Hairy hermit crab (Pagurus hirsutiusculus)
Hermit crabs are a common site on the intertidal zone of a rocky or sandy mud beach. Unlike most crabs, which have a full suit of armor to protect them from predators, hermit crabs have adopted another strategy: They protect their soft abdomens with the shell of a snail.
As they grow, they must spend lots of time looking for a bigger house to live in. When they come upon an empty shell, they will explore the inside to see if it fits and is of good quality. If it works, they slip out of the old and into the new, quick as a wink. Their soft abdomens are curved to fit in a snail shell, and one of their last pairs of legs are modified into hooks to hold the crab in the shell.
Of the several species of hermit crabs in our area, the hairy hermit is unique, with its multiple fine body projections that look like hairs. This specimen collects fine mud particles on the hairs, which probably serve to camouflage it on a mud or sand beach. Another distinguishing feature of this species is the banded antennae.
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This species and several other species occur along the West Coast from Alaska to Mexico. They range from the mid-intertidal zone to the shallow subtidal zone, where they feed on fine organic particles in the mud or other scraps that come their way.
Like other crabs, the females incubate the eggs by holding them on the abdomen with modified legs. After that, hatching larvae stay in the plankton until they mature and settle to the bottom.
David W. Jamison is a Boston Harbor resident and marine biologist.