Family PORCELLANIDAE Haworth, 1825

<em>Lissoporcellana quadrilobata </em>[from Miers 1884: pl. 30 fig. D]

Lissoporcellana quadrilobata [from Miers 1884: pl. 30 fig. D]

<em>Petrolisthes haswelli</em> [from Miers 1884: pl. 29 fig. A]

Petrolisthes haswelli [from Miers 1884: pl. 29 fig. A]

<em>Polyonyx obesulus</em> [from Miers 1884: pl. 29 fig. D]

Polyonyx obesulus [from Miers 1884: pl. 29 fig. D]

<em>Pachyeles sculptus</em> [from Grant & McCulloch 1906: pl. 2 fig. 2]

Pachyeles sculptus [from Grant & McCulloch 1906: pl. 2 fig. 2]

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Family PORCELLANIDAE Haworth, 1825

Porcellanidae Haworth, A.H. 1825. A new binary arrangement of the macrurus Crustacea. Philosophical Magazine and Journal 65: 183-184.

Introduction

Porcellanids are commonly known as 'Porcellain Crabs'. Unlike other anomurans they have the abdomen flattened and tucked under the body in a manner similar to true crabs; this crab-like impression is further enhanced by robust claws held out in front of the body. However, unlike true crabs, porcellanids have retained a well-developed tailfan.

Porcellanids occur in a wide variety of habitats across the continental shelf, but are most abundant in sheltered intertidal and shallow subtidal zones of reefs, rocky shores, and estuarine mangroves. Many have flattened bodies which allow them to live in narrow spaces on the undersides of rocks and dead coral; if the rocks are turned up the crabs are very quick to scurry out of sight. Others tend to be thicker-bodied, and are common members of epifaunal fouling communities. Commensal or ectosymbiont relationships are common in this family, with species frequently living in association with sponges, and on a variety of cnidarians such as Pennatulacea (sea pens), hard and soft corals, gorgonians and alcyonarians. The beautiful Neopetrolisthes maculatus lives commensally amongst the tentacles of giant anemones such as Stichodactyla, Entacmaea and Heteractis species. Another native Australian species, Polyonyx transversus (Haswell, 1882), is notable for living commensally inside the parchment tube of a large polychaete worm (Chaetopterus) and inside the shell cavity of bivalve molluscs (Aspergillum). Porcellanids are typically suspension feeders, catching food on long feathered setae as their elongate third maxillipeds are pulled through the water.

The Australian fauna is relatively diverse and includes 48 species in 13 genera. Even so, there has been relatively little taxonomic study, and the fauna is significantly more diverse than these figures indicate. The majority of modern work on this family has been undertaken by Haig (1964, 1965, 1966, 1973, 1974, 1978, 1979, 1981, 1987, 1988), Ball & Haig (1972) and Haig & Ball (1988)—all important papers for identifying the Australian fauna.

Diagnosis

Body more or less depressed and crab-like, carapace broadly ovate; frontal margin often forming broad triangular rostrum, but may be bilobate, trilobate or quadrilobate. Antennules concealed; antennal peduncles directed backwards. Third maxillipeds with ischium broad. First pereiopods chelate, broad, flattened or inflated; often held more or less horizontally or obliquely. Second to third pereiopods used as walking legs. Fifth pereiopods markedly reduced, thin, folded into more dorsal position, and resting in branchial chamber. Abdomen symmetrical, broad, and strongly flattened, folded under body, but not closing a sterno-abdominal cavity; first one or two segments visible dorsally; broad tailfan of telson and uropods well developed; telson divided into five or seven plates; female with two pairs of slender uniramous pleopods on fourth and fifth abdominal segments, often with additional pair on third; male with single pair of pleopods on second segment.