A remarkable new species of the millipede genus Trachyjulus Peters, 1864 (Diplopoda, Spirostreptida, Cambalopsidae) from Thailand, based both on morphological and molecular evidence Author Likhitrakarn, Natdanai Division of Plant Protection, Faculty of Agricultural Production, Maejo University, Chiang Mai 50290, Thailand Author Golovatch, Sergei I. Institute for Problems of Ecology and Evolution, Russian Academy of Sciences, Leninsky pr. 33, Moscow 119071, Russia Author Jeratthitikul, Ekgachai Animal Systematics and Molecular Ecology Laboratory, Department of Biology, Faculty of Science, Mahidol University, Bangkok 10400, Thailand Author Srisonchai, Ruttapon Department of Biology, Faculty of Science, Khon Kaen University, Khon Kaen, 40002 Thailand Author Sutcharit, Chirasak Animal Systematics Research Unit, Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand Author Panha, Somsak Animal Systematics Research Unit, Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand somsak.pan@chula.ac.th text ZooKeys 2020 925 55 72 http://dx.doi.org/10.3897/zookeys.925.49953 journal article http://dx.doi.org/10.3897/zookeys.925.49953 1313-2970-925-55 A531C6A9F7A84747B4DBA18D00237417 ABE5963FB9AD54E386C90D142708090D Trachyjulus magnus sp. nov. Figures 1 , 2 , 3 , 4 Type material. Holotype ♂ (CUMZ), Thailand, Surat Thani Province, Ban Na San District, Wat Tham Khrom Wanaram, 8°46'12.07"N , 99°22'6.36"E , 16.06.2018, leg. W. Siriwut, E. Jeratthitikul and N. Likhitrakarn. Paratypes. 15 ♂, 20 ♀ (CUMZ), 1 ♂, 1 ♀ (ZMUM), 1 ♂, 1 ♀ (NHMD), same locality, together with holotype. Name. To emphasize the largest body size of this species compared to all other species known in the genus. Diagnosis. This new species differs from all other Trachyjulus spp. by the largest body size (43.5-64.2 mm long, 2.1-2.8 mm wide), and also from the particularly similar and grossly sympatric T. unciger (23-42 mm long, 1.2-2.0 mm wide) in having the tegument of rings 2 and 3 nearly smooth (vs evidently carinate), carinotaxic formulae of typical rings (11-8/11-8+I/i+2/2+m/m vs 8-6/8-6+I/i+2/2+m/m), combined with the number of ommatidia (5-6+5-6 vs 4+4), and the posterior gonopods showing medial coxosternal processes ( mcp ) subtrapezoid (vs shorter and lobe-shaped). Description. Length of holotype ca 62.5 mm (Fig. 1A ) and that of paratypes 44.1-64.3 (♂) or 43.5-64.2 mm (♀); midbody rings round in cross-section (Fig. 2I ), their width (horizontal diameter) and height (vertical diameter) being similar; width of holotype 2.6 mm, of paratypes 2.1-2.7 (♂) or 2.1-2.8 mm (♀). Figure 1. Trachyjulus magnus sp. nov., habitus, live coloration. A ♂ holotype B paratypes. Scale bars: 1 cm. Coloration of live animals red-brown to yellow-brownish (Fig. 1 ), venter and legs brownish yellow to yellowish, antennae light to pale yellowish, eyes blackish, a thin axial line traceable; coloration in alcohol, after one year of preservation, similar, but body yellow-brownish to light brownish, vertex red-brown to light brown, eyes blackish to brownish. Body with 80p+2a+T rings (holotype); paratypes with 68-86p+1-3a+T (♂) or 69-93p+1-4a+T (♀) rings. Eyes large, flat, ovoid, with 6(5)+6(5) ommatidia arranged in a single vertical row (Fig. 2D ). Antennae short and clavate (Figs 2A, B, D, F , 5A ), extending past ring 4 laterally (♂, ♀), with four evident apical cones (Fig. 2G ), antennomeres 5 and 6 each with a small distoventral group or corolla of bacilliform sensilla (Figs 2F, H , 5A ). Clypeus with five teeth anteromedially (Fig. 2E ). Gnathochilarium oligotrichous, mentum single (Figs 2E , 4B ). In width, head = ring 2 <ring 4 = 5 <3 <6 <7 <8 <9 <10 <collum = midbody ring (close to 12th to 14th); body abruptly tapering towards telson on a few posteriormost rings (Fig. 2B, O ). Postcollar constriction evident, but not particularly strong (Fig. 2B ). Collum (Fig. 2A-C ) smooth, only near lateral edges with 2-4 light, short, superficial striae (Fig. 2A-C ). Rings 2 and 3 nearly smooth, with 6-9 light, superficial striae (Fig. 2A, B ). Following metaterga clearly and rather strongly carinate (Fig. 2A, B, N, O ), especially so from ring 5 on, whence porosteles commence, these being completely absent from legless rings where ozopores are missing (Fig. 2A ). Porosteles large, but