Calcinus pascuensis Haig, 1974

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 : 92-94

publication ID	https://doi.org/ 10.24199/j.mmv.2003.60.13
persistent identifier	https://treatment.plazi.org/id/03AD87E6-E567-FFB3-6FB3-FDC2FD49FC62
treatment provided by	Felipe
scientific name	Calcinus pascuensis Haig, 1974
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Calcinus pascuensis Haig, 1974 View in CoL

Figure 1 View Figure 1

Calcinus pascuensis Haig, 1974: 27 View in CoL , figs 1–6 (type locality: Easter I.).— Retamal, 1981: 19.— DiSalvo et al., 1988: 458.— Poupin and McLaughlin, 1998: 24.

Material examined. Neotype (herein selected). Easter I., off Hanga Otea, 26 Aug 1999, 21 m, D. Hubbard, 1 male 5.3 mm ( AMNH 18177 View Materials ).

Other specimens (all from Easter I.). Off Ana O Keke, Poike, 1 male 4.0 mm ( AMNH 18178 View Materials ) , 1 female 3.9 mm ( MNHN Pg 5948) . Oroi Point , 1 female 1.5 mm ( AMNH 18179 View Materials ) . Hanga Tee O Vaihu , 1 male 1.8 mm ( AMNH 18180 View Materials ) . La Pérouse Bay, 2 males 1.9–2.1 mm, 1 female 1.7 mm ( AMNH 18181 View Materials ) . Piko , 3 males 1.7–2.0 mm, 2 females 1.3–1.7 mm ( AMNH 18182 View Materials ) . Te Pito Kura , 1 male 3.0 mm, 3 females 1.4–2.2 mm ( AMNH 18183 View Materials ) . Piko , 1 male 3.6 mm ( AMNH 18184 View Materials ) . Hanga Roa , 1 male 2.6 mm, 1 female 2.4 mm ( MNHN Pg 6092) .

Diagnosis. Ocular acicle with a single terminal spine. Chelipeds, P2 and P3 with long and distally plumose setae, typically with club-like aspect. Outer face of left palm regularly convex. Upper margin of right palm with 4 or 5 strong corneous-tipped spines. Dactyls of P2 and P3 equal to or slightly shorter than propodi; distal degree of setation similar for both pereopods, without distal brush of setae on P3. Telson with 2–16 (usually 10) spines on lateral and posterior margins of left posterior lobe, and 2–7 (usually 6) spines on right posterior lobe.

Redescription. Shield 0.8 as broad as long; anterior margin between rostrum and lateral projections slightly concave; anterolateral margin setose; anterolateral plate of branchiostegite armed by row of spinules on dorsal margin. Rostrum broad, obtusely triangular, largely exceeding small lateral projections. Ocular acicle subtriangular, terminated by single acute spine. Ocular peduncle 0.8–1.0 as long as shield, left slightly longer than right; diameter of cornea included 5–7 times in peduncular length ( Fig. 1a View Figure 1 ).

Antennular peduncle extending to distal 0.25 of ocular peduncle; basal segment usually with 3 spinules at ventrolateral distal angle; penultimate segment unarmed; ultimate segment unarmed, equal to 0.33 of shield length. Antennal peduncle reaching to distal 0.33 of ocular peduncle, furnished with long and distally plumose setae. First segment minutely spinose at ventrolateral distal angle. Second segment with dorsolateral distal angle produced, terminating in strong bifid spine; dorsomesial surface inflated, produced as strong spine. Third segment with ventrodistal spine. Fourth segment with distodorsal spine. Fifth segment long and unarmed. Antennal flagellum overreaching distal end of P2. Antennal acicle surpassing distal end of penultimate segment of antennal peduncle, produced as strong spine, upwardly curved; dorsolateral margin with 2 spines; dorsomesial margin with 2–3 spines.

