Scyra acutifrons Dana, 1851

Wicksten, Mary K., 2012, Decapod Crustacea of the Californian and Oregonian Zoogeographic Provinces 3371, Zootaxa 3371, pp. 1-307 : 224-226

Scyra acutifrons Dana, 1851

( Fig. 52D, E; Pl. 13A)

Scyra acutirons Dana, 1851: 269 . — Holmes 1900: 41. — Rathbun 1904: 175; 1925: 195, pl. 79; pl. 224, figs. 4 5; text fig. 79. — Weymouth 1910: 33, pl. 6, fig. 17. — Schmitt 1921: 214, text figs. 134a, b. — Johnson & Snook 1927: 374, fig. 329. — Garth 1958: 252, pl. P, fig. 1; pl. 27, fig. 1. — Garth & Abbott 1980: 600, fig. 25.9. — Hart 1982: 190, fig. 76. — Ricketts et al. 1985: 169. — Jensen 1995: 21, fig. 13. — Hendrickx 1999: 156, fig. 90, pl. 6D, E. — Kuris et al. 2007: 641.

Diagnosis. Rostrum flattened, short, horns shaped like feathers or arrow; rows hooked setae on horns. Carapace pyriform; median region separated from cardiac, branchial regions by conspicuous depression; acute tubercle near center of median region, larger tubercle behind it. Branchial region with felt-like setae, bearing large, projecting tubercle; elevated prominence proximal to tubercle, usually bearing several small tubercles; large tubercle on cardiac region, smaller tubercle on intestinal region. Considerable variation among individuals, between sexes in width of carapace, degree of prominence, elevation of tubercles and regions of carapace. Preorbital spine acute. Pterygostomian regions with several rounded teeth. Two spines on outer margin of basal antennal segment, lobe on its outer margin, flagellum long. Male cheliped considerably more robust than those of female, merus subcylindrical, somewhat flattened below, bearing pustules; carpus pustulate, ridges on outer side; hand long, narrow, compressed, palm often with inflated ridge; fingers deflexed, in older male, gaping, with tooth near base of dactyl. Pereopods 2–5 subcylindrical, pubescent, propodi bearing groove on either side; dactyls short, rounded at apex. Male carapace length 46.5 mm, width 33.7 mm; female 23.9 mm, width 15.9 mm.

Color in life. Dull tan to gray with red marks on chelipeds, walking legs.

Habitat and depth. Rocks, rocky reefs, pilings; intertidal zone to 114 m but usually less than 50 m. As noted by Kuris et al. (2007), the species is rare in the intertidal zone.

Range. Kachemak Bay , Cook Inlet, Alaska to Point San Carlos, Baja California. Type locality " Oregon.”

Remarks. Scyra acutifrons usually does not decorate, but instead is encrusted by sponges, barnacles, bryozoans or tunicates. Garth & Abbott (1980) reported that they rest with the anterior region aimed downward, but I have not observed any consistent posture in these crabs.

Garth (1958) noticed that there were two distinct types of this crab. The "northern form" has a raised carapace with the gastric region deeply separated from the cardiac and branchial regions, and a broad rostrum. The "southern form" has a more rounded carapace and a narrow rostrum.

It is easy to confuse this species with similar subtidal spider crabs. Juvenile Loxorhynchus spp. are much more setose than S. acutifrons , decorate themselves, and possess a down-curved rostrum. The rostrum of Oregonia gracilis is much more elongate than that of S. acutifrons .

Ricketts et al. (1985) claimed that S. acutifrons was "uncommon below Pacific Grove", but this is not so. The crab is common on subtidal rocks and jetties along the mainland coast of Los Angeles County, California, but rarely is found on the islands of southern California.