Calaxius poupini Komai, 2016, n. sp.
Creators: name: Komai, Tomoyuki
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Axiidae
Calaxius
Calaxius poupini

description: Calaxius poupini n. sp.
Figs 1–3
Material examined. Holotype: TARASOC, stn CP3376, W of Raitahiti, 15°41’S, 146°54’W, 646–737 m, 4 October 2009, female (cl 9.1 mm), MNHN-IU-2011-5124.
Paratypes: same data as holotype, 1 male (cl 8.7 mm), 2 females (damaged), 1 ovigerous females (cl 9.4 mm), MNHN-IU-2014-12783; same data, 1 ovigerous female (cl 6.9 mm), CBM-ZC 13264.
Diagnosis. Rostrum slender, reaching distal margin of second segment of antennular peduncle, each lateral margin bearing 1–3 small spines. Carapace surface nearly smooth; gastric region with median carina bearing 2–4 tiny denticles or tubercles followed by 1 low convexity; submedian carinae each with 2–4 tubercles or denticles; lateral carinae each divided in 2 parts, anterior part with 1 conspicuous spine (supraocular spine), posterior part terminating anteriorly in small tubercle or spine; trace of postcervical median carina discernible near posterodorsal margin. Second to fourth pleura all rounded, posteroventral margin of fifth pleuron slightly angular. Telson with 2 pairs of tiny spines and 1 pair of small spiniform setae on lateral margins; posterolateral angles each with 2 unequal submarginal spiniform setae; dorsal surface with 2 pairs of spines. Eyestalks not reaching midlength of rostrum, cornea pigmented. Antennal scaphocerite reaching tip of rostrum. Chelipeds subequal in length and slightly dissimilar in armature; ischia each with 1 strong spine subdistally; meri each with 1 small subdistal spine on dorsal margin, ventromesial margin unarmed or armed with 1 small spine followed by 0–3 tiny spines or denticles; chelae each with dactylus longer than palm, particularly setose on dorsal palmar surface and lateral surface of fixed finger, each with 3 or 4 moderately large spines on dorsal margin of palm.
Description. Holotype female. Rostrum (Fig. 1 A, B) reaching distal end of second segment of antennular peduncle, 0.3 times of distance between rostral base and cervical groove or 0.2 times as long as carapace, slender, tapered to acute tip; lateral margin with 2 (right) or 3 (left) asymmetrically arranged, small subacute teeth and 1 prominent supraocular spine, continuous with sharply delimited lateral gastric carina on carapace; dorsal surface shallowly concave. Carapace (Fig. 1 A–C) nearly smooth on surface, but with sparse very short setae on lateral gastric region and brachial region; dorsal surface nearly straight in lateral view, gastric region slightly sloping down to rostrum; median gastric carina distinct, extending anteriorly beyond rostral base and not reaching to cervical groove, with 2 small, unequal tubercles plus obtuse convexity anterior to midway between rostral base and cervical groove; submedian carinae parallel, bearing 2 (left) or 4 (right) tubercles; lateral gastric carinae extending beyond midway between rostral base and cervical groove, divided into two widely separated parts, anterior part without armature other than supraocular spine, posterior part terminating anteriorly in small denticle, but otherwise unarmed; 1 small tubercle present on space between median and submedian carinae slightly anterior to the anterior end of submedian carina; trace of postcervical carina discernible in posterior part; cervical groove distinct, extending to pterygostomial region; suborbital lobe broadly rounded; pterygostomial margin slightly produced, broadly rounded.
Seventh thoracic sternite with shield (Fig. 2 A) divided into two sections by distinct transverse ridge; anterior section subtriangular, slightly depressed below; posterior section deeply divided in midline, each lateral angle produced in subacute tooth directed ventrally.
Pleon (Fig. 1 D) with some tufts of setae on each somite. First pleomere (Fig. 1 C) widened posteriorly, anterodorsal margin excavate; pleuron triangular with subacute tip, produced slightly beyond ventral margin of second pleuron. Second pleuron slightly asymmetrical; lateral surface with shallow depression; ventral margin unarmed, rounded at either angle. Third to fifth pleura rounded. Sixth pleuron broadly rounded ventrally, with blunt posterolateral projection. Telson (Fig. 1 E) subrectangular, 1.4 times as long as wide; lateral margin with low convexity proximally, 2 tiny spines in anterior half and 1 small spiniform seta slightly posterior to midlength; posterior margin convex without posteromedian spine, fringed with numerous long setae, posterolateral area with 2 unequal spiniform setae (outer seta missing on right side); dorsal face shallowly sulcate medially, armed with 2 pairs of spines, anterior spine located at anterior 0.4 and posterior spine at midlength; long setae arising at bases of these dorsal spines.
