Knobs and bumps are not unknown among crabs, but a crab that is among the world’s bumpiest thrives on Orange County shores.

It’s called, appropriately enough, the lumpy crab, and sometimes the rubble crab. Both common names get the point across: a shell so burdened with bumps it looks a bit like a pile of gravel.

That might be the point. This red-brown crab is often found under rocks, where it remains immobilized, often in small holes, unless poked and prodded. The bumps are likely a bit of evolutionary camouflage to protect the crab from predators.

The crab also can be recognized by the darkened tips of its pinching claws.

At little more than an inch wide, the crab has plenty of predators to worry about. Black croaker, cabezon and scorpionfish are among the fish that would view the lumpy crab as a tasty morsel – that is, if they catch sight of it.

The crab itself attacks mainly algae.

Look for the crab in the surf zone (turning over rocks is not recommended, however, because of ecological disturbance it causes) or perhaps washed up onshore clinging to “holdfasts” – attachment points – on strands of kelp.

Once in a while the crabs might be seen trundling across the face of a rock; they also make appearances in tidepools – nature’s fishbowls, the depressions on rocky shores that retain water when the tide has receded.

Sharp eyes are needed; the crab’s camouflage works on humans as well as fish.

The crabs can also be found at the Ocean Institute in Dana Point, where they hide underneath anything they can find, according to the aquarist there.

The crab’s habits, she said, are similar to those of the retiring southerner crab, another oddity that has appeared in this column before.

Scientific name: Paraxanthias taylori

Sources: Aquarist Julianne Steers, Ocean Institute, Dana Point; “Seashore Life of Southern California,” By Sam Hinton.

Next week: Red-breasted merganser

Photo illustration by: Scott Brown

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