, the barnacles they like to live in can get as big as a human fist; the crabs would fit in the palm of your hand. I didn’t write this, but they are almost always found in pairs. You can see a second crab in the photo you referred to.

  2. Gorgeous photos! Your blog is a wonderful reminder that another whole world exists within our own. As an ocean/beach lover, I appreciate the education you offer!

  3. Those crabs look scary but interesting. I would be gaping at the intracate potrusions on it’s body and then too late will it withdraw to safety. I hope something of me is left behind on the beach!

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