Eyestalk (Fig. 1 A, B) about 0.4 length of rostrum; cornea hemispherical, subequal in length and width to eyestalk, darkly pigmented. Antennular peduncle (Fig. 1 A, B) reaching distal margin of fourth segment of antennal peduncle; statocyst lobe on first segment unarmed; flagella slightly longer than carapace. Antennal peduncle (Fig. 1 A, B) with first segment bearing 1 tiny spine at ventromesial distal angle and 1 longer spine on ventrodistal margin medially; second segment with straight dorsolateral distal spine reaching beyond midlength of scaphocerite; scaphocerite simple, acuminate, slightly overreaching midlength of fourth segment; third segment with 1 conspicuous spine at ventromesial distal angle; fourth segment slightly longer than second segment (except for dorsolateral distal tooth); fifth segment about half length of fourth segment; flagellum exceeding 3 times as long as carapace.
Third maxilliped (Fig. 2 B) moderately slender. Coxa with bifid spine at ventrodistal angle. Basis with 1 spine at ventrodistal angle. Ischium (Fig.) with distomesial angle produced into strong, incurved tooth, crista dentata consisting of row of sharp teeth (distal 9 teeth subequal in size, proximal denticles small, decreasing in size); ventral margin with 2 tiny denticles in proximal half. Merus with 3 spines on ventral margin noticeably increasing in size distally. Carpus with 1 minute spine at ventrolateral distal angle. Dactylus slightly shorter than propodus. Exopod consisting of 2 articles, reaching distal margin of merus; distal article flagellum-like.
Chelipeds subequal in length, almost similar; meral-carpal articulation with about 30° of torsion (left with clockwise torsion, right with counter clockwise torsion). Left cheliped (Fig. 3 A–C) with coxa unarmed. Basis also unarmed. Ischium with 1 prominent subdistal spine and 1 minute denticle on ventral margin. Merus with dorsal margin strongly convex, sharply carinate, with 1 small subdistal spine followed by row of setae in distal half; lateral face glabrous, convex, distoventrally with excavation delimited with 2 small subdistal tubercles and following keel-like convexity (this excavation fitting flexor margin of carpus, when cheliped flexed); mesial face smooth, flattish; ventral margin bicarinate, lateral carina unarmed and becoming obsolescent distally, while mesial carina with 1 small but conspicuous spine arising distal to midlength, but otherwise smooth. Carpus higher than long, dorsal margin with sharp, denticulate carina and with 2 small subdistal spines and numerous long setae; lateral face with sparse tufts of short to long setae, and with sharp longitudinal keel along ventral margin; mesial to ventral surface glabrous, latter inflated to form protuberance. Chela massive. Palm nearly as long as high; dorsal surface non-carinate, armed with 4 widely spaced, moderately strong spines and scattered tubercles, these armature partially obscured by numerous tufts of long plumose setae; lateral surface flattish, with few small spines or tubercles, including one conspicuous spiniform tubercle proximal to base of fixed finger, and sparse tufts of short to long setae; ventrolateral margin sharply keeled over entire length including fixed finger; distolateral margin forming flange-like keel overhanging base of dactylus; mesial face inflated, with tufts of long setae along dactylar articulation and 1 rounded tubercle somewhat proximal to base of fixed finger. Fingers crossing each other, each terminating in acute tip; narrow hiatus leaving proximally when closed. Fixed finger with slightly arcuate ventral margin; occlusal margin with 1 small but conspicuous, acutely triangular tooth at midlength and otherwise minutely or faintly denticulate; lateral surface obscured by numerous tufts of long plumose setae; mesial face with thin, simple setae ventrally and tufts of short to long plumose setae adjacent occlusal margin. Dactylus about 1.2 times as long as palm, nearly straight with curved tip, with numerous tufts of long plumose setae on non-carinate, unarmed dorsal margin and lateral surface; both lateral and mesial surfaces elevated in midline as blunt ridge in proximal half; occlusal margin without conspicuous teeth, with faint denticulation proximally; narrow hiatus between fingers when dactylus closed.
