Tylopus khikheb Likhitrakarn, n. sp.
(Figs 7-9)
urn:lsid:zoobank.org:act: 891AC1DA-5662-430E-A530-82BCC718FE0C
TYPE MATERIAL. — Holotype. Laos • ♂; Vientiane Prefecture, Muang Fuang District, Ban Thoua Village, near Pha Thor Nor Kham; c. 250 m a.s.l.; 18°41’58”N, 102°07’58”E; 29.VI.2023; Sutcharit C. and Jeratthitikul E. leg.; CUMZ-PD0030.
Paratypes. Laos • 1 ♂, 3 ♀; same data as the holotype; CUMZ-PD0030 .
ETYMOLOGY. — “Khikheb” is a vernacular name commonly used in the northeastern regions of Thailand and in Laos to denote a flatbacked millipede ( Polydesmida); noun in apposition.
DIAGNOSIS. — Differs from all known congeners in showing almost missing to very poorly developed paraterga. This new species resembles T. hongkhraiensis Likhitrakarn, Golovatch & Panha, 2016, from northern Thailand, T. moniliformis Likhitrakarn, Golovatch & Panha, 2016, from southern Laos, and T. bokorensis Srisonchai & Likhitrakarn, 2023, from southern Cambodia, but it differs from both T. moniliformis and T. bokorensis by having a sternal cone between ♂ coxae 4 (Fig. 7I, J) (vs a lobe between each ♂ coxae 3 and 4); the distal part of the solenophore showing a constriction (Figs 8; 9) (vs being expanded or wide). Tylopus khikheb Likhitrakarn, n. sp. differs from T. hongkhraiensis by the postfemoral part of the gonopod showing neither process h nor z (Figs 8; 9) (vs with evident processes h and z).
DESCRIPTION
Measurements (n = 5; ♂, n = 2; ♀, n = 3). Length 16.3- 18.7 mm (♂), 18.5-21.3 mm (♀), width of midbody proand metazona 0.8-1.1 and 1.1-1.3 mm (♂) or 0.9-1.2 and 1.1-1.4 mm (♀), respectively.
Coloration of live animals dark brown (Fig. 7A) with lighter brown metaterga; legs light brown, venter and a few basal podomeres light brown to yellow-brown. Coloration in alcohol after three months of preservation faded to light brown; antennae and epiproct light yellow-brown to pallid, venter and a few basal podomeres light yellowish to pallid (Fig. 7 B-J).
Clypeolabral region and vertex sparsely setose, epicranial suture distinct. Antennae moderately long (Fig. 7A), extending past ring 3 (♂, ♀) when stretched dorsally. In width,> ring 3 <4 <collum <ring 2 <5 <6-17 <head (♂, ♀); body gently and gradually tapering on rings 18-20. Collum with three transverse rows of setae: 4+ 4 anterior, 2 + 2 intermediate and 3+ 3 posterior; a very faint marginal incision laterally in posterior 1/3; caudal corner very narrowly rounded, not drawn past rear tergal margin (Fig. 7 A-C).
Tegument smooth and shining, prozona very finely shagreened, metaterga almost smooth, delicately rugulose, leathery (Fig. 7 B-F, H). Postcollum metaterga with two transverse rows of setae: 2+ 2 anterior, always abraded, and 3+ 3 posterior, pattern traceable at least as insertion points. Tergal setae simple, slender, rather short, about 1/6 metatergal length. Axial line barely traceable on pro- and metazona (♂, ♀). Paraterga 2 well-developed (Fig. 7B, C), horizontal, anterior edges protruded anteriorly, fore corner bent ventrad, pointed; lateral edge with two minute incisions at about 1/3 paratergal length in front of posterior edge of parataterga; caudal corner very narrowly rounded (Fig. 7B). Paraterga 3 and 4 rounded and smooth, expanded laterally. Following paraterga virtually missing, on pore-bearing rings traceable only as small, rounded, laterally expanded bulges (♂) or small, rounded, laterally expanded bulges on all rings, larger on ♀ pore-bearing rings than in ♂.
Ozopores (Op) evident (Fig. 7C, E, H), lateral, each lying in an ovoid groove at about 1/3 metatergal length in front of posterior edge of metaterga.Transverse sulcus usually distinct (Fig. 7C, D, F), incomplete on ring 18, complete on rings 5-17 (♂, ♀), very narrow, not reaching the bases of paraterga, at most faintly beaded at bottom. Stricture between pro- and metazona wide, rather deep, beaded at bottom down to base of paraterga (Fig. 7 B-F, H). Pleurosternal carinae complete crests with a sharp caudal tooth on rings 2 and 3, reduced and remaining a sharp caudal tooth on ring 4, thereafter missing (♂, ♀) (Fig. 7C, E, H).
Epiproct (Fig. 7 F-H) rather short, flattened dorsoventrally, tip subtruncate, subapical lateral papillae small, but visible, lying close to tip. Hypoproct roundly subtrapeziform, small setigerous knobs at caudal edge well-separated (Fig. 7G).
Sterna sparsely setose, without modifications (Fig. 7G); an entire, high, inverted funnel-shaped, sternal lobe between ♂ coxae 4 (Fig. 7I, J). A paramedian pair of evident tubercles in front of gonopod aperture. Legs very long and slender, slightly thicker in ♂, midbody ones c. 1.3-1.5 (♂) or 1.2-1.4 times (♀) as long as body height, prefemora without modifications, ♂ tarsal brushes absent.
