Cyclodius taiwanensis, Hsueh & Tzeng, 2024

Genus Cyclodius Dana, 1851 View in CoL

Cyclodius taiwanensis sp. nov. ( Figs. 4A–H View Fig , 5A–D View Fig , 6A–D View Fig , 7A–F View Fig ) urn:lsid:zoobank.org:act:9BC4D0FC-A342-413D-98EF-FA819C794785

Material examined: Holotype, NMNS 8772-18 View Materials , ò, 8.9 × 6.2, Jihuei , Taitung County, 9 October 2010 . Paratypes: 1 ñ, NMNS 8772-19, 6.6 × 4.2, Wanlitong, Pingtung County, 13 November 2009; 1 ò, NMNS 8772-20, 4.8 × 3.3, Jihuei, Taitung County, 7 October 2010; 1 ñ, NMNS 8772-21, 4.3 × 2.7, Jihuei, Taitung County, 27 September 2014; 1 ò 1 ñ, NMNS 8772- 22–23, 7.2–9.6 × 4.6–6.2, Jihuei, Taitung County, 28 April 2017.

Etymology: The name is derived from Taiwan, the island where the specimens were collected.

Description: Holotype, carapace ( Figs. 4A, B View Fig , 6A, B View Fig ) transversely hexagonal, width about 1.44 length; dorsal surface granulate, covered with long and short simple light-colored setae; regions weakly defined. Front moderately convex, about 0.27 times carapace width, strongly deflexed ventrally, margin granulate; divided into two lobes by wide V-shaped notch, continuing posteriorly as shallow median groove on dorsal carapace. Anterolateral margin with anterolateral direct spinose teeth, separated by concave gaps; tooth 1 with 2 emergent spines, larger than supraorbital tooth, tooth 2 and 3 subequal in size, both with 2 large and 1 small anterolateral pointed spine, tooth 4 with 1 large spine and secondary spines. Posterolateral margin longer than anterolateral margin, slightly convex medially.

Orbits ( Figs. 4A–C View Fig , 6A, B View Fig ) suboval, margins denticulate, supraorbital margin with 2 small notches medially; inner pre-frontal supraorbital and exorbital tooth weakly developed. Eyes well developed, eyestalks short, stout, corneas large. Antennular fossae transversely oval; antennules folding transversely. Basal antennal article with small lateral flange, entering less than halfway into orbital hiatus. Antennae freely entering orbital hiatus.

Third maxillipeds ( Figs. 4C, D View Fig , 7A View Fig ) subrectangular, length to width ratio about 1.55; palp tapering distally, articles subcylindrical; merus subquadrate, length to width ratio about 0.55, anterolateral angle concave, anterior margin sinuous and granulate, few stout and simple setae; external surface with scattered granules; ischium subrectangular, about 2.58 times longer than merus, sulcate submedially, mesial margin cristate, serrated, lined with submarginal setae; exopod stout, external margin straight, internal margin denticulate, tapering slightly toward distal end, distal end concave.

Thoracic sternum ( Figs. 4G View Fig , 7B View Fig ) margins cristate; sternites 1, 2 fused with low of transverse granules on suture; sternites 2, 3 separated by narrow, deep suture, margins smooth; sternites 3, 4 mostly fused, with remnants of suture only at lateral edges; sternite 4 with prominent median longitudinal line extending through entire exposed length, lateral margins slightly convex; sutures 4/5, 5/6 joining toward median longitudinal axis of thoracic sternum; small, central, triangular, non-calcified area present between sternites 6, 7 within sternopleonal cavity; press-button on anterior half of sternite 5.

Chelipeds ( Figs. 4E, F View Fig , 6C View Fig ) subequal, moderately robust, external surfaces granulate covered with long and short simple, light-colored setae. Meri moderate long, distal end extending slightly beyond carapace anterolateral margin in dorsal view, upper margin unarmed, lower margin denticulate. Carpi rhombicshaped, covered with rows of granules. Palm external surface covered with row of granules. Fingers thick, tips hemi-cupuliform, pigmentation restricted to fingers; dactylus gently curved toward distal end, dorsal margin with 2 rows of granules proximally, 3 large teeth on cutting edge; pollex straight proximally, slightly curved upward distally, 3 or 4 large teeth on cutting edge.