Right cheliped (Fig. 3 D, E) with ischium bearing 2 minute denticles in addition to prominent subdistal spine on ventral margin. Merus unarmed on ventral margin. Carpus with 1 small subdistal spine on dorsal margin. Palm with 4 spines on dorsal margin; lateral face with 1 conspicuous spiniform tubercle proximal to base of fixed finger in addition to few small tubercles; flange-like plate at dactylar articulation less developed than in left, its margin slightly denticulate; mesial face without conspicuous tubercle proximal to base of fixed finger. Fixed finger with 1 triangular tooth at midlength and 1 smaller, subdistal tooth on occlusal margin. Dactylus 1.3 times as long as palm.
Second pereopod (Fig. 2 C) relatively slender. Ischium unarmed. Merus with 3 small denticles on ventral margin. Carpus 0.9 times as long as chela. Chela with fixed finger slightly deflexed; dactylus about 0.4 times as long as palm; occlusal margins of fingers each with row of minute spiniform setae. Setation typical for genus.
Third pereopod (Fig. 2 D, E) relatively slender, unarmed on ischium and carpus. Merus with 3 widely spaced, minute denticles on ventral margin. Propodus with 5 comb-like, transverse sets of spiniform setae and row of numerous spiniform setae on distal margin. Dactylus gently curving, terminating in tiny, basally demarcated unguis; lateral surface with row of small spiniform setae adjacent to extensor margin and row of minute spiniform setae on flexor margin; mesial face unarmed. Setation typical for genus.
Fourth pereopod (Fig. 2 F, G) unarmed on ischium to carpus. Propodus with 6 transverse sets of spiniform setae on lateral face; distal margin also with row of spiniform setae. Dactylus about 0.4 times as long as propodus, slightly twisted proximally and gently arcuate, terminating in basally demarcated unguis; lateral surface with row of spiniform setae adjacent to extensor margin (1 spine at midlength not aligned) and row of minute spiniform setae on flexor margin; mesial face unarmed.
Fifth pereopod (Fig. 2 H, I) not chelate or semichelate, unarmed on ischium to carpus. Propodus slightly widened distally, bearing obliquely longitudinal line of grooming setae in distal half; flexor distal part slightly produced, bearing spiniform setae on subtruncate terminal margin. Dactylus lanceolate, terminating in basally demarcate, acute unguis, somewhat twisted; extensor surface with stiff setae; flexor surface excavated proximally; inner surface with several spiniform or stiff setae adjacent to extensor margin; sinuous flexor margin with row of minute spiniform setae in distal half.
First pleopod two-segmented, uniramous. Second to fifth pleopods narrow, each with well-developed, rod-like appendix interna.
Uropod (Fig. 1 F) with endopod about twice as long as wide, bearing 3 small spines on posterior half of lateral margin (posterolateral spine largest); median ridge on dorsal surface with row of 3 spines in distal half, posteriormost spine submarginal, reaching beyond posterior margin (left) or only with 1 spine far proximal to posterior margin (right). Exopod subequal in length to endopod; lateral margin slightly convex, with 3 tiny spines on posterior 0.3, and with 2 spiniform setae at posterolateral angle; middorsal ridge unarmed, obsolete lateral ridge with tiny spinules in double row; transverse suture serrate with row of spinules.
Paratypes. Rostrum with 1 or 2 small lateral spines. Gastric median carina fading away somewhat anterior to cervical groove, with 2–4 small anterior denticles followed by 1 low convexity; submedian carina 2–4 denticles. Third maxilliped with ischium unarmed or bearing 1 minute denticle on ventral margin; merus with 2 spines on ventral margin. Cheliped meri bearing 1 conspicuous spine followed by 0–3 smaller spine or tiny denticles; palm with 3 or 4 spines on dorsal margin. Merus of second pereopod with 2 or 3 minute denticles or spines on ventral margin. Merus of third pereopod unarmed. Male second pleopod (Fig. 2 J) appendix masculina slender, subequal in length to appendix interna, bearing several long setae on terminal to distal half of dorsal margins. Uropodal endopod with 4 or 5 spines on lateral margin and 4 or 5 spines on median ridge; exopod with 4 spines on lateral margin and 1 spiniform seta at posterolateral angle.
Gill formula, examined with one paratype (damaged female), summarized in Table 1. All gills but arthrobranch on second maxilliped well lamellate; arthrobranch on second maxilliped rudimentary, simple. Pleurobranch present above base of second to fourth pereopods. Two arthrobranchs on third maxilliped to fourth pereopods. Epipods on first maxilliped to fourth pereopod, those on third maxilliped to third pereopod each with podobranch, those on first and second maxillipeds and fourth pereopod devoid of podobranch. Setobranchs on first to fourth pereopods well developed, each consisting of tuft of long setae inserted in gill chamber.
