A new hermit crab of the genus Calcinus from Rapa Island, French Polynesia with affinities to Calcinus dapsiles Morgan, 1989 and Calcinus sirius Morgan, 1991 (Decapoda: Anomura: Diogenidae)

Solitary Islands, Eastern Australia, has shown that the specimen from Rapa Island is distinct from Morgan’s taxon and represents a new species which is fully illustrated and described herein as Calcinus shawi sp. nov. The morphology and coloration of this new species are compared with the closely allied C. sirius and Calcinus dapsiles Morgan, 1989.

in a new family Calcinidae Fraaije, Van Bakel and Jagt, 2017. However, until cephalothoracic groove patterns and numerous other body characters, as well as genetic data, are fully evaluated in Recent species across the Diogenidae, the use of the latter family is maintained for Calcinus. Specimens used in this study remain deposited in the Australian Museum, Sydney  Not C. sirius Morgan, 1991. New Calcinus hermit crab from Rapa Island Nauplius, 30: e2022014  Diagnosis. Ocular acicles terminating in simple spine (Fig. 1B, B'). Left chela, largest (Fig. 1A, C) 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 corneous-tipped spines (Fig. 1A, D). Dactyl of P2 (Fig. 1E, F) slightly shorter than propodus, with 10 movable spines on ventral margin. Dactyl of P3 (Fig. 1G) slightly shorter than propodus, with 7 movable spines on ventral margin. Ventrodistal pilosity of P3 weak, slightly denser than that of P2 ( Fig. 1F, G). Telson with posterior lobes each armed with single terminal spine (Fig. 1H). Overall live color orange, paler on ocular peduncles, without colored stripes or spots; eggs bright red.
Description. Shield 0.85 times as broad as long. Rostrum (Fig. 1B, B') triangular, slightly overreaching level of broadly subtriangular lateral projections; anterior margins between rostrum and lateral projections concave. Anterodorsal plate of branchiostegite with dorsal margin nearly smooth, with few spinules on proximal half.
Antennular peduncles reaching to distal 0.25-0.30 of right ocular peduncle. Ultimate segment 0.38 times as long as shield. Antennal peduncles shorter than antennular peduncles, reaching between midpoint and distal one-third of right ocular peduncle. First segment with ventrolateral angle produced, bearing 2 or 3 spines. Second segment with laterodistal angle produced, terminating in bifid spine; distomesial angle with minute spine. Third segment with strong spine at ventrodistal angle. Fourth segment with dorsodistal spine. Fifth segment unarmed. Antennal acicle reaching beyond proximal margin of fifth antennal segment, terminating in strong spine; dorsolateral margin with spine distally, dorsomesial margin with row of spines.
Left chela larger than the right, (Fig. 1C), 0.74 times as high as long. Dactyl 0.55 times palm length; cutting edge with 2 subtriangular calcareous teeth on proximal half; dorsal margin granulated. Fixed finger with 3 triangular teeth on proximal half of cutting edge; outer and lower faces with granules. Palm with outer face regularly convex, without depressions, coarsely granular; inner face smooth; upper margin of palm with a row of 7 blunt spines and a few accessory tubercles in between. Carpus with prominent submedian tubercle on outer face; upper margin with 1 or 2 small indentations and 1 strong spine at dorsodistal angle. Merus stout, triangular in cross-section; ventromesial margin with few spines distally; ventrolateral margin with 2 spines distally; upper margin unarmed.
Right chela smaller than left (Fig. 1D), with 6 corneous spines on upper margin of palm. Dactyl about as long as palm; cutting edge with 3 triangular teeth on proximal half; dorsal surface with 2 subparallel rows each of 5 or 6 spines; fixed finger with 1 large triangular tooth on cutting edge, proximally, outer face with tubercles, those near tip bearing setae. Palm with outer face weakly convex, smooth on proximal two-thirds, tuberculated distally, near base of fingers; inner face flat, smooth. Upper margin of carpus with 2 or 3 spines increasing in size distally. Merus similar to that of left cheliped.