Left cheliped larger than right ( Fig. 1b View Figure 1 ). Merus subtriangular in cross-section; outer and inner surfaces flat; outer lower margin usually with single spine at distal angle; inner lower margin with 2 or 3 distal spines. Carpus broad, much shorter than merus. Outer face with prominent submedian tubercle, occasionally with few additional smaller tubercles; distolateral margin with small granules or tubercles, spinetipped in juveniles. Upper margin with single terminal spine and, in smaller specimens, few additional posterior spines. Inner and lower faces smooth. Chela 0.9–1.6 as long as shield and 1.4–2.0 as long as width. Outer face of palm regularly convex, slightly tuberculate; upper margin with row of 6–8 spiny tubercles; outer lower margin rounded, smooth or slightly tuberculate. Inner face rounded, with tuft of setae below articulation of dactyl; inner lower margin somewhat angular with row of faint granules, prolonged by sharp row of tubercules on inner face of fixed finger. Fingers spooned at tips. Dactyl 0.6 time as long as entire chela, with tufts of long setae on lower margin; cutting edge with 2 or 3 large calcareous teeth on proximal 0.5. Fixed finger forming large hiatus with dactyl; cutting edge with large calcareous tooth on distal 0.5, and 1 or 2 smaller teeth on proximal 0.5.

Right cheliped shorter than left, reaching to base of fingers of left chela, or little beyond, when extended ( Fig. 1c View Figure 1 ). Merus compressed; upper margin sharp with few long setae; outer and inner lower margins each with 2 or 3 distal spines. Carpus much shorter than merus; outer face with median tubercle and 1 or 2 additional smaller ones; distal margin with several corneous-tipped tubercles, somewhat eroded in larger specimens, those proximate to upper and lower margins larger than others; upper margin with 3 strong spines, the distalmost one largest. Outer face of chela with distally plumose setae and several tubercles in distal upper half; upper margin with 5 strong corneous-tipped spines. Fingers spooned at tips. Dactyl 0.5 as long as whole chela; upper margin with a double row of 4 or 5 small corneous-tipped spines; cutting edge with two median calcareous teeth. Fixed finger with outer face tuberculate; cutting edge forming small hiatus with dactyl, armed with 2–4 triangular teeth.

P2 noticeably exceeding cheliped ( Fig. 1d View Figure 1 ). Merus as long as propodus; lateral and mesial faces compressed; dorsal and ventral margins with long, distally plumose setae; ventral margin with row of somewhat spiny granules; distolateral angle armed with single spine. Carpus 0.6 as long as propodus; lateral face inflated, mesial face flattened; dorsal margin with strong subdistal spine and smaller posterior spine; ventral margin with few plumose setae. Propodus feebly curved, subovate in cross-section, slightly shorter than shield length, with several tufts of long, distally plumose setae. Dactyl strongly curved, about 0.9 as long as propodus, terminating in strong corneous claw; ventral margin with few long simple setae, armed with 6–9 acute spines. P3 slightly overreaching tip of cheliped ( Fig. 1e View Figure 1 ). Merus about as long as propodus; lateral face smoothly curved; mesial face slightly concave; dorsal and ventral margins with several tufts of long, distally plumose setae; distolateral angle with spine. Carpus 0.7 times as long as propodus; dorsal and ventral margins with plumose setae; dorsodistal margin with strong terminal spine, sometimes with smaller additional posterior spine. Propodus 0.8 as long as shield length, subovate in cross-section, with tufts of long plumose setae mainly near dorsal and ventral margins. Dactyl as long as propodus; setation weak and similar to dactyl of P2; ventral margin with 7–9 acute spines.

Sternite of P3 with anterior lobe subrectangular; ventral surface swollen in 2 rounded projections, furnished with setae. Telson with left posterior lobe considerably larger than right; lateral margin armed with 8–10 spines, posterior margin with 3–6 spines ( Fig. 1f View Figure 1 ). Right posterior lobe regularly curved, without clear separation between posterior and lateral margins, armed with 6–8 spines.

