Excerpts from Jim Conrad's
Naturalist Newsletter

Anemone Crab, MITHRACULUS CINCTIMANUS, top view

from the April 5, 2015 Newsletter issued from Río Lagartos, on the north-central coast of Yucatán, MÉXICO
ANEMONE CRAB

During an especially low tide, Rayo and I were out exploring in and around an exposed, decaying metal pipe left over from when they excavated and dredged the canal across the estuary from Río Lagartos. The top of the pipe has been torn away, leaving the bottom like a long bathtub holding water when the tide goes out. In and around this old pipe you can find organisms not encountered in the surrounding vast, flat, seagrass-populated shallows. During this particular visit, Rayo plucked a critter from inside the pipe we hadn't seen before. It's shown above.

This crab is so heavily encrusted with algae and calcium carbonate that its yellowish-red color and general form are hard to make out. In that picture the pointy head is at the bottom. A view of the crab's bottom, better displaying the smallish, slender, banded claws at the picture's bottom, is shown below:

Anemone Crab, MITHRACULUS CINCTIMANUS, bottom view

A close-up of what's encrusting the crab's surface, or exoskeleton, is shown below:

Anemone Crab, MITHRACULUS CINCTIMANUS, close-up of encrustation on body

The white, crusty stuff seems to be calcium carbonate. The slender items looking like moss plants bearing spore-producing capsules appear to be the crab's own hairs, providing good anchorage for algae, whose presence camouflage the crab's body.

This is the Anemone Crab, MITHRACULUS CINCTIMANUS, found from Florida south through the Gulf of Mexico and Caribbean to northern South America. Often Anemone Crabs live inside sea anemones, where they appear to be immune to the anemone's stings. Most pictures of living Anemone Crabs show the crab with its hind parts hidden among the anemone's tentacles, with only its front visible, peeping up through the tentacles.

Anemone Crabs don't prey on animals but rather eat algae, particles of organic matter, mucus associated with the anemone's ejected digested food, and other such material. They are omnivores whose modest claws are less adapted to snapping prey than to scraping at films of algae and mucous.