low, conical, round, directed caudolaterad, broader than high (Fig. 2L ). Carinotaxic formula of metaterga 4, 10-11/10-11+m/m (Fig. 2A, B ). Carinotaxic formulae of following rings typically 11-8/11-8+I/i+2/2+m/m (Fig. 2A, B, N, O ); all crests and tubercles, including porosteles, low. Tegument smooth (Figs 1 , 2A, B, N, O ), shining throughout. Fine longitudinal striations in front of stricture between pro- and metazonae, remaining surface of prozonae very delicately shagreened (Fig. 2A, B, M-O ). Metatergal setae absent. Rings 2 and 3 each with long pleural flaps. Midbody ring nearly round in cross-section (Fig. 2I ). Epiproct (Fig. 2N-P ) simple, bare, smooth, regularly rounded caudally. Paraprocts smooth, regularly convex and densely setose (Fig. 2P ). Hypoproct as usual, transversely bean-shaped, slightly concave caudally (Fig. 2P ). Ventral flaps behind gonopod aperture on ♂ ring 7 barely distinguishable as low swellings, forming no marked transverse ridge. Legs short, on midbody rings about 2/3 (♂, ♀) as long as body height (Figs 2I, J ). Claw at base with a strong accessory spiniform claw almost half as long as main claw (Fig. 2K ). Tarsi and tarsal setae very delicately fringed. Figure 2. Trachyjulus magnus sp. nov., A-C, I-P ♀ paratype, D-H ♂ paratype. A, B anterior part of body, lateral and dorsal views, respectively C collum, dorsal view D cephalic capsule, dorsal view E gnathochilarium, ventral view F antenna, lateral view G tip of antenna H bacilliform sensilla on antennomere 5, lateral view I cross-section of midbody ring J midbody rings, ventral view K claw of midbody leg L enlarged ozopore region, lateral view M midbody prozona, dorsal view N-P posterior part of body, lateral, dorsal and ventral views, respectively. ♂ legs 1 highly characteristic (Figs 3A, B , 4C, D ), with a strongly enlarged, long, slim, central hook (actually a pair of very tightly adjacent) curved forward (Figs 3B, C , 4C ), and strong, high, densely setose, triangular, 1-ringed telopodites (Figs 3A, B , 4E, F ). ♂ legs 2 (Figs 3C, D , 4E, F ) slightly enlarged, with high and large coxae; telopodites hirsute on anterior face; penes subconical, rounded apically, fused at base, bare. ♂ legs 3 (Figs 3E , 4H ) slightly reduced, modified in having coxae especially slender and elongate. Anterior gonopods rather simple (Figs 3F-H , 4I, J ), with 1 or 2 strong apical setae on subtrapezoid, medial, coxosternal processes ( mcp ); telopodites ( te ) club-shaped, curved, sparsely setose, nearly as high as lateral coxosternal process ( lcp ), the latter slender and long, placed basal to telopodites. Anterior parts of lateral coxal processes and telopodites rod-shaped, slender and digitiform, with apicolaterally denticulate tips (Fig. 3H ). Posterior gonopods (Figs 3I-L , 4K, L ) highly compact, coxites well separated from sternum, fused only basally, with a parabasal field of coniform microsetae caudally, each with a setose, paramedian, coxal process ( pp ) (Figs 3I , 4L ); telopodites ( te ) high, distally microserrate/papillate (Fig. 3K, L ); anterior coxal processes ( ap ) elongate, shorter than telopodites, densely setose and rounded distally (Figs 3I-K , 4K, L ); both divided by a very high, axe-shaped flagellum ( f ) (Figs 3I, J , 4K, L ). Remark. The often striking colour difference between head+collum+ring 2 and the remaining rings observed in SEM micrographs (Fig. 2 ) is certainly an artifact resulting from unwanted electrical charging. Figure 3. Trachyjulus magnus sp. nov., ♂ paratype. A, B Legs 1, frontal and caudal views, respectively C legs 2, caudal view D penes, caudal view E legs 3, frontal view F, G anterior gonopods, caudal and frontal views, respectively H telopodite tips of anterior gonopods I, J posterior gonopods, caudal and frontal views, respectively K, L telopodite tips of anterior gonopods, caudal and frontal views, respectively. Figure 4. Trachyjulus magnus sp. nov., ♂ holotype. A Antenna, lateral view B gnathochilarium, ventral view C, D legs 1, caudal and frontal view, respectively E, F legs 2, caudal and frontal view, respectively G midbody leg, frontal view H legs 3, frontal view I, J anterior gonopods, frontal and caudal views, respectively K, L posterior gonopods, frontal and caudal views, respectively. Scale bars: 0.2 mm.