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Research Article
Occurrence of the millipede genus Tonkinosoma Jeekel, 1953 in China, with the description of the first presumed troglobitic species of this genus (Diplopoda, Polydesmida, Paradoxosomatidae)
expand article infoWeixin Liu, Sergei Golovatch§
‡ Agricultural University,, Guangzhou, Guangdong Province, China
§ Russian Academy of Sciences, Moscow, Russia
Open Access

Abstract

The genus Tonkinosoma Jeekel, 1953 has hitherto been known to contain only two species, both from northern Vietnam. T. flexipes Jeekel, 1953, the type species of the genus, is recorded from Guangxi, southern China, for the first time. T. tiani sp. n., a presumed troglobite, is described from caves in Guizhou, southwestern China. A key is presented to all three species of the genus.

Keywords

Guangxi, Guizhou, key, new record, new species, Tonkinosoma , troglobite

Introduction

The millipede genus Tonkinosoma Jeekel, 1953 was originally proposed to encompass only a single species, T. flexipes Jeekel, 1953, from northern Vietnam (Jeekel 1953). The tribe Tonkinosomatini Jeekel, 1968 was erected to comprise not only Tonkinosoma, but also a few other genera (Jeekel 1968). However, this tribe has since been merged first with Sulciferini Attems, 1898 (cf. Golovatch 2014) and, later, with Chamberliniini Wang, 1956 (cf. Golovatch 2015a). Nguyen (2011), when reviewing Tonkinosomatini in the scope of the fauna of Vietnam, described a second species from northern Vietnam: T. jeekeli Nguyen, 2011.

At present, Tonkinosoma can be diagnosed as a genus of the Himalayan and southeast Asian tribe Chamberliniini characterized by the gonopods which show a postfemoral part demarcated basally by an indistinct (T. flexipes) or distinct (T. jeekeli) geniculation cingulum and distally at least by a lateral sulcus. Unlike the other contribal genera, the femorite is long and slender and, like the postfemoral part, it is devoid of outgrowths, the seminal groove runs all along the mesal face of the femorite, the solenomere is long and flagelliform, and the solenophore is a long, hyaline, folded lobe that shows a lamina medialis and a lamina lateralis, both sheathing the solenomere. As in most Chamberliniini, both solenomere and solenophore are usually subcircular (Chen et al. 2010; Nguyen and Korsós 2011; Golovatch 2014).

Golovatch (2014) questioned the attribution of T. jeekeli to Tonkinosoma, but now we rather believe that he somewhat misinterpreted the gonopodal structure of T. flexipes as described and illustrated by Jeekel (1953). Instead we follow Nguyen (2011) and consider both T. flexipes and T. jeekeli to represent congeners.

Prompted by the discovery of both T. flexipes and a third, new species of Tonkinosoma in southern China, the latter species the first to be found in caves, their descriptions are provided below. We also provide a key to all three presently known species of this genus.

Material and methods

All specimens used in this study were collected in southern China and preserved in 95% ethanol. Most of the type and non-type material is deposited in the Zoological Collection of the South China Agricultural University, Guangzhou, China (SCAU), with several samples also donated to the Zoological Museum, Moscow State University, Moscow, Russia (ZMUM), as indicated below.

Observation and dissections were performed using a Leica S8 APO stereo microscope. The line drawings were prepared with a Leica MZ125 microscope and a camera lucida attached to the microscope.

Photographs were taken with a Keyence VHX-5000 digital microscope, and further edited using Adobe Photoshop CS5.

Taxonomy

Key to species of Tonkinosoma

1 Body with a distinct colour pattern, yellowish brown to reddish brown (Figs 12). Epigean species 2
Body uniformly yellowish to pallid (Fig. 4). Presumably troglobitic species T. tiani sp. n.
2 A large, median, subquadrate process between ♂ coxae 4 and two small, independent tuberculations between ♂ coxae 5 (Fig. 2F) T. flexipes
Only two small and independent processes between ♂ coxae 4, without any modifications between ♂ coxae 5 T. jeekeli

Tonkinosoma flexipes Jeekel, 1953

Figs 1, 2, 3

Tonkinosoma flexipes Jeekel, 1953: 1, figs 1–4.

Tonkinosoma flexipes Nguyen 2011: 68.

Material examined

9 ♂, 1 ♀ (SCAU), 2 ♂ (ZMUM), China, Guangxi, Hechi City, Fengshan County, Jinya Town, Hangdong Village, 24°37'44"N, 106°51'26"E, 500 m a.s.l., 14.VI.2014, leg. Mingyi Tian, Weixin Liu, Haomin Yin & Xiaozhu Luo.

Remarks

This is the type species of Tonkinosoma hitherto known only from a highly detailed original description, based on the male holotype and two paratypes, one male and one female, all from Mt Manson, Langson Province, northern Vietnam (Jeekel 1953). Above is only the second record of T. flexipes, a species new to the fauna of China, but this is hardly too surprising because it comes from a place quite close to the border with northern Vietnam. The new samples almost fully agree with the original description (Jeekel 1953), but our material is remarkably smaller (19–28 mm vs. 37–47 mm). The habitus and gonopod structure (Figs 13) are illustrated to document the species’ identity. Among the main diagnostic characters of T. flexipes, the following seem to be especially noteworthy to complement the only available description: integument strongly shining; metazonae with several longitudinal striae above paraterga (Fig. 2C); pleurosternal carinae present on segments 2–4 in both sexes (Fig. 2C); a large, median, subquadrate process between ♂ coxae 4 and two small, independent tuberculations between ♂ coxae 5 (Fig. 2F); legs ca 1.6 (♂) or 1.2 (♀) times as long as midbody height, tarsal brushes present on all ♂ legs (Fig. 2I); gonopodal postfemoral part only indistinctly demarcated, lamina lateralis well-developed only in the proximal part of the solenophore (Fig. 3).

Figure 1. 

Tonkinosoma flexipes Jeekel, 1953 in nature. A a ♂ B a mating pair.

Figure 2. 

Tonkinosoma flexipes Jeekel, 1953, ♂. A–C