Rides the stalk of a sea pen and combs plankton out of the water with feathered mouthparts.
A small porcelain crab with a carapace under 2 cm, translucent white to pale pink and marked with fine red-brown lines, the claws slender and elongate and carried out in front rather than folded. Like all porcelain crabs it shows only three obvious pairs of walking legs, the fourth being reduced and tucked away, and it drops a limb readily when handled. Sea pens in this region carry two similar species, Porcellanella triloba and Porcellanella picta, separated on the shape of the front margin of the carapace and on the pattern of lines; they are not always distinguishable in a photograph. The anemone and crinoid porcelain crabs are heavier animals with much broader claws, and neither is found on a sea pen.
Lives on the stalk and rachis of sea pens standing in open sand and silt, usually a pair to a colony and often low down near the sediment where the stalk enters the bottom. It feeds by unfurling a pair of feathery third maxillipeds and sweeping them through the water to strain out plankton, the same method used by the porcelain crabs of anemones and crinoids. Recorded from about 5 to 30 m. Since sea pens generally stay contracted in the sediment during the day and expand after dark, the crab is mostly a night-dive animal, and when the host is touched the colony deflates into the sand and takes the crab down with it, which is the usual end of an encounter.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.
