Spotted Porcelain Crab: Neopetrolisthes maculatus

The spotted porcelain crab is commensal on sea anemones, meaning that the crab benefits from the anemone (protected by the stinging tentacles) while the anemone is neither helped nor harmed by the presence of the crab.

Unlike true crabs, porcelain crabs (family Porcellanidae) have long antennae, a greatly-reduced fourth pair of legs which remain hidden beneath the carapace, and feed by filtering planktonic nutrients from the water with fanlike mouth parts called setae.  (Ref: Humann & DeLoach 2010).

In this video you can see the elaborate filter-feeding setae in action.  Spot patterns range from fine red spots to large polygonal red spots on a white background.  Spotted porcelain crabs are found throughout the Indo-Pacific and Japan.  These video clips were filmed in the Philippines, and I have only very rarely seen them in Guam.