Ambulatory legs ( Figs. 4A, H View Fig , 6D View Fig ) flattened, broad, moderate in length, P3, P4 longest, P5 shortest; surfaces entirely granulate, covered with long and short simple, light-colored setae; anterior margin of meri, carpi, propodi, dactyli denticulate; posterior margin of meri, propodi, dactyli denticulate; dactyli single-tipped. P5 merus subrectangular, median length about 1.86 times greatest width; carpus curved, distal end distinctly wider than proximal end, median length about 1.11 times greatest width; propodus subrectangular, median length about 0.91 times greatest width; dactylus longer than propodus, stout proximally, tapering distally, terminating in robust, short chitinous claw with length 1.43 times greatest width.

Pleon ( Figs. 4G View Fig , 7C View Fig ) moderate long relative to thoracic sternum, tip of telson reaching level slightly lower to sternal condyles of P1 coxae; somite 1 trapezoidal with anterior margin strongly concave, somite 2 trapezoidal, as wide as somite 1 with anterior margin strongly concave and posterior margin strongly convex; somites 3–5 fused with residue sutures reaching 1/3 to median line, base of somite 3 widest, distal somites progressively narrower, combined lateral margin gently concave; somite 6 subquadrate, width about 1.56 times length, anterior margin slightly concave, lateral margins and posterior slightly sinuous; telson subtriangular, angles round, basal width about 1.71 times median length.

G1 ( Figs. 5A, B View Fig , 7D–F View Fig ) moderate in length, stout, distal half acutely bent lateroventrally with 5 long and 6–8 short, simple, subdistal setae, numerous short spines; distal tip lobe ovate with round-tipped. G2 sigmoidal in shape, about one-third length of G1.

Female morphology: The immature female ( Figs. 5C, D View Fig , 7G View Fig ) is morphologically similar to the male in most body parts, except for the sexual characteristics. The pleon of the female is generally wider and more elongate-oval in shape compared to that of the male. The vulvae are oval, lack an operculum, and are located on the mesial fourth of sternite 5.

Distribution: Known only from type locality and Wanlitong, Pingtung County.

Remarks: The genus Cyclodius Dana, 1851 was synonymized as a junior name of Phymodius by A. Milne-Edwards (1863) but was resurrected by Davie (2002) and had been used since ( Lasley et al. 2015: 173). The current recognized species within the genus include: Cyclodius drachi (Guinot, 1964) , Cyc. granulatus (Targioni-Tozzetti, 1877) , Cyc. granulosus de Man, 1888 ; Cyc. nitidus (Dana, 1852) , Cyc. obscurus (Hombron and Jacquinot, 1846) , Cyc. paumotensis ( Rathbun, 1907) , Cyc. perlatus (Nobili, 1905) , and Cyc. ungulatus (H. Milne Edwards, 1834) ( Lasley et al. 2015: 173) . The present study introduces a new member to the genus.

The present species exhibits a basal antennal article ( Figs. 4C View Fig , 6B View Fig ) similar to that of Cyclodius Dana, 1851 , where the basal antennal article has a distolateral extension occluding less than half the length of the orbital hiatus ( Serène 1984: 233; Ng and Yang 1998: 1693, fig. 5B; Clark and Ng 1999: 354, 359, fig. 6C, tabl. 1; Lai et al. 2011: 433; Lasley et al. 2015: 173, fig. S5B, D). Among known Cyclodius species, only Cyc. paumotensis ( Rathbun, 1907) shares the characteristic of having the carapace and external surfaces of chelipeds covered in long and short simple, light-colored setae ( Figs. 4A, B. E, F View Fig , 5C View Fig ; Serène 1984: 233; Clark and Galil 1993: 1143, figs. 35B, 43A; Lasley et al. 2015: 173, fig. S1C). However, Cyc. taiwanensis sp. nov. can be distinguished from Cyc. paumotensis by: 1) weakly defined carapace regions (versus well-defined) ( Figs. 4A, B View Fig , 5C View Fig ; Serène 1984: 241, pl. XXXIII D; Clark and Galil 1993: 1145, fig. 35B; Lasley et al. 2015: 173, fig. S1C); 2) an anterolateral margin without apical or accessary spines (versus with apical or accessory spines) ( Figs. 4A, B View Fig , 5C View Fig ; Serène 1984: 241, fig. 143d; Clark and Galil 1993: 1145, fig. 10A, 35B; Lasley et al. 2015: 173, fig. S1C); 3) a greater basal width to median length ratio of the 6 th somite and telson (1.63 and 1.80 versus 1.34 and 1.34, respectively) ( Figs. 4G View Fig , 7C View Fig ; cf. Rathbun 1907: 52, pl. 2b); and 4) the G1 acutely bent subdistally with a round-tipped distal lobe (versus gently curved subdistally with a sharp distal lobe) ( Figs. 5A, B View Fig , 7D–F View Fig ; Serène 1984: 241, fig. 145; Clark and Galil 1993: 1143, fig. 10D–G; Lasley et al. 2015: 173, fig. S3B).