Ambulatory legs similar from left to right. P2 (Fig. 1E, F) exceeding left cheliped by length of dactyl when fully extended; dactyl 0.81 times as long as propodus; ventral margin with widely-spaced, sparse tufts of setae and 10 minute spines; propodus with few long setae, and minute movable spine at ventrodistal angle; carpus 0.60 times as long as propodus, with strong dorsodistal spine; merus slightly longer (1.06 times) than propodus, with lateroventral spine distally. P3 (Fig. 1G) shorter than P2, overreaching tip of left cheliped by distal half of dactyl when fully extended; ventrodistal pilosity not brush-like and only slightly denser than that of P2; dactyl shorter (0.85) than propodus, ventral margin armed with 7 minute spines; propodus unarmed on ventral and dorsal distal angles; carpus 0.68 times as long as propodus, New Calcinus hermit crab from Rapa Island Nauplius, 30: e2022014 with dorsodistal spine; merus slightly shorter (0.96 times) than propodus, with indistinct lateroventral spine, distally. Fourth pereopod semichelate; dactyl terminating in corneous claw, ventrolateral margin with row of spinules; propodus with broad rasp consisting of several rows of corneous scales; carpus with dorsodistal spine; merus unarmed, ventral margin with long setae. Fifth pereopod chelate, with rasp on propodus and dactyl; carpus and merus unarmed, subovate in cross-section.
Abdomen with 4 unpaired biramous left pleopods. Sixth abdominal tergite calcified, with dorsal face divided into 4 subequal areas by longitudinal and transverse furrows. Telson with posterior lobes asymmetrical (Fig. 1H), left more elongated than right; lobes with long setae marginally, each with 1 posterior spine slightly curved ventrally.
Live color (Fig. 1A). Shield and posterior carapace orange. Ocular peduncles pale orange on proximal third, fading gradually to white on distal two-thirds. Antennular peduncles orange, becoming pale on distal fourth of terminal segment; flagella orange. Antennal peduncles orange, with white-tipped spines; flagella orange. Chelipeds bright orange. Ambulatory legs orange, a little darker at setal pores. Abdomen redbrown; eggs bright red.
Distribution and habitat (Fig. 4). So far known only from Rapa Island, Austral Islands, French Polynesia; dredged at 100 m on hard bottom of rocks and corals.
Etymology. Named in honor of Ian Shaw, who took the first color photographs of Australian specimens of C. sirius, which made possible the determination of the characters that distinguish that species from this new one.
Remarks. Calcinus shawi sp. nov. and three other IWP species, C. albengai, C. dapsiles, and C. sirius, share the following characters: 1) ocular acicle with a single terminal spine; 2) spinose upper margin of right chela; 3) regularly convex outer face of left chela, lacking depressions; 4) single posterior spine on left lobe of telson; 5) without distinct brush of setae on ventral margin of P3. The latter three species were included in Malay and Paulay's (2010, fig. 14) Clade X along with the ESU C. aff. albengai, the shallow water (< 50 m) color variant of the deep water (50-280 m) C. albengai, and two species having a distal brush of setae on the ventral margin of P3, Calcinus argus Wooster, 1984, and Calcinus anani Poupin and McLaughlin, 1998. Subsequently, Malay et al. (2012 have found that Poupin and McLaughlin's (1998) C. anani is restricted to French Polynesia, and described C. fuscus from Japan and western Pacific. The photograph of C. anani from Japan in Malay and Paulay (2010, fig 14) and their sequences of C. anani from Bismarck archipelago, Papua New Guinea (UF4808), actually represent C. fuscus.
Calcinus shawi can be easily separated from all species of Malay and Paulay's (2010) Clade X by their color patterns. Live colors of C. anani and C. fuscus are illustrated in Malay et al. (2012, fig. 2) and that of C. albengai, C. aff. albengai, and C. argus in Poupin and Lemaitre (2003, fig. 1) and Hoover (1999: 253). Additional photographs can be found in the Internet databases of Legall and Poupin (2021) and Myorin (2021). In C. shawi the ambulatory legs are overall uniformly orange (a little darker at setal pores), while most other species of Clade X have a pattern of spots or lines on the ambulatory legs. Calcinus albengai, C. aff. albengai, and C. argus have the ambulatory legs punctuated with white spots. Calcinus fuscus and C. anani have a pattern of reticulated lines forming elongated oval patches on propodi and dactyls.
Calcinus shawi sp. nov. cannot be confused with any other Calcinus species that are not in clade X. All of them are different by their color pattern and/ or by morphological characters presented in the key of Poupin and McLaughlin (1998) including: several distal spines on the ocular acicle and/or lobes of telson; external face of the right palm not regularly convex; dorsal margin of the right chela smooth; and distal setation of P3 more pronounced than that of P2, sometimes forming a brush of setae.
