Cycloachelous levigatus, Koch, 2021

Koch, Milan, 2021, Cycloachelous levigatus sp. nov., a new swimming crab (Crustacea: Decapoda Portunidae) from the South China Sea, Zootaxa 4970 (2), pp. 325-339 : 327-335

publication ID	https://doi.org/ 10.11646/zootaxa.4970.2.6
publication LSID	lsid:zoobank.org:pub:85BDD65D-7BAC-4357-8391-BF1ACAAAF23D
DOI	https://doi.org/10.5281/zenodo.4908118
persistent identifier	https://treatment.plazi.org/id/03C79A05-FFD6-FFC8-FF56-F9AEFC6B42B9
treatment provided by	Plazi
scientific name	Cycloachelous levigatus
status	sp. nov.

Treatment

Cycloachelous levigatus View in CoL , sp. nov.

All collected from Cuẩ Bé fishing port (12° 20‘ N, 109° 12‘ E), north off Nhatrang , Khanh Hoa Province, Vietnam GoogleMaps .

Holotype: 1♂ CW 23 mm, MNHN-IU-2014-10093, [GenBank n. MZ 127805 View Materials ], 27 Jun. 2012, fcn UO 12 Pa- Vn 12, coll. Z. Ďuriš, M. Koch

Allotype: 1♀ CW 15.2 mm, MNHN-IU-2014-10091, [GenBank n. MZ 127803 View Materials ], 30 Aug. 2013, fcn UO 60 G- Vn 13, coll. Z. Ďuriš, A. Šobáňová

Paratypes: 1♂ CW 18,2 mm, MNHN-IU-2014-10094, [GenBank n. MZ 127806 View Materials ] ; 1♂ CW 23.4 mm, MNHN-IU- 2014-10097 ; 1♀ CW 14.3 mm, MNHN-IU-2014-10092, [GenBank n. MZ 127804 View Materials ] ; 19♂♂ CW 14.4–21.7 mm , 2♀♀ CW 11.0, 11.5 mm, voucher n. MNHN-IU-10098, 27 Jun. 2012, fcn UO 12 Pa-Vn12, coll. Z. Ďuriš, M. Koch .

Other material: 4♂♂ CW 13.2–20.7 mm ; 2♀♀ CW 16.4, 18.0 mm, voucher n. MNHN-IU-10099, 26 Aug. 2013, fcn UO 46 G-Vn13, coll. Z. Ďuriš, A. Šobáňová. — 1♂ CW 20.6 mm, MNHN-IU-2014-10095, [GenBank n. MZ 127807 View Materials ]; 1♀ ov. CW 15.6 mm MNHN-IU-2014-10096, [GenBank n. MZ 127808 View Materials ]; 7♂♂ CW 12.8–23.3 mm, 3♀♀ CW 12.2–16.3 mm, voucher n. MNHN-IU-10100, 30 Aug. 2013, fcn UO 60 G-Vn13, coll. Z. Ďuriš, A. Šobáňová

Comparative material.

Cycloachelous orbitosinus : Syntypes, 2♂♂ CW 33.3, 33.3 mm, 2♀♀ CW 26.0, 29.2 mm, voucher n. USNM 41084, stn. B23, Mauritius, Cargados Carajos, 54.9 m, The Percy Sladen Trust Expedition, 31 Aug. 1905, H.M.S. Sealark, coll. S. J. Gardiner.

