Opisthopus transversus Rathbun, 1893

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

Opisthopus transversus Rathbun, 1893

( Fig. 57A, Pl. 15B)

Opisthopus transversus Rathbun, 1893: 252 ; 1904: 188, text fig. 95; 1917: 173, pl. 37, figs. 4, 5; text fig. 110. — Holmes 1900: 97. — Weymouth 1910: 61, text fig. 9. — Schmitt 1921: 268, pl. 44, figs. 4, 5, text fig. 158. — Johnson & Snook 1927: 394, fig. 350. — Schmitt et al. 1973: 131. — Garth & Abbott 1980: 618, fig. 25.42. — Ricketts et al. 1985: 105, fig. 80. — Campos-Gonzalez et al. 1992: 754. — Jensen 1995: 31,fig. 44.— Campos-Gonzalez & Manning 2000: 799. — Campos-Gonzalez 2007: 644, fig. 321 C1.

Pinnotheres nudus Holmes 1895: 563 , figs. 1–5. — Rathbun 1917: 83, fig. 40. — Schmitt 1921: 252, fig. 149. — Johnson & Snook 1927: 391. — Schmitt et al. 1973: 60.

Not Pinnotheres nudus Weymouth, 1910: 53 , fig. 1; = Zaops geddesi ( Miers, 1880) ; Atlantic species; see Campos & Manning 2000: 803.

Diagnosis. Carapace somewhat rounded, convex, moderately hard. Front deflexed, almost straight, with slight median groove. Antennules well developed, set in deep notches. Third maxilliped with ischium well developed, merus broad, palp 3-jointed, last joint articulated on inner side of preceding joint. Chelae short, stout. Pereopods 2–5 similar to each other, segments rather broad, dactyls curved, small. Abdomen of male narrow at base, tapering from third segment to end; abdomen of female wide, long. Male carapace length to 10 mm, female to 17 mm.

Color in life. Carapace mottled with vermilion to deep red, legs banded with red to purple, background white to cream. The color notes are from crabs from Cabrillo Beach, Los Angeles County, California.

Habitat and depth. Commensal in mantle cavities of pelecypods, gastropods (including large opisthobranchs), and giant chiton Cryptochiton stelleri (von Middendorff, 1847) ; in cloacae of sea cucumbers, and with polychaete Chaetopterus variopedatus ; intertidal to subtidal zones.

Range. Monterey, California to San Ignacio Lagoon, Baja California ; San Felipe, Baja California ( Gulf of California) . Type locality Monterey .

Remarks. Evidence suggests that the color of the crab is dependent on the habitat and host. Crabs that inhabit suspension-feeding pelecypods tend to have less color than those that live in deposit-feeding or grazing hosts. Garth & Abbott (1980) gave further information and references.

After storms, the mottled pea crab may be cast ashore alive and away from a host. The crabs can crawl easily. It is not known if they move from host to host under normal conditions.