Isocheles pilosus

Isocheles pilosus (Holmes, 1900)

(Fig. 40A–C, Pl. 8D)

Holopagurus pilosus Holmes, 1900: 154. — Schmitt 1921: 127, pl. 17, fig. 2. — Provenzano 1959: 377.

Isocheles pilosus. — Forest 1964: 294. — Haig et al. 1970: 17. — Haig & Wicksten 1975: 102. — Wicksten 1979c: 100; 1988b: 321. — Haig & Abbott 1980: 584, fig. 24.9. — Ricketts et al. 1985: 336, fig. 262. — Jensen 1995: 67, fig. 127. — Kuris et al. 2007: 648.

Diagnosis ( based on one specimen each from Newport Bay and Cabrillo Beach, Los Angeles County, California). Rostrum blunt, rounded, reaching about as far forward as lateral projections of carapace. Carapace bluntly triangular, as long as or slightly longer than wide. Second antennae setose. Eyestalks set close together, not dilated, exceeding antennal peduncle but not reaching distal end of antennular peduncle, cornea not dilated. Ocular acicle broad at base, extending into distal protion set at almost a 90˚ angle to basal area; distal portion with 3 strong clawlike spines, 3 strong setae. Antennae densely setose. Antennal acicle reaching close to 0.5 times length of eyestalk, set with small spines, setae. Chelipeds densely setose, similar in size, shape in smaller individuals but left chela wider in large adults. Carpus with with strong dorsal ridge bearing spines, 7–9 larger mesiolateral spines, two rows of larger dorsal spines, scattered rows of smaller spines along lateral margin. Hands horizontally flattened, set with prominent scattered spines, palms gently convex but with transverse depression anterior to base of fingers. Fingers with 3 or 4 rows of prominent spines, ending in sharp apices, without gape. Left cheliped widest across base of fingers, relatively narrower than larger, with inner, outer faces parallel. Pereopods 2, 3 with merus having tubercles, long setae, carpus with 2 rows of dorsal tubercles, mesial margin tuberculate, set with long setae; propodus with strong dorsal spinulose ridge, with rows of long, simple setae; dactyls long, gently curved, with lateral groove, flattened toward apex. Pereopod 4 ischium bearing two large ventral prominences, tuft of lateral setae; merus with lateral, dorsal tufts of elongate setae, carpus with tuberculate dorsal margin, dorsal, lateral tufts of elongate setae; propodus with lateral tuft of setae, well-developed granulate bean-shaped propodial rasp fringed dorsally by stiff setae; dactyl with 5 strong darkly pigmented teeth, fringe of elongate setae. Pereopod 5 chelate. Telson nearly as long as wide, slightly asymmetrical, left lobe slightly longer than right, lateral margins set with acute stiff setae, distal margin with 16 minute teeth, simple setae. Carapace length of larger examined specimen 7.8 mm.

Color in life. Carapace and antennae mottled with bluish, gray tints. Chelipeds cream to orange with bluish tinge on upper surface, line of brick red along chela. Pereopods 2, 3 tan to whitish, marked with brick red stripes. The color notes are from specimens from Cabrillo Beach, San Pedro, California.

Habitat and depth. Medium-grained sand of beaches, low intertidal zone to 55 m.

Range. Bodega Bay, California to Estero de Punta Banda, Baja California, Mexico. Type locality off San Diego, California.

Remarks. Holmes (1900) and Schmitt (1921) provided only a short diagnosis and poor illustrations of this species. Schmitt (1921) reported that the carapace length "of the single Bay specimen" was 28 mm. This length is far greater than that of any specimen I have examined.

This hermit crab can be very abundant on sandy beaches. It inhabits shells of Polinices spp., Callianax biplicata (G.B. Sowerby, 1825); Caesea fossatus (Gould, 1850); and other sand-dwelling gastropods. The crab can scurry on top of the sand or dig into the sand, leaving only the oral region, eyestalks and antennae exposed. It can feed in three ways: raking the surface of the sand with the third maxillipeds, capturing particles filtered by the antennae, or using the chelae to pick up food (Wicksten 1988b).

The southern range limit of this species is uncertain. Specimens identified as Isocheles pilosus have been collected at Ballenas Bay, Boca de San Domingo, Hughes Point and San Juanico Bay (Haig et al. 1970) and Magdalena Bay, Baja California (Wicksten 2006), but the identification is uncertain.

Provenzano (1959, as Holopagurus pilosus) mentioned that this species is very similar to the western Atlantic species Isocheles wurdemanni. Stimpson, 1860. He noted that I. wurdemanni had chelipeds that could have hands equal in size or the left larger than the right. In specimens that I have examined, these two species differ in three major features: I. pilosus is much more setose than I. wurdemanni; the dactyl of pereopod 4 bears teeth in I. pilosus and not in I. wurdemanni, and the telson bears numerous small teeth in I. pilosus but only as many as three on each side in I. wurdemanni. A fine illustration of I. wurdemanni by Provenzano (1959) is marred by an incorrect placement of the chelipeds relative to the eyestalks and antennae.