Calcinus shawi sp. nov. is closely related to two Australian species also in Malay and Paulay's (2010) Clade X and reported from similar latitudes in the southern hemisphere, C. dapsiles from WA and C. sirius from EA. The live coloration of the C. dapsiles was previously known by the color photograph in Jones and Morgan (2002: 116), whereas that of C. sirius has only now been discovered by the first author in the New Calcinus hermit crab from Rapa Island Nauplius, 30: e2022014 'Hermit crab visual dictionary' managed by Myorin (2021). The differences in coloration of these three species, which can be useful in their identification, are contrasted below under the discussion of C. dapsiles and C. sirius. Morgan, 1989 ( Figs. 2A-D, 4) Calcinus dapsiles Morgan, 1989: 407   dactyl of P2 as long as propodus with row of 6-8 short corneous spines on ventral margin, instead of shorter than propodus (× 0.81) with row of 10 minute spines on the ventral margin in C. shawi sp. nov.

Calcinus dapsiles
Live color (Fig. 2). The live coloration of Calcinus dapsiles (Fig. 2) cannot be confounded with that of C. shawi sp. nov. which is overall orange without remarkable markings (Fig. 1). The ground color of C. dapsiles is chocolate brown to pink with white on fingers of chelae and distal parts of ambulatory dactyls and propodi. The ocular peduncles are pink on proximal half turning to chocolate brown distally with a thin cream band at base of corneas. In C. shawi sp. nov. the ocular peduncles are pale orange on proximal one-fourth fading to white on distal part without distal band at base of corneas. Morgan New Calcinus hermit crab from Rapa Island Nauplius, 30: e2022014 (1989: 411) indicates that Calcinus dapsiles can be "readily recognized in the field by its distinctive red and white colour patterns, together with the small reddish spots on the chelipeds and walking legs".
Distribution and habitat (Fig. 4). Calcinus dapsiles is one of the most common and ubiquitous shallow water hermit crabs in WA (Morgan, 1989;1991). Its geographic distribution is plotted in Fig. 4 based on localities reported by Morgan (1989;1991), Poore et al. (2008), McEnnulty et al. (2011, photographs studied during the present study, ALA (2021a) and CSIRO (2021) databases, and specimens deposited in MV collections (Material examined). This species is known with certainty only from WA, including Houtman Abrolhos Islands, between latitudes 22-35°S. Morgan (1991) indicates a depth range of 0-97 m, slightly extended herein to 102 m, from collections of the Southern Surveyor voyage SS10-2005 (off Two Rocks, MV J 54753, J 55372, J 54755).
A doubtful record in Central Bass Strait, 65 km ENE of Cape Rochon, Three Hummock Island, 75 m, -40.1817 145.738 (MV J 52817) is out of the usual range for this species. A re-examination by G. Poore, at the end of this study, confirms that the setation of P2 and P3 is scarce, similar for both legs, different from C. dapsiles where distal setation of P3 is more pronounced than on P2. It is however a juvenile that has lost its color. In the future, it will be interesting to confirm the presence of C. dapsiles in Bass Strait with adults and colored specimens. According to O'Hara and Poore (2000) the species richness of southern Australian marine fauna graded with latitude from high diversity in the warm temperate regions around Perth and Sydney to low diversity in cool temperate southern Tasmania. This would be an indication that C. dapsiles perhaps does not occur south of 35°S, its ultimate confirmed WA latitudinal occurrence. Conversely, a disjunct distribution, such as it is presented in Fig. 4 for C. dapsiles (WA and Bass Strait), has also been reported by Poore et al. (2008: 3, fig. 2) for the slipper lobster Ibacus alticrenatus Spence Bate, 1888, attributed to the scarcity of collections in the Great Australian Bight, and an indication that C. dapsiles would be indeed present in Bass Strait.
