Fabia subquadrata Dana, 1851

Wicksten, Mary K., 2012, Decapod Crustacea of the Californian and Oregonian Zoogeographic Provinces 3371, Zootaxa 3371, pp. 1-307 : 247-248

Fabia subquadrata Dana, 1851

( Fig. 56M, N)

Fabia subquadrata Dana, 1851: 253 . — Holmes 1900: 87 (part). — Rathbun 1917: 102, pl. 24, figs. 1, 3; text fig. 53 (part) — Schmitt 1921: 253, pl. 39, figs. 1, 2; text fig. 150. — Johnson & Snook 1927: 391, fig. 347. — Davidson 1968: 85, fig. 1A. 1D, 1G, 1H. — Schmitt et al. 1973: 24. — Garth & Abbott 1980: 612, fig. 25.31. — Hart 1982: 226, fig. 93. — Ricketts et al. 1985: 221, fig. 179. — Campos 1986: 238. — Jensen 1995: 30, fig. 39. — Campos-Gonzalez 2007: 644, pl. 321 B3.

Raphonotus subquadratus . — Rathbun 1904: 186. — Weymouth 1910: 55, fig. 2.

Diagnosis. Carapace smooth, membranous, subquadrate; soft in adult female, hard in male. Female front sharply deflexed with transverse sulcus across vertical front between orbits. Anterolateral margin rounded, marked by round cluster of pits, male with dense pubescence along margin. Antennules in very wide grooves. Male with large orbits. Palp of third maxilliped about as long as adjacent segment, merus with small point on distomedial margin. Palm of chela widened distally, bearing 2 rows of setae along lower margin. Immovable finger with large serrate lobe on upper margin; dactyl with 1 large tooth on lower margin, upper margin with tuft of dense setae. Pereopods 2–5 with segments flattened, margins densely pubescent, dactyls large, subequal, curved. Male abdomen with terminal segment semi-circular, lateral margins of penultimate segment distally depressed, broader at proximal end than distal but not markedly so. Male carapace length to 7.3 mm, female to 16.2 mm.

Color in life. Translucent whitish to yellowish, at times with dark areas on carapace ( Jensen 1995).

Habitat and depth. Usually commensal in pelecypods, especially mussels, Mytilus spp. , and soft-shell clams, Mya arenaria Linnaeus, 1758 . Also reported from other pelecypods, rarely sea urchins, ascidians; intertidal zone to 220 m. Garth & Abbott (1980) gave a list of hosts.

Range. Akutan Pass, Aleutian Is. to Todos Santos Bay , Baja California, Mexico. Type locality Puget Sound .

Remarks. The grooved mussel crab perhaps is the largest and best known of the pinnotherids of the western coast of North America. Its change of size, shape and habitat during its life cycle can cause confusion with other species. Smaller individuals are more setose and can swim. The first host usually is a clam. The crabs produce hard shells prior to molting, accomplished while the crabs swarm into the plankton. Ovigerous females develop a large, soft exoskeleton later when they move to a larger host, often a mussel. Males remain hard-shelled. Garth & Abbott (1980) gave additional information and references on the life cycle.