Coloration in life. Unavailable.
Distribution. At present, known only from the type locality in French Polynesia, at depths of 646– 737 m. Remarks. Kensley & Hickman (2001) suggested that species of Calaxius fall into two broad groups, viz., those with strongly triangular and ventrally acute pleura of pleomeres and those with ventrally rounded pleura. Calaxius poupini n. sp. is characterized by the rounded second to fifth pleonal pleura, and in this regard, it is grouped with C. euophthalmus, C. inaequalis, C. galapagensis, C. izuensis, C. jenneri, C. kensleyi, C. mimasensis, C. pailoloensis, and C. sibogae. Among the latter nine species, C. inaequalis and C. jenneryi can be eliminated from further comparison because of exceptional features for the genus: C. inaequalis and C. jenneri are unusual in having elongate eyestalks reaching the rostral apex (cf. Rathbun 1901; Williams 1974), and in particular, the former species is unique in having “dumbbell-shaped” eyestalks; C. jenneri is characteristic in having markedly dissimilar chelipeds (Williams 1974). Although C. galapagensis closely fits the generic diagnosis of Calaxius given above, it is unique in the strongly tridentate rostral apex and the strongly spinose gastric carinae on the carapace (Kensley & Hickman 2001).
Calaxius euophthalmus is closely similar to C. poupini n. sp. Nevertheless, comparison with the extensive description of the holotype by De Man (1925) reveals some morphological differences. The telson bears two pairs of lateral spiniform setae in C. euophthalmus, rather than only one pair in C. poupini n. sp. The palm of each cheliped has only two small spines on the dorsal margin in C. euophthalmus (cf. De Man 1925, pl. 10, fig. 22e), whereas there are three or four moderately strong spines in C. poupini. Finally, the ventral margin of the cheliped merus is clearly serrated with two spines and seven tubercles in C. euophthalmus (cf. De Man 1925, pl. 10, fig. 22f), rather than unarmed or armed with only one or two spines and one to three minute denticles in C. poupini n. sp.
Calaxius izuensis may be most similar to C. poupini n. sp. The former differs from the new species in the dissimilar chelipeds of which the palm of the major side has scattered small tubercles on the mesial face, the spinose or serrate ventral margin of the cheliped meri and the fingers of the major cheliped being distinctly shorter than the palm (Komai 2011). In C. poupini, the chelipeds are almost similar from right to left in the stoutness; no scattered tubercles are present on the mesial face of the cheliped palm; the fingers of the chelipeds are clearly longer than the palms in both sides.
Calaxius kensleyi differs from the new species in the minutely granulate and punctate surface of the carapace (versus smooth), two small spines on the median gastric carina (versus one to four small denticles plus one convexity), the second pleonal pleura with a distinct posteroventral point (versus rounded), strongly spinose ventral margin of the cheliped merus and the absence of dorsal spines on the uropodal exopod (versus with some small spines on the dorsolateral ridge) (Clark et al. 2007).
Calaxius mimasensis is readily separable from C. poupini n. sp. by the gastric carinae on the carapace having much more numerous tubercles or denticles, the presence of intercarinal granules or tubercles on the gastric region of the carapace (versus absent), meri of the chelipeds each having two to four spines on the dorsal margin (versus only one spine is present) and a strongly spinose ventral margin (Komai et al. 2002).
Although Rathbun’s original description of Calaxius pailoloensis (as Axius) is insufficient to the modern standard, Sakai & de Saint Laurent (1989) presented a figure of the holotype of C. pailoloensis, which helped me to assess diagnostic characters of that species. Calaxius pailoloensis differs from the new species in the posteroventrally bluntly pointed pleura of the second and third pleomeres (versus rounded) and the strongly spinose ventral margin of the cheliped merus (Sakai & de Saint Laurent 1989: Fig. 22). Sakai & de Saint Laurent (1989) illustrated a distinct median carina extending from the midlength of the rostrum beyond the cervical groove on the carapace, but one of the two reviewers kindly informed me that the illustration is not correct in this regard. De Man (1925) gave a detailed description of a single young female specimen from Indonesia he identified with C. pailoloensis, but he questioned his identification because of the presence of inconsistencies in some characters when compared with the original description by Rathbun (1906). Therefore, De Man’s (1925) description is not referred.
