Soldier Porcelain Crab

Petrolisthes militaris is a ten-legged species from the Porcellanidae family.

Description

Pale red and covered with darker red spots; white bandson legs; claws and fore carapace appear to be composed of overlapping plates, reminiscent of medieval armor. Carapace slightly longer than broad; gastric region with conspicuous transverse ridges, protogastric ridges distinct; branchial margin moderately convex, with 4 or 5 spines on median portion, last spine largest. Branchial region with 2 epibranchial spines. Rostrum produced beyond eyes, relatively narrow, triangular; lateral lobes not produced; supraocular margin oblique, with distinct spine.

This porcelain crab is one of the most abundant crabs on tropical Australian reefs. They characteristically flattened body helps this crab to squeeze into tight spaces between bits of coral rubble and stones. Porcelain crabs are filter feeders and have large feathery mouthparts for collecting food from the water column. The large claws are therefore used defensively, but are more likely to be autotomised (fall off) to distract predators, much in the same way a lizards tail is.

Distribution

Indo-West Pacific, also Japan.

Habitat

Shallow water, at least 30 m. Found in reef habitats typically in rubble.

Morphology

Dorso-ventrally flattened body, claws with distinct sculpturing and often a fringe of 'hair' along anterior margin.

Evolution

The porcelain crabs are not true crabs, but are the result of an independent but convergent evolutionary lineage more closely related to hermit crabs.

Behaviour

Porcelain crabs are shy creatures, and will very quickly retreat from threats. They can use their abdomens to swim backwards by rapidly flicking it, much like a shrimnp would.