Calcinus aff. sirius Morgan, 1991

Poupin, Joseph & Lemaitre, Rafael, 2003, Hermit crabs of the genus Calcinus Dana, 1851 (Decapoda: Anomura: Diogenidae) from the Austral Islands, French Polynesia, with description of a new species, Zootaxa 391, pp. 1-20 : 17-18

Calcinus aff. sirius Morgan, 1991 ( Figs. 1 d, 4, 5b)

Material examined. French Polynesia, Austral Islands, BENTHAUS Expedition. Rapa, stn DW 1894, 27°40.13’S, 144°21.51’W, 100 m, 8.xi.2002: 1 ov. Ψ 5.5 mm ( MNHN Pg 6395).

Diagnosis. Ocular acicles terminating in simple spine. Left chela ( Fig. 5 b) with outer face regularly convex; upper margin of palm with 7 blunt spines; lower margin with few tubercles on distal half. Upper margin of right chela with 6 corneous­tipped spines. Dactyl of P2 ( Fig. 4 a, b) with 10 movable spines on ventral margin. Dactyl of P3 ( Fig. 4 c) slightly shorter than propodus, with 7 mobile spines on ventral margin. Ventrodistal pilosity of P3 weak, not much different from that of P2 ( Fig. 4 b, c). Telson with posterior lobes each armed with single terminal spine. Shield and posterior carapace orange ( Fig. 1 d). Ocular peduncles pale orange on proximal third, fading gradually to white on distal two­thirds. Antennular peduncles orange, becoming pale on distal fourth of terminal segment. Antennal peduncles orange, with white­tipped spines. Chelipeds bright orange. Ambulatory legs orange, with minute dark orange spots on setal pores. Abdomen red­brown; eggs red.

Habitat. The single specimen was found on coral bottom, at 100 m.

Remarks. Morgan's (1991) Calcinus sirius is known from eastern Australia ( Norfolk and Lord Howe Islands, Middleton and Elizabeth reefs, at 2–22 m), at a latitude similar to that of Rapa where the specimen of C. aff. sirius was collected. Should the specimen reported here be confirmed in the future to be C. sirius , it would represent a considerable range extension for this species.

In the specimen of C. aff. sirius from Rapa, the ocular acicles, telson, left and right chelae, and ventral armature of the dactyl of P2, are similar to those of C. sirius . However, the ventrodistal pilosity of P3 is similar to that of P 2 in the Rapa specimen, whereas pilosity is slightly more pronounced on P3 than on P 2 in C. sirius . Based on a single specimen it is not possible to determine the extent of variation that might exist in the ventrodistal pilosity of P3 and P2, a character known to vary intraspecifically in at least some Calcinus species (see Poupin & McLaughlin 1998: 22). The bright orange coloration of the specimen of C. aff. sirius also seems to differ from that of C. sirius , which at least in preserved specimens has been described as brown or dark brown, with cream on fingers and palm of chelae (Morgan 1991). Until ventrodistal pilosity of P2 and P3, and coloration can be fully evaluated in additional specimens from French Polynesia, and coloration of live C. sirius is documented, it is best to refer our specimen to C. aff. sirius .

Morphologically, the specimen of Calcinus aff. sirius bears some superficial resemblance to C. albengai , collected at the same station. However, it clearly differs from C. albengai in coloration ( Fig. 1 a, d), shape of left chela ( Fig. 5 a, b), and number of spines on the ventral margin of the dactyl of P2 (10 in C. aff. sirius , 6–8 in C. albengai ).

Figures

FIGURE 1. Live coloration (except b, taken several weeks after preservation): a, Calcinus albengai n. sp., deep­water variant, holotype ɗ 3.8 mm, Marotiri Isles, 100 – 120 m (MNHN Pg 6359); b, Calcinus albengai n. sp., shallow­water variant, ɗ 3.5 mm, Rapa Island, 53 m (MNHN Pg 6382); c, Calcinus gouti Poupin, 1997, ɗ 5.0 mm, Tikehau, 15 m (UF 1349); d, Calcinus aff. sirius Morgan, 1991, 1 ov. Ψ 5.5 mm, Rapa Island, 100 m (MNHN Pg 6395). Photographs by L. Albenga (a, b), G. Paulay (c), and J. Poupin (d).

FIGURE 4. Calcinus aff. sirius Morgan, 1991, ov. Ψ 5.5 mm, Rapa Island, 100 m (MNHN Pg 6395): a, distal part of propodus, and dactyl of left P 2, outer face; b, left P 2, outer face; c, left P 3, outer face. Scale bars 1 mm.

FIGURE 5. Left chela: a, Calcinus albengai n. sp., holotype ɗ 3.8 mm, Marotiri Isles, 100 – 120 m (MNHN Pg 6359); b, Calcinus aff. sirius, ov. Ψ 5.5 mm, Rapa Island, 100 m (MNHN Pg 6395). Scale bars 1 mm.