Plusioglyphiulus digitiformis, Likhitrakarn, Natdanai, Golovatch, Sergei I., Srisonchai, Ruttapon, Franck Brehier,, Lin, Aung, Sutcharit, Chirasak & Panha, Somsak, 2018

Likhitrakarn, Natdanai, Golovatch, Sergei I., Srisonchai, Ruttapon, Franck Brehier,, Lin, Aung, Sutcharit, Chirasak & Panha, Somsak, 2018, Two new species of the millipede family Cambalopsidae from Myanmar (Diplopoda, Spirostreptida), ZooKeys 760, pp. 55-71 : 55

Plusioglyphiulus digitiformis sp. n. Figs 1, 2, 3, 4

Holotype

♂ (CUMZ), Myanmar, Shan State, Taunggyi, Hopong, Parpant area, cave, 20°43'30"N, 97°08'04"E, 23.09.2015, leg. C. Sutcharit and R. Srisonchai.

Paratypes.

7 ♂, 18 ♀ (CUMZ), same data as holotype. 2 ♂, 1 ♀ (MNHN, MY15-16/09), Shan State, Jatwet Gu (Linwe Depression Cave #2), limestone, 21°13'40"N, 96°33'24"E, 29.11.2015; 1 ♀ (MNHN, MY15-17/10 (SS06)), same State, Kyauk Khaung Cave (Stone Cave), limestone, 21°11'28"N, 96°33'09"E, 29.11.2015; 9 ♂, 17 ♀, 1 juv. (MNHN, MY15-18/06), same State, Mondawa Gu Cave, limestone, 20°45'17"N, 97°01'03"E, 01.12.2015; 7 ♀ (MNHN, SS11), same locality, 21.09.2015; 13 ♂, 15 ♀ (MNHN, MY15-20/04), same State, Parpent Cave n°1, Guano, limestone, 20°51'03"N, 97°14'23"E, 02.12.2015; 2 ♂, 3 ♀, 4 juv. (MNHN, SS15), same locality, 23.09.2015; 6 ♂, 17 ♀ (MNHN, MY15-21/07), same State, Parpent Cave n°2, Guano, limestone, 20°51'04"N, 97°14'28"E, 02.12.2015, all leg. F. Bréhier.

Other material.

4 ♂, 14 ♀ (MNHN, MY15-14/09), 2 ♂, 3 ♀ (ZMUM), Mon State, Saddan Sin Gu Cave, limestone, tower karst, 16°31'43"N, 97°43'02"E, 26.11.2015; 1 juv. (MNHN, MY15-15/07), same State, Nathack Gu Cave (Two Level Cave), limestone, tower karst, 16°31'33.5"N, 97°42'48.8"E, 26.11.2015, all leg. F. Bréhier.

Etymology.

To emphasize the finger-shaped apicomesal coxoternal processes (acp) of the anterior gonopodal coxosternum; adjective.

Diagnosis.

This new species is apparently most similar to P. antiquior Golovatch, Geoffroy, Mauriès & VandenSpiegel, 2011, from a cave in Kanchanaburi Province, Thailand ( Golovatch et al. 2011), in sharing the special the carinotaxic formulae of the collum and postcollum rings (Fig. 2 A–C, H, I, N, O), ♂ legs 1 with a short central hook (Figs 3A, B, 4C), ♂ legs 2 with modestly enlarged telopodites (Figs 3D, 4D), coupled with the simple plate-like anterior gonopods (Figs 3G, H, 4G), the complex posterior gonopods in which the coxites are densely setose paramedially and each supplied with an evident fovea, and the telopodites are evident and digitiform (Figs 3K, L, 4H, I). However, the new species differs from P. antiquior in the more clearly divided crests on metaterga, the lateral ones being somewhat higher, coupled with the 3-segmented telopodites of ♂ legs 1, the anterior gonopodal coxosternum showing higher and nearly straight apicomesal coxoternal processes (acp) and very evident basolateral coxosternal processes (bcp), as well as the higher and acuminate anterior coxal processes (ap) of the posterior gonopods, the latter’s telopodite (te) demonstrating an apical fovea that bears a group of microsetae at the bottom (Figs 3K, L, 4H, I).

Description.

Length of holotype ca. 18 mm; adult paratypes 12-27 (♂) or 13-29 mm (♀); midbody segments circular in cross-section (Fig. 2K), width in holotype 0.9 mm; paratypes 0.8-1.0 (♂, ♀).

Colouration of live animals light red-brown (Fig. 1) with lighter anterior and posterior parts of body; antennae, venter and legs light yellowish; coloration in alcohol, after two years of preservation, uniformly light red brownish to dark castaneous brown, dorsal crests and porosteles usually dark brownish. Antennae and venter yellow brownish to brownish. Ommatidia brown to blackish.

Adult body with 46p+3a+T (holotype); paratypes with 37 –60p+1– 4a+T (♂) or 36 –66p+1– 4a+T (♀). Eye patches transversely ovoid, with 3+(1-2) blackish, rather flat ommatidia in 1-2 longitudinal rows. Antennae short and clavate (Figs 1, 2A, 2B, 2D, 2E, 4A), extending behind ring 4 laterally, antennomeres 5 and 6 each with a small apicodorsal field or corolla of bacilliform sensilla (Figs 2E, 4A). Gnathochilarium oligotrichous, each lamella lingualis with 3-4 setae; mentum undivided (Fig. 4B).