Remarks. To our knowledge, the only color photograph published for C. dapsiles previous to the present study was that in Jones and Morgan (2002, of a specimen from WA but without further detail of location). Our study of color photographs (Fig. 2B, C) obtained by scuba divers operating in the Perth area and included in Myorin (2021), as well as additional color photographs in the Atlas of Living Australia (ALA, 2021a), confirmed the remark by Morgan (1989) that C. dapsiles is abundant in south-western Australia, and is the only species of Calcinus that occurs south of the Rottnest Island (32°S) in that region. It is morphologically related to C. shawi sp. nov. but differs in a few morphological differences (see Affinities) and live coloration (compare Figs. 1 and 2). The two species have also been sequenced by Malay and Paulay (2010), and their molecular data confirm the genetic separation of these two species. Morgan, 1991 (Figs. 3A-D, 4) Calcinus sirius Morgan, 1991: 899, figs (Randall, 1840). Calcinus tibicen. -Heller, 1865: 87 [in part, Sydney, 1 juvenile, SL = 0.92 mm, NHMW 19588]. According to McLaughlin and Dworschak (2001: 154), this juvenile is possibly C. sirius Morgan. Not C. tibicen (Herbst, 1791). Affinities. Overall this species is similar to C. shawi sp. nov., with the following differences: dactyl of left larger chela (male) approximately as long as upper margin of palm, instead of noticeably shorter (× 0.55) as in C. shawi sp. nov.; upper margin of left larger palm (in male) with row of low tubercles, instead of having 7 blunt spines in C. shawi sp. nov.; ventral margin of dactylus and propodus of P3 with greater development of setae than on P2 but not forming a brush of setae, whereas in C. shawi sp. nov. the setation density is similar on P2 and P3.

Calcinus sirius
Live color (Fig. 3). Shield cream, with darker orange anterior and anterolateral margins. Ocular peduncles pink to violet on proximal half, grading to paler distally without thin cream band at base of corneas; corneas black with large white spots. Distal antennular peduncles and flagella orange. Antennal peduncles and flagella orange. Chelipeds with fingers and palm cream to pale orange with a few minute scattered red dots; carpus and merus deep orange with white at tip of spines and tubercles. P2 and P3 uniformly orange with minute scattered red dots but without reticulation or spots, dactylus deep orange, propodus deep orange proximally fading to paler distally, carpus and merus pale orange or orange.
Remarks. The color photographs examined for the present study were taken at a depth of 8-15 m in the Solitary Islands (North, Northwest, and South), about 5-10 km offshore in EA. According to the photographer, Ian Shaw, this species is commonly seen throughout the year. Its geographic limit has been greatly extended by Ahyong (2015) to the East, to Kermadec Is. Poupin and Lemaitre (2003) had speculated that C. sirius could reach Rapa I., still more to the East (Fig. 4), if the live coloration of C. sirius and C. aff. sirius were shown to be the same. The present study has shown that this is not the case, and that C. sirius and C. shawi sp. nov. have different distinctive coloration. Possibly, the latter new species evolved from the former by allopatric speciation. For the time being C. sirius appears to live in shallow waters (2-27 m; never reported during the numerous deep-water expeditions organized off eastern Australia), whereas C. shawi sp. nov. lives deeper (100 m; not found in shallow waters also surveyed during BENTHAUS campaign). However, as reported in this study for C. dapsiles, known from 0 to 102 m, the depth range of species of Calcinus can be wide and depth distributions of the species are still not known accurately because of the vagaries of collections and too fragmentary data.
The live color photographs of C. sirius make it also possible to remove the doubt of a potential synonymy between C. anani (and sibling C. fuscus) with C. sirius suggested by Poupin and McLaughlin (1998: 11) and Asakura (2002: 34-35), the latter author indicating that "it is highly probable that C. anani [also C. fuscus] and C. sirius are conspecific. However, until the living coloration of the ambulatory legs of C. sirius can be observed, this problem cannot be resolved". The color photographs examined herein confirm that no reticulations are seen in live color of C. sirius and that it is distinct from C. anani and its sibling-species C. fuscus.  acKnOwledgements We gratefully thank Ian Shaw and Eiji Myorin. Ian Shaw took the color photographs of the new species and generously granted us the right to use them in our contribution. Eiji Myorin, webmaster of the remarkable 'Hermit crab visual dictionary', drew our attention to these photographs and put us in touch with I. Shaw. Thanks also to the other photographers that have granted us the right to use their live color photographs of Calcinus dapsiles -Karen Gowlett-Holmes, working for CSIRO, Matthias Liffers, and Rokus Groeneveld. Gary Poore also helped with literature, a list of specimens deposited in MV collections, re-examination of specimens and several useful comments.