Gonopods very simple (Figs 8; 9); coxite (cx) slightly curved caudad and sparsely setose distoventrally. Prefemorite (pfe) densely setose, as usual, about 1/3 as long as femorite + “postfemoral” part. Fermorite (fe) straight and rather stout, slightly expanded distad, showing a distinct mesal groove, without outgrowths except for a low, sometimes poorly delimited lobe l; solenophore (sph) clearly coiled, flattened, suberect distally, devoid of processes.
REMARKS ON TYLOPUS SPECIES FROM LAOS
Tylopus nodulipes (Attems, 1953), the type species of Tylopus was originally reported from two localities: Luang Prabang Province, Laos and Mount Fan-Si-Pan, Lao Cai Province, Vietnam (Attems 1953). The male from Luang Prabang, Laos, was subsequently selected as the lectotype of this species (Likhitrakarn et al. 2014). Further records concerned Vietnam (Nguyen 2012), but none Laos.
Later, 11 further species of this genus were described from Laos (Likhitrakarn et al. 2016; Golovatch 2018). Finally, a new species, T. panhai, has recently been added (Srisonchai et al. 2023).
Consequently, a total of 15 species of Tylopus have been documented from Laos, including two new ones described above.
KEY TO SPECIES OF TYLOPUS JEEKEL, 1968 KNOWN TO OCCUR IN LAOS (BASED ON MALE CHARACTERS)
1. Body moniliform (Fig. 7 A-H). Paraterga present only on rings 2-4, thereafter missing ................................ 2
— Body not moniliform. Paraterga well-developed on most rings (Fig. 5 A-G) ................................................. 4
2. Both ♂ coxae 3 and 4 with sternal lobes ................. T. monoliformis Likhitrakarn, Golovatch & Panha, 2016
— A sternal lobe only between ♂ coxae 4 (Fig. 7I, J) ....................................................................................... 3
3. Body larger: length 16-21 mm. Colour pattern (Fig. 7A) on lighter metaterga. Gonopod process h absent (Figs 8; 9) ........................................................................................................ T. khikheb Likhitrakarn, n. sp.
— Body smaller: length ca 11 mm. Colour pattern with contrasting lighter paraterga, strictures between pro- and metazona, and insertion spots on metaterga. Gonopod process h present, as high as solenophore ................... ....................................................................................................................... T. longisetosus Golovatch, 2018
4. Collum and following metaterga densely and irregularly hairy. Sternal cones between ♂ coxae 4 isolated ....... ............................................................................................................................ T. hirsutus Golovatch, 2018
— Collum and following metaterga not do hairy. Sternal cones between ♂ coxae 4 fused basally into a single lamina ......................................................................................................................................................... 5
5. Metaterga roughly and conspicuously microgranulate ................................................................................. 6
— Metaterga not microgranulate, dull or smooth ............................................................................................ 9
6. Adenostyles present (Fig. 6E). Gonopod process x present (Fig. 6A, C, D) .................................................. 7
— Adenostyles absent. Gonopod process x absent ............................................................................................ 8
7. Coloration blackish, without a cingulate pattern. Tarsal brushes present until ♂ ring 8. Gonopod process z present, process h high, strongly twisted, tip clearly bifid ................................................................................ ................................................................................. T. thunghaihin Likhitrakarn, Golovatch & Panha, 2016
— Coloration brownish, with a dark cingulate pattern. Tarsal brushes present until ♂ ring 12. Gonopod process z absent, process h short, flattened, tip rounded (Fig. 6 A-D) .................... T. namnonensis Likhitrakarn, n. sp.
8. Midbody metaterga with two transverse rows of setae, 2+2 and 2+ 2 in each row, each seta borne on an evident tubercle or knob. Gonopod rather simple: only process h present ............ T. subtuberculatus Golovatch, 2018
— Midbody metaterga with two transverse rows of setae, 2+2 and 2+2 or 3+ 3 in each row, mostly traceable due to insertion points. Gonopod rather complex: processes h, z and r present ............ T. jaegeri Golovatch, 2018
9. Gonopod process m present ...................................................................................................................... 10
— Gonopod process m absent ....................................................................................................................... 12
10. Colour pattern with contrasting lighter posterior halves of collum and following metaterga and paraterga. Gonopod process m conspicuous, long; process z short without additional tooth, lower than half process h ............... 11
— Colour pattern with contrasting lighter paraterga and axial line on each metatergum. Gonopod process m small and short; process z long with a small, ventral, parabasal tooth, higher than process h .................................... .............................................................................................................................. T. beroni Golovatch, 2018
11. Gonopod telopodite more slender (slightly longer); process z an inconspicuous, very small lobe. Champasak Province, southwestern Laos ........................................................ T. panhai Srisonchai & Likhitrakarn, 2023
— Gonopod telopodite stout and thick, expanded distad; process z a conspicuous, rather long and spiniform lobe. Luang Prabang Province, northern Laos .............................................................. T. nodulipes (Attems, 1953)
12. Gonopod process z present ........................................................................................................................ 13
— Gonopod process z inconspicuous or absent ..................... T. retusus Likhitrakarn, Golovatch & Panha, 2016
13. Tarsal brushes present on legs of rings 2-6. Gonopod process x evident .......................................................... ........................................................................................ T. dorsalis Likhitrakarn, Golovatch & Panha, 2016
— Tarsal brushes absent or present until ring 18. Gonopod: process x absent ................................................ 14
14. Tarsal brushes present until ring 18. Gonopod process z evident, rather long and spiniform, longer than half process h ......................................................................................................... T. altmannae Golovatch, 2018
— Tarsal brushes absent. Gonopod process z very small or absent, shorter than one-third process h ................... .................................................................................. T. acuminatus Likhitrakarn, Golovatch & Panha, 2016