Other material, 1♂ CW 23 mm, MNHN-IU-2010-6278, [GenBank n. MZ 127809 View Materials ], stn CP3572, Southeast off Fort Dauphin, 25°11‘ S – 47°12‘ E, 75–77 m, Atimo Vatae Expedition, 8 May 2010, fishery vessel Nosy Be 11. (Photo http://coldb.mnhn.fr/catalognumber/mnhn/iu/2010-6278).— ♂ CW 31 mm, 2♀♀ CW 19.2, 19.5 mm, MNHN-IU- 2010-3271, stn CP3576, Cap Sainte Marie, 25°43.8‘ S –45|°18.8‘ E, 47 m, Atimo Vatae Expedition, 9 May 2010, fishery vessel Nosy Be 11.— 1♂ CW 25.3 mm, 1♀ CW 26.7 mm [ Fig. 2 View FIGURE 2 CD], MNHN-IU-2010-3290, stn CP3547, South off Cap Sainte Andavaka, 25°17‘58.2‘‘ S – 46°40‘18.5988‘‘ E, 69–70m, Atimo Vatae Expedition, 9 May 2010, fishery vessel Nosy Be 11.— 1♂ male, CW 27.9 mm, 2♀♀ CW 20.9, 23.8 mm, 1 intersex CW 22.8, MNHN-IU- 2018-4943, stn CP3575, Cap Sainte Marie, 25°41‘19.2012‘‘ S – 45°17‘9.5964‘‘ E, 45–48 m, Atimo Vatae Expedition, 5 May 2010, fishery vessel Nosy Be 11.— 3♂♂, CW 23.4–25.5 mm, 1♀ juv. CW 18.5 mm, MNHN-IU-2010-3146, stn CP3624, Southeast off Faux-Cap, 25°38.1‘ S – 45°57.0‘ E, 63 m, Atimo Vatae Expedition, 15 May 2010, fishery vessel Nosy Be 11.— 8♂♂, CW 25.0– 29.9 mm, 3♀♀ CW 21.0– 24.4 mm, 3♀♀ ov. CW 22.1–25.2 mm, MNHN-IU- 2018-4959/B.8877, stn. 22, Southeast off Sainte Anne Island, 5°16‘ S – 55°58‘ E, 60 m, ORSTOM-Reves2 Expedition, 6 Sep.1980.— 3♂♂, CW 29.8–35.7 mm, 3♀♀ CW 19.8–28.8 mm, MNHN-IU-2018-4960/B.8878, stn. 64, Southwest off Sainte Anne Island, 4°44‘ S – 55°22‘ E, 50 m, ORSTOM-Reves2 Expedition, 20 Sep. 1980.

Cycloachelous octodentatus : Holotype, 1♂ CW 21.7 mm, voucher n. NHM 1937.4.2., Siglap, Singapore, Jun. 1934, coll. Raffles Museum, det. Gordon 1938.

Description of C. levigatus sp. nov. holotype. Carapace ( Fig. 1B View FIGURE 1 ) almost hexagonal, CL/CW ratio 0.67. Front width 0.15 of CW, frontal region including inner orbital tooth 0.22 of CW, fronto-orbital width (measured between tips of outer orbital teeth) 0.57 of CW. Front subdivided into 4 teeth—median pair in length about one half of lateral; median sulcus between median teeth running ventrally to the spiniform projection not overreaching front, appressed to median epistomial tooth. Supraorbital margin smooth, with 1 well developed Y-shaped notch in middle, with tooth-like elevation near extraorbital angle. Inner orbital angle tooth-like, with glabrous ventromedial ledge. Infraorbital margin with distinct V-shaped lateral notch. Anterolateral margin armed by 9 teeth with granulated margins, first tooth larger with arched outer margin, second tooth distinctly smaller, teeth 3–8 subequal, sharp, projecting forwards, tooth 9 largest, about twice as long as penultimate, projecting laterally and forward. Posterolateral margin slightly granulate, almost straight, subequal in length with anterolateral margin; posterolateral angle rounded; posterior margin straight.

Carapace with dorsal surface densely covered by very short fine pila, regions well defined, elevated, demarcated by patches of distinct knob-like granules; protogastric patches of granules separated from mesogastric; mesobranchial granules subdivided into four patches; anterolateral region with 2 indistinct submarginal granular patches separated on the level of firth anterolateral teeth; epibranchial regions poorly defined with dispersed patches of granules; both cardiac and lateral postcardiac, median postcardiac regions each with simple patch of granules; additional oval patch of granules on each side of carapace between lateral postcardiac region and posterolateral margin.

All male thoracic sternites glabrous ( Fig 2B View FIGURE 2 ); sternites 3, 4 well separated; sternite 4 with distinct median groove, sternites 7, 8 fused medially, sulcus distinct on exposed outer half. Locking mechanism postero-medially on sternite 5 on sides of pleonal cavity; pair of short, bulbous, posteriorly directed lobes reaching about one quarter of sternite 6.

Pleon ( Fig. 2B View FIGURE 2 , 3D View FIGURE 3 ) ‘T’-shaped, with pleomeres 3–5 fused, with borders only very feebly demarcated by transverse shallow glabrous transversal sulci. Pleomeres 4–6 together with telson each smooth and glabrous. Sixth pleomere 0.8 times longer than wide, 1.6 times longer than telson, lateral margins rounded and forming obtuse angle. Telson narrowly triangular, 1.4 times longer than basal width, with rounded tip and slightly concave posterior margin. Pleomere 3 with high sharp convex laminar crest; lateral margins of crest only slightly concave, posterolateral angle rounded. Crest on pleomere 2 distinctly lower than on pleomere 3, posterior margin sinuate.

Basal antennal segment with deep groove on the part entering orbital cavity.