Calaxius sibogae is known with certainty only by the holotype (see below). Comparison with the extensive description by De Man (1925) reveals several morphological differences between the two species. Calaxius sibogae differs from C. poupini in the elongate rostrum overreaching the distal margin of the second segment of the antennular peduncle (versus not overreaching it), much stronger lateral spines on the rostrum, the pitted lateral surface of the carapace (versus smooth), and the unusually slender third maxilliped of which the merus is armed only with one spine on the ventral margin (versus the merus is armed with two or three teeth noticeably increasing in size distally) (De Man 1925). The shape and armature of the chelipeds are also substantially different between the two species. In C. sibogae, the ventral margin of the merus is armed with three large spines; the carpus is armed with one or two spines on the ventrolateral keel; fingers are more elongate, being about 1.5 times as long as the palm, of which the fixed finger is armed with four large, acute teeth on its occlusal margin. In C. poupini, the ventral margin of the merus is unarmed or armed with one small spine; the dorsal margin of the carpus is unarmed on the ventrolateral keel; fingers are 1.1–1.2 times as long as the palm; the occlusal margin of the fixed finger is armed only with one or two small teeth.
Comments on the account of “ Manaxius ” euophthalmus by Sakai (2011) would be necessary. Sakai (2011: 134) reported Calaxius euophthalmus (as Manaxius) along with the holotype and additional material, but his account is surprisingly confusing. In the material examined section, he listed the holotype (as lectotype) from Indonesia (Zoological Museum, University of Amsterdam, ZMA Crust. De. 240080), one specimen from French Polynesia identified with C. sibogae by Ngoc-Ho (2005) (MNHN-Th 1421), and specimens identified with Manaxius pitatucensis by Kensley (2003), viz., one specimen from Okinawa, Japan (National Museum of Natural History, Smithsonian Institution, USNM 243379), and three specimens from Guam, Mariana Islands (USNM 243378, 243380, 243381). As mentioned above, Sakai (p. 131) regarded Kensley’s material also as a new taxon M. aganaensis, though the name is not available. It is unlikely that Kensley’s specimens represent C. euophthalmus, because they differ from C. euophthalmus by the subacutely pointed pleura of the second to fifth pleomeres. Sakai’s (2011) identification of the specimen studied by Ngoc-Ho (2005) also needs to be verified considering the confusing identification by him. Therefore, Sakai’s (2011) account of C. euophthalmus should be referred with great caution.
Of the 14 formally named species of Calaxius, including the present new species, ten are known from the Indo- West Pacific: C. acutirostris [East Africa, Madagascar and Australia, 219–504 m; record from the Philippines by Sakai and de Saint Laurent (1989) is questionable; cf. Poore & Collins (2009)], C. euophthalmus (known with certainty only from Indonesia, 397 m), C. izuensis (Japan, 440–465 m), C. manningi (Taiwan, 500 m), C. mimasensis (Japan, 133 m), C. poupini n. sp. (French Polynesia, 646–737 m), C ohsumiensis (Japan, 80–82 m), C. pailoloensis (Hawaii, 250 m), C. sibogae (known with certainty only from Indonesia, 397 m) and C. tungi (South China Sea, 367–402 m). Two species were described from the western Atlantic: Calaxius inaequalis (Puerto Rico, 289–309 m) and C. jenneri (North Caroline, 100 m). Calaxius galapagensis and C. kensleyi were described from the eastern Pacific (Galapagos Islands, 6 m) and eastern Atlantic (West Africa, 49.2–49.3 m), respectively. All but C. galapagensis occur in continental shelf depth to upper bathyal zone down to 737 m (Kensley & Hickman 2001; Komai et al. 2002; Clark et al. 2007; Poore & Collins 2009; Komai 2011; Sakai 2011; this study). The discovery of the present new species slightly extends the bathymetric range of the genus to 737 m. Although the geographic range of the genus is widely spread in tropical to subtropical areas in the world oceans, record of each species is rather limited. Vast majority of the 14 species is represented only by the respective type description and at most a few subsequent records, and thus real distributional range of each species remains still unknown.
Etymology. It is my pleasure to dedicate this new species to Dr. Joseph Poupin of Institut de Recherche de l’École Navale, Brest, in recognizing his many contributions to the taxonomy of decapod Crustacea, particularly of French Polynesia.
description: Published as part of Komai, Tomoyuki, 2016, Reappraisal of the two axiid genera Manaxius Kensley, 2003 and Calaxidium Sakai, 2014, and description of a new species of Calaxius Sakai & de Saint Laurent, 1989 from French Polynesia, Southwest Pacific (Crustacea: Decapoda: Axiidea), pp. 498-510 in Zootaxa 4098 (3) on pages 502-509, DOI: 10.11646/zootaxa.4098.3.4, http://zenodo.org/record/258557