The G1 structure is considered a reliable distinguishing characteristic among Cyclodius species ( Lasley et al. 2015: 173). Although the G1 form in Cyc. taiwanensis sp. nov. is unique within the genus, it shows some resemblance to that of Pilodius luomi Serène, 1971 (= Pilodius miersi (Ward, 1936)) , as described by Serène (1971: 914–914) ( Figs. 5A, B View Fig , 7D–F View Fig ; Serène and Van Luom 1959: 307, fig. 2E, F; Serène 1971: 58; Serène 1984: 245, figs. 153–158; Clark and Galil 1993: 1136–1137; Lasley et al. 2023: 6, fig. 2). Both species exhibit a G1 with a round-tipped distal lobe; however, Cyc. taiwanensis sp. nov. has a subdistally acutely bent G1, an apical area without short spines, and few long, simple setae subapically; whereas P. luomi has a G1 that gently curves subdistally, with an apical area featuring many short spines and numerous long, simple setae ( Figs. 5A, B View Fig , 7D–F View Fig ; Serène and Van Luom 1959: 307, fig. 2E, F).

Cyclodius taiwanensis sp. nov. can be further distinguished from P. luomi View in CoL by: 1) weakly defined carapace regions (versus well-defined) ( Figs. 4A, B View Fig , 5C View Fig ; Serène and Van Luom 1959: 307, pl. 1D); 2) an anterolateral margin without apical or accessary spines (versus with spines) ( Figs. 4A, B View Fig , 5C View Fig ; Serène and Van Luom 1959: 307, pl. 1D); 3) dark pigmentation of fingers not expanding onto the palm (versus expanding onto the palm) ( Figs. 4A, E, F View Fig , 6C View Fig ; Serène and Van Luom 1959: 307, pl. 1D); and 4) the 6th somite of the male pleon having nearly equal proximal and distal margins length (versus a longer distal margin) ( Figs. 4A, E, F View Fig , 6C View Fig ; Serène and Van Luom 1959: 307, fig. 2A).

Similarly, Cy c. taiwanensis sp. nov. differs from P. miersi View in CoL in these traits: 1) weakly defined carapace regions (versus well-defined) ( Figs. 4A, B View Fig , 5C View Fig ; Clark and Galil 1993: 1137, fig. 34A); 2) a deep, V-shaped notch between the frontal lobes (versus a U-shaped indentation) ( Figs. 4A, B View Fig , 5C View Fig ; Clark and Galil 1993: 1137, figs. 7A, 34A); 3) an anterolateral margin without spines (versus with spines) ( Figs. 4A, B View Fig , 5C View Fig ; Serène and Van Luom 1958: 93: 307; Clark and Galil 1993: 1137, figs. 7B, 34A); 4) dark pigmentation of fingers not expanding onto the palm (versus expanding) ( Figs. 4A, E, F View Fig , 6C View Fig ; Serène and Van Luom 1958: 93; Clark and Galil 1993: 1137, fig. 34A); 5) ambulatory legs lacking dactyl-propodal locks (versus present) ( Figs. 4H View Fig , 6D View Fig ; Clark and Galil 1993: 1137, fig. 7C); and 6) a G1 subdistally bent acutely, with an apical area without short spines and few subapical setae (versus gently curving subdistally, with an apical area containing many short spines and numerous subapical setae) ( Figs. 5A, B View Fig , 7D–F View Fig ; Clark and Galil 1993: 1137, fig. 7D–F).