Calcinus imperialis Whitelegge, 1901

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 : 94

Calcinus imperialis Whitelegge, 1901

Calcinus imperialis Whitelegge, 1901: 48 , pl. 9 (type locality: Lord Howe I.).— Grant and McCulloch, 1907: 154.— Chilton, 1911: 552.— DiSalvo et al., 1988: 458.— Morgan, 1991: 882, figs 21–23.— Tudge, 1995: 11, pl. 1, fig. 1f. — Poupin, 1997: 697, figs 3f', 5c, 7d.—Forest et al., 2000: 15.— Forest and McLaughlin, 2000: 79.

Not Calcinus imperialis .— Wooster, 1984: 130.— Poupin, 1996: 14 (= Calcinus isabellae Poupin, 1997 ).

Material examined (all from Easter I.). Hanga Poukura, 1 female 1.8 mm ( AMNH 18185 ) . Hanga Tee, 1 male 1.5 mm ( AMNH 18186 ) . Easter I., 2 males 1.9–2.0 mm ( AMNH 18187 ) , 3 females 1.7–2.9 mm, discoloured specimens 1 male 1.9 mm, 1 female 1.6 mm ( AMNH 18188 ) . Easter I., 1 female 2.7 mm ( AMNH 18189 ) . Tongariki, 1 female 2.1 mm ( AMNH 18190 ) . Hanga Tee O Vaihu, discoloured specimens 2 males 1.3–1.7 mm ( AMNH 18191 ) . Hanga Tee O Vaihu, 6 males 1.4–3.4 mm, 4 females 1.4–2.2 mm, 1 juvenile 1.3 mm, discoloured specimens 6 juveniles 0.9–1.4 mm ( AMNH 18192 ) . La Pérouse Bay, 2 males 1.9–3.8 mm, discoloured specimens 2 males 1.1–1.4 mm, 1 female 1.0 mm, 5 juveniles 0.9–1.0 mm ( AMNH 18193 ) . Te Pito Kura, 3 males 2.3–2.9 mm, 1 female 1.8 mm, discoloured specimens 7 males 1.0– 1.7 mm, 4 females 1.2–1.5 mm ( AMNH 18194 ) . Anakena, 2 males 1.6–3.5 mm, 2 females 1.6–2.2 mm ( AMNH 18195 ) . Anakena, 2 males 1.9–3.5 mm, 2 females 1.6–3.3 mm, discoloured specimen 1 female 1.3 mm ( AMNH 18196 ) . One Makihi, 1 male 4.4 mm ( AMNH 18197 ) . Hanga Roa, 2 males 2.8–4.4 mm, discoloured specimens 9 males 1.3–1.9 mm, 3 females 1.6–2.1 mm ( MNHN Pg 6093) .

Diagnosis. Ocular acicle with a single terminal spine. Ocular peduncle 0.7–1.0 times as long as shield; diameter of cornea included approximately 5 times in peduncular length. Anterolateral plate of branchiostegite with fringe of long setae on its dorsal margin (no spinules). Left chela 0.8–1.3 times as long as shield, comparatively larger in adult males. Outer face of palm feebly granular, with several proximal tubercles; lower half with 2 or 3 circular or subcircular depressions; upper margin armed with 3–5 spiny tubercles; lower margin denticulated and carinate, carena continuing onto fixed finger (see remarks). Carpus armed with several stout spines along anterior and upper margins and on outer face. Right palm with 4 or 5 corneous-tipped spines on upper margin; outer face tuberculate. P3 with distinct brush of setae on ventral margin of dactyl and distal part of propodus; dactyl about 0.8 times as long as propodus. Telson armed with single spine on terminal margin of each posterior lobe.

Colour. (live coloration from Poupin, 1997). Shield and ocular peduncles green olive. Antennular and antennal peduncles yellow. Chelae green olive with purplish-blue spines and tubercles, tip of fingers white. Dactyls of chelae with 2 red spots near base, on inside and outside. P2 and P3 banded in light yellow, black, and green olive. Abdomen and telson white.

After 1.5 y in alcohol, coloration still clear on Easter I. specimens although slightly different from live coloration. Shield white, sometimes cream on distal half. Antennular and antennal peduncles chlorine yellow. Palms of chelae orange to brown, fading to white distally; tubercles and spines blue. Dactyls of chelae with 2 red spots near base, on inside and outside. P2 and P3 banded in white, red-brown, and orange.

Distribution. South Pacific 14– 34° S. Eastern Australia to Easter I., including Vanuatu, New Caledonia, Norfolk I., Kermadec Is, and French Polynesia. Not found in the Indian Ocean or in North Pacific, and the report from these areas by Forest and McLaughlin (2000: 79) is erroneous (J. Forest, pers. comm.).

Habitat. This species is a non-obligate coral associate (genus Pocillopora ). On Easter I. it uses gastropod shells of Caducifer decapitata englerti , Erosaria caputdraconis , Fossarus cumingii , Neothais nesiotes , Nerita sp. , Planaxis akuana, Pascula citrica, and Nodilittorina pyramidalis pascua . Two specimens ( AMNH 18187) were parasitised by the bopyrid isopod, Pseudionella akuaku Boyko and Williams, 2001 .

Remarks. The occurrence of Calcinus imperialis in Easter I., although already mentioned by DiSalvo et al. (1988), had been overlooked in the taxonomic literature. These new collections are the second record of this species on Easter I. and show that it is very common around the island.

Examination of Calcinus imperialis specimens herein reported, reveals intraspecific variations. Unusual armament of the ocular acicle includes one additional small spine, on one or both sides (13 specimens out of 79) or up to three terminal spines, on one side (a single specimen). The distal brush of setae on P3 is somewhat weak on a few small specimens. The two or three circular or subcircular depressions on the outer face of the chela are attenuated, or even totally absent, on specimens smaller than 2.0 mm. The outer face of the palm is either regularly convex or only slightly concave on its lower half. In these cases identification can still be made by careful examination of the lower margins of the palm and fixed finger, which are almost always carinated. In combination with the armament of the ocular acicle and telson, this character was very useful in identifying many juveniles lacking colour. The carina was missing only on a 1.6 mm female ( AMNH 18188) although it was easily identified as C. imperialis by the faint remains of red spots at the bases of the dactyls of the chelae.