Third maxillipeds ( Fig. 3F View FIGURE 3 ) gently granulate on ischium, merus, exopod, with densely pilose margins; palp tapering distally, segments subcylindrical; merus slightly longer than broad, lateral, medial parts glabrous, anterolateral angle creating triangular lateral projection; ischium about 1.55 times merus length, with distinct longitudinal glabrous groove and row of granules on lateral margin. Exopod stout, about 0.4 of ischium width, with subdistal triangular projection on medial border; flagellum longer than merus width. Other mouthparts not dissected.

Chelipeds ( Fig. 1B View FIGURE 1 , 3E View FIGURE 3 ) symmetrical, relatively robust, length about 0.9 of maximum carapace width (incl. lateral teeth). Merus with 5 spines on anterior, 2 on posterior, borders, anterior one flattened. Carpus with 1 sharp inner spine, 1 flattened outer spine; one distinct carina on dorsal surface. Upper surface of palm with 2 granular crests, inner one ending by spine distally, outer surface with small spiniform tooth over articulation with carpus, with 2 granular crests ending on level of finger articulation, lower arched, creating outer ventral, sharply produced, margin; inner surface of palm with longitudinal granulate keel ending on the pollex tip and bearing very distinct sharp granules reaching half of the pollex; fingers straight, tapering distally, tips arched, 0.45 of maximum palm length, distinctly carinate. No molariform teeth present on cutting edge; fingers otherwise with some hardly defined groups tri- or tetralobed serial conical teeth.

Ambulatory leg 5 with merus gently serrate on posterodistal angle. Natatorial dactylus oval, 2.25 times longer than maximum width, elliptical, with longitudinal median groove; upper surface with two longitudinal glabrous paths. Propodus with 3 longitudinal glabrous paths on upper surface—2 anterior, 1 posterior marginal.

Male G1 ( Fig. 4A View FIGURE 4 ) long, slender; proximal part robust, biconvex, distinct proximolateral lobe trapezoidal, with serrate posterior half of lateral margin; distal part arched, tapering, with apex slender, not expanded.

Male paratypes. Morphologically identical with holotype, CL/CW ratio near to 0.7. Chelipeds with 5, rarely 4 or 6 anterior spiniform teeth on merus. Lateral margins of pleonal segment 6 occasionally more rounded.

Allotype. Selected female reaching 15.2 mm, CL/CW ratio 0.73. Shape of the carapace is consistent with that of males. Pleon ( Fig. 2E View FIGURE 2 ) broadly subtriangular, laterally convex, with the distinct transversal ridge on pleomere 4; pleomere 6 broadly rounded, semicircular; telson small, triangular, slightly longer than wide, with rounded tip. Chelipeds with the inner surface without roughly granulated longitudinal keel in contrast to males. Molariform teeth present on cutting edge or right chela; fingers with some hardly-defined groups tri- or tetralobed serial conical teeth. Vulvae ( Fig. 2F View FIGURE 2 ) located in the middle of pleonal sternites 6 on sides of pleonal cavity; gonopores forming narrow indistinct fissures with medial (inner) margin slightly convex and lateral (outer) margin straight.

Colouration. The general colour of the carapace and chelipeds is yellowish-brown with the red dark granules scattered evenly, defining more or less the regions of the carapace ( Fig. 5B View FIGURE 5 ); pollex with dark red granulate ridge on its ventral side. Sternites 4–8, and ventral surface of chelipeds and ambulatory legs pink. Posterior part of pleon with two pink stripes. Swimming legs with black tips and margins.

Etymology. Due to the character of the surface of sternites and pleon, the Latin word ‘ levigatus ’ (smooth) is proposed for the species name.

Remarks. Ward (1942) established genus Cycloachelous based on morphological characters: (1) carapace flat almost circular in outline (2) fronto-orbital margins more than half as wide as total CW (3) orbits with significant dorsal inclination and lower orbital margins clearly visible from a dorsal view (4) anterolateral angle of the merus of the external maxillipeds strongly produced or auriculate.

The actual number of representative species is for the genus is more or less unclear. Nguyen & Ng (2010) discussed the taxonomic position of the genus and its species composition where 9 taxa were chosen as its possible representatives. Two of them were separated into the new genus Cavoportunus Nguyen & Ng 2010 . Actually, the genus contains 6 species (2 subspecies): C. granulatus granulatus (H. Milne-Edwards, 1834) , C. granulatus unispinosus (Miers, 1884) , C. elongatus (A. Milne-Edwards, 1861) , C. octodentatus ( Gordon, 1938) , C. orbicularis ( Richters, 1880) , C. orbitosinus ( Rathbun, 1911) and C. suborbicularis ( Stephenson, 1975) .