In width, collum = midbody rings (close to 13th to 15th)> head = ring 4> 10> 9> 8> 7> 6> 4 = 5> 2> 3; body abruptly tapering towards telson on a few posteriormost rings (Fig. 2 N–P). Postcollar constriction evident due to only a moderately enlarged collum (Fig. 2B, C).

Collum with 6+6 longitudinal crests starting from anterior edge, carinotaxic formula of collum, 1+2p+3+4p/t+5p/t+pp+/ma (Fig. 2 A–C).

Following metaterga similarly strongly crested (Figs 1, 2 A–C, H, I, L, N, O), especially so from ring 5 onwards, whence porosteles commence, these tubercles clearly reduced on legless segments where ozopores are missing (Fig. 2N). Porosteles large, high, conical, round, directed caudolaterad, wider than high (Fig. 2J); ozoporiferous crests distinctly divided into two about midway, their anterior halves being higher (Fig. 2A, B, C, H, I, L, N, O). Carinotaxic formulae of metaterga 2-4, 2+2/2+M+2/2+2 (Fig. 2A, B); usual formula of following metaterga, 2/2+I/i+3/3+I/i+2/2 (Fig. 2A, B, H, I, L, N, O); all crests and tubercles low.

Tegument delicately alveolate-areolate (Fig. 2B, H, I, L, M, N, O), dull throughout. Fine longitudinal striations in front of stricture between pro- and metazonae, remaining surface of prozonae very delicately shagreened (Fig. 2F, L). Metatergal setae absent. Segments 2 and 3 each with long pleural flaps.

Limbus extremely finely and more or less regularly denticulate.

Epiproct (Fig. 2 N–P) broadly rounded apically, with 1+1 paramedian tubercles at midway. Paraprocts rather clearly flattened, each with a faint premarginal sulcus medially (Fig. 2P). Hypoproct emarginated at caudal margin (Fig. 2P)

Ventral flaps behind gonopod aperture on ♂ segment 7 barely distinguishable as low swellings, forming no marked transverse ridge.

Legs nearly as long as body diameter (Fig. 2K), claw at base with a strong accessory claw almost half as long as claw itself (Fig. 4F).

♂ legs 1 with an unusually short, central hook and relatively strongly reduced, 3-segmented telopodites (Figs 3A, B, 4C), each with a small and sharp claw (Fig. 3C).

♂ legs 2 clearly enlarged, with high and large coxae; telopodites hirsute on anterior face; penes broad, oblong-subtrapeziform, fused at base, each with 3-4 strong setae distolaterally (Figs 3D, 4D).

♂ legs 3 modified in having coxae especially slender and elongate, but with somewhat shortened telopodites (Figs 3E, F, 4E).

Anterior gonopods (Figs 3 G–I, 4G) with a typical shield-like coxosternum, the latter modestly setose on caudal face and provided with a concave notch separating a pair of high, nearly straight, terminally rounded, apicomesal, coxosternal processes (acp) and a much lower basolateral coxosternal processes (bcp), these being rounded at tip; telopodite (te) typical, rather stout, movable, 1-segmented, lateral in position, with several strong apical setae and a field of small microsetae at base, slightly longer than adjacent bcp.

Posterior gonopods (Figs 3 J–M, 4H, I) highly compact, contiguous basally until about midheight; each with a densely setose paramedian coxal process (pp) (Fig. 3M) and with two higher central pieces: anterior coxal process (ap) elongate, distally represented by an acuminate lamina; caudal coxal process (cp) subtriangular, membranous, rounded at tip; each telopodite (te) vase-shaped, with a compact group of coniform microsetae placed at bottom of an apical fovea (Fig. 3J), with another, parabasal field of microsetae on anterior face (Figs 3L, 4H, I).

Remarks.

The genus Plusioglyphiulus Silvestri, 1923 has recently been reviewed ( Golovatch et al. 2009, 2011) and shown to comprise 27 species ranging from northern Thailand and Laos in the west to Borneo in the east and southeast. This new species is the first Plusioglyphiulus to be recorded from Myanmar. Based on the pigmented body and eye patches, and like most if not all other cave-dwelling congeners known to date, P. digitiformis sp. n. seems to be hardly more than a troglophile.

Most species of this genus show particularly enlarged colla with the tergal crests both on the collum and following segments being clearly divided transversely into three parts. Only two species, P. antiquior and P. panhai Golovatch, Geoffroy, Mauriès & VandenSpiegel, 2011, both from caves in Thailand and both found quite close to the frontier to Myanmar, are remarkable in still showing the pattern of carinotaxy observed in the genus Glyphiulus Gervais, 1847 ( Golovatch et al. 2011).

In particular, while their gonopods are relatively complex and unequivocally the same as in typical Plusioglyphiulus , the carinotaxic pattern is simple and typical of Glyphiulus , i.e., the crests on their colla and following metaterga are divided transversely into two, not three, parts. In this respect, P. digitiformis sp. n. clearly joins the above duet, showing the closest similarities, both morphologically and geographically, to P. antiquior .

Non-type material shows all characters of the type series, but their localities lie very far from the others (ca. 470 km) (Fig. 8). We hope that future molecular studies will answer the question of the conspecificity (or not) of all above populations.

Interestingly, the famous Burmese amber, 99-100 Mya, appears to contain a typical Plusioglyphiulus yet to be described (Wesener in litt.). This is evidence both of the very old age of this genus and its long presence in situ.