Colour. After 18 months in alcohol, coloration still very clear on larg- er specimens. Shield orange, fading to white posteriorly. Posterior carapace white. Ocular acicle pink to orange, terminal spine white. Ocular peduncle with basal pink ring (almost white in smaller specimens), median orange area, and narrow white ring close to cornea. Antennular peduncle with dark orange blotches on proximal segment; median segment and proximal half of terminal segment orange; distal half of terminal segment pale blue to white; flagella yellow. Antennal peduncle orange on 4 proximal segments (spines white), yellow on terminal segment and flagellum.Antennal acicle orange with white at tips of spines. Cheliped with large irregular brown patches on pink to cream-white background. Outer and inner faces of merus with brown proximal and distal patches, separated by white median area; outer and inner faces of carpus with median subtriangular brown patches; outer face of chela with 2 brown median patches, a large one on the upper half and a smaller one along ventral margin; inner face of chela with 1 median brown patch. P2 and P3 with pink background. Lateral faces of meri, carpi and propodi with 2 orange brown stripes, forming 2 continuous lines on the 3 segments. Mesial faces with similar pattern, the 2 lines being less regular and reduced to elongated spots on meri and carpi. Dactyls with few elongated orange brown spots. Abdomen and telson white.

Distribution. Easter I.

Habitat. Hard bottoms, from shore to depth of 23 m. Gastropod shells used are: Coralliophila violacea , Nerita sp. , Planaxis akuana , Strombus maculatus , and perhaps also Erosaria caputdraconis , Fossarus cumingii , Neothais nesiotes , and Nodilittorina pyramidalis pascua (empty shells of these molluscs were found in vials containing loose crabs of different species).

Remarks. The holotype of Calcinus pascuensis was lost during the transfer of the Allan Hancock Foundation collections to the Los Angeles County Museum (G. Davis, pers. comm.). As the original description of the species was based solely on the incomplete holotype, a neotype has been selected herein.

A few morphological variations have been observed. In juveniles smaller than 1.6 mm the ocular peduncles are only 0.6–0.7 times as long as shield instead of 0.8–1.0 in larger specimens. The ocular acicle has typically a single terminal spine on 17 specimens out of 20, but a few other armaments have been observed: 1 additional spinule, unilaterally; two terminal spines on each acicle; and two spines on one acicle and three on the other. The left chela presents several variations according to sex or size. It is usually shorter in females, only 0.9–1.1 times as long as shield versus 1.0– 1.6 in males. The aspect of its upper margin varies from almost smooth to armed with a row of six to eight spines. These spines are more acute in juveniles and also cover the upper half of the outer face of the chela. The armament of the telson varies with size. In specimens larger than 3.0 mm, it consists of 11–16 spines on the left posterior lobe and six to eight on the right posterior lobe. In smaller specimens the number of spines is reduced to two to eight spines on the left posterior lobe and two to three spines on the right posterior lobe.

In armament of the ocular acicle (simple) and telson (several spines on both posterior lobes), aspect of outer face of the left chela (regularly convex), and similar sparse pilosity on distal P2 and P3, Calcinus pascuensis is most similar to C. inconspicuus Morgan, 1991 . However, the two species are easily differentiated by coloration: chelipeds, P2 and P 3 in C. inconspicuus are almost uniformly coloured while in C. pascuensis there are patches on the chelae and stripes on P2 and P3. They also differ in armament of the telson, the spines of the left posterior lobe being present only on the posterior margin in C. inconspicuus , whereas they are on the posterior and lateral margins in C. pascuensis .

Calcinus pascuensis View in CoL is distinguishable from the other Indo-West Pacific species by the remarkable coloration of walking legs. A similar pattern is observed in C. anani Poupin and McLaughlin, 1998 View in CoL , but the stripes on the propodi and dactyls merge in an intricate network of reticulations. Calcinus pascuensis View in CoL is also unique in the setae on the outer face of the right chela, and on the dorsal and ventral margins of P2 and P3. These setae are distally plumose, which give them a club-like aspect ( Fig. 1 g View Figure 1 ). Although plumose setae are sometimes observed in other species, they are not club-like shaped and are inserted only on the distoventral margins of P2 and P3.