Calcinus vachoni Forest, 1958

Poupin, J., Boyko, C. B. & Guzmán, G. L., 2003, Calcinus hermit crabs from Easter Island, with biogeographic considerations (Crustacea: Anomura: Diogenidae), Memoirs of Museum Victoria 60 (1), pp. 91-97 : 95

Calcinus vachoni Forest, 1958

Calcinus vachoni Forest, 1958: 285 , figs 2, 3, 9, 10, 15, 19 (type locality: near Nha Trang, Vietnam).— Baba, 1982: 58.— Morgan, 1990: 11, fig. 2; 1991: 905, figs 60–62.—Gherardi and McLaughlin, 1994: 624.— Poupin, 1997: 712, figs 6e–f, 8a–f.— Shih and Lee, 1997: 22, figs 1–3.— Shih, 1998: 93, figs 33–35.— Kato and Okuno, 2001: 74.

Calcinus seurati . — Matsuzawa, 1977: pl. 79, fig. 3.— Miyake, 1983: 113.— Nomura et al., 1988: 113.— Takeda, 1994: 194, fig. 2. Not Calcinus seurati Forest, 1951 .

Not Calcinus vachoni . — Lewinsohn, 1982: 53 (= Calcinus guamensis Wooster, 1984 , see Distribution).

Material examined (all specimens from Easter I.). Los Motus, in Pocillopora coral, 1 male 3.7 mm ( MZUC F1198 , 3257 ). Te Pito Kura, 1 male 1.2 mm ( AMNH 18198 ). Hanga Roa, discoloured specimens 1 male 1.6 mm, 1 female 1.7 mm ( MNHN Pg 6094) .

Diagnosis. Ocular acicle with 2–5 terminal spines. Anterolateral plate of branchiostegite with fringe of long setae on dorsal margin, unarmed. Outer face of left chela regularly convex, slightly granulate; lower margin of palm rounded; upper margin unarmed, rounded or weakly cornered. Right chela with 5–7 corneous spines on upper margin. Distal setation of P3 more pronounced than on distal P2 but not forming real brush of setae. Telson with 4–9 spines on left posterior lobe (3–5 on posterior margin and 1–4 on lateral margin) and 3–9 spines on right posterior lobe.

Colour (live coloration from Poupin, 1997). Ocular peduncle gray-blue to cream with a large dark patch of variable extension: from absent to almost covering all the peduncle. Antennular peduncle and its flagella, blue. Distal segment of antennal peduncle orange; flagellum orange. Cheliped almost totally gray-blue turning to white on fingers of chela. P2 and P3 uniformly cream. In Easter I. specimens examined herein coloration has almost totally faded.

Distribution. Widely distributed in Indo-West Pacific, 27°N – 27°S. Mauritius, Western Australia, Vietnam, Taiwan, Micronesia, Japan, French Polynesia, and Easter I.. According to Gherardi and McLaughlin (1994), the record from Somalia ( Lewinsohn, 1982) is in fact referable to Calcinus guamensis Wooster, 1984 .

Habitat. Hard bottom and facultative associate of Pocillopora corals. It uses gastropod shells of Drupa spp. , Drupella spp. , Conus spp. , Mitra spp. , Latirus spp. , Cymatium spp. , Coralliophila spp. , and Cronia spp. ( Shih and Lee, 1997: 25).

Remarks. Separation of the poorly preserved specimens herein reported of Calcinus vachoni from discoloured juveniles of C. imperialis , can be difficult. The characters that are most useful are: armament of ocular acicle and telson, aspect of left chela, and in the case of one specimen, faint traces of coloration (ocular peduncle, white with cream patch distally, and distal segment of antennular peduncle blue).

In armament of the ocular acicle and telson, general aspects of left and right chelae, and distal setation of P3, Calcinus vachoni is similar to Calcinus gouti Poupin, 1997 , from French Polynesia, and Calcinus laurentae Haig and McLaughlin, 1984 , from Hawaii. However, these three species are very distinctive in their coloration (see Poupin, 1997; Hoover, 1998). The ocular peduncle is gray-blue to cream with a large dark patch in C. vachoni ; orange with narrow white ring close to cornea in C. laurentae ; and proximally pink, grading to pale pink or white distally in C. gouti . The distal antennular segment is blue in C. vachoni ; light orange or white in C. laurentae ; and white to cream in C. gouti . The chela is gray-blue turning to white distally in C. vachoni ; brown turning to white distally in C. laurentae ; and white or cream with a submedian dark spot on outer face in C. gouti . P2 and P3 are uniformly cream in C. vachoni ; red-orange turning to pinkish distally in C. laurentae ; and cream with pink rings in C. gouti . In addition to coloration, Calcinus vachoni is also distinguished by the upper margin of the left chela, unarmed and often weakly cornered, whereas it has some spines and is rounded in the two other species.