Four species (two subspecies) are easily distinguishable from C. levigatus sp. nov.: C. granulatus unispinosus , with one tooth on the posterior border of the cheliped merus versus two teeth posteriorly on the cheliped merus in C. levigatus sp. nov., C. orbicularis and C. elongatus with circular shape of the carapace and with small ninth anterolateral teeth versus almost hexagonal carapace with double sized ninth anterolateral teeth in C. levigatus sp. nov. C. granulatus granulatus and C. suborbicularis with short, stout G1 with hook-like apex versus relatively slender and long in C. levigatus sp. nov.

The last two species— C. octodentatus and C. orbitosinus seem to be most relative to newly presented one. Examination of the photos of holotype C. octodentatus ( Fig. 6A–D View FIGURE 6 ) confirmed the presence of third and fourth fused anterolateral teeth and different shape of male G1, which is stouter and bent in the first distal third. This correspond well with the description and figures of Gordon (1938) and is significant for distinguishing of both species. The other morphological characters are almost identical with C. levigatus sp. nov.

Cycloachelous orbitosinus is morphologically very similar C. levigatus sp. nov., but there is a set of characters to distinguish both taxa: (1) thoracic sternites with distinct sulci ( Fig 2A View FIGURE 2 , 3A View FIGURE 3 ) versus glabrous thoracic sternites ( Fig. 2B View FIGURE 2 , 3D View FIGURE 3 ); (2) the male pleon with very distinct sulci on the surface of pleomeres 3–6 and with lateral margins of the sixth pleomere convex, anteriorly convergent ( Fig. 2A View FIGURE 2 , 3A View FIGURE 3 ), versus pleon with glabrous pleomeres, except of the indistinct sulcus on pleomere 3 and with lateral margins broadly angular ( Fig. 2B View FIGURE 2 , 3D View FIGURE 3 ); (3) female pleon with very distinct sulci on the surface of pleomeres 3–6 and with lateral margins of the pleomere 5 and 6 rounded/semicircular ( Fig. 2C View FIGURE 2 ), versus pleon with glabrous pleomeres, except of the sulcus on pleomere 3 and with lateral margins convex ( Fig. 2E View FIGURE 2 ); (4) third maxillipeds anterolateral triangular projection forming about one half ( Fig. 3B View FIGURE 3 ) versus one third of anterior margin ( Fig. 3E View FIGURE 3 ); (5) chela with the spine on upper surface directed obliquely upward ( Fig. 3C View FIGURE 3 ) versus forward direction ( Fig 3F View FIGURE 3 ); (6) inner surface of palm with indistinct granulate keel ( Fig. 1A View FIGURE 1 , 7 View FIGURE 7 AB), versus longitudinal granulate keel bearing very distinct sharp granules reaching half of the pollex ( Fig. 1B View FIGURE 1 ); (7) G1 distinctly arched with ventrally directed openings ( Fig. 4B View FIGURE 4 ), versus G1 slightly arched with opening directed forward ( Fig. 4A View FIGURE 4 ); (8) general colour of the carapace and chelipeds red ( Fig. 5A View FIGURE 5 ) versus yellowish-brown ( Fig. 5B View FIGURE 5 ). The molecular data support the presence of two well separated species (Fig. 9).

The actual distribution of C. levigatus sp. nov. is unclear, as previous records for C. orbitosinus might overlap with present new species. Only some of the previously published data provide details to match the presented new species by morphological (de Haan 1833; Stephenson & Rees 1967; Sakai 1939; Sakai 1976; Yamaguchi & Baba 1993) or molecular characters ( Spiridonov et al. 2014).

Gordon (1938: Fig 5g View FIGURE 5 ) and Stephenson & Rees (1967: figs. 6d, h) mentioned specimens from Philippines with long and slender G1 distinctly different in comparison with C. orbitosinus and C. levigatus sp. nov., which might indicate the presence of another closely related species.

Distribution. Nhatrang Bay, Vietnam —the type locality. A previous report from the same locality: Spiridonov et al. (2014). The other confirmed localities are Philippines ( Stephenson & Rees 1967) and Japan ( Sakai 1939; Sakai 1976). In comparison with C. orbitosinus reported from the western Indian Ocean— Mauritius, Madagascar, Seychelles ( Rathbun 1911; Gordon 1938; Crosnier 1962), Kenya, Socotra ( Spiridonov 1994) Somalia (Vannini, M. & Innocenti 2000) and Persian (Arabian) Gulf, Gulf of Aden ( Stephensen 1945; Apel & Spiridonov 1998; Naderloo 2017), it seems C. levigatus localities are in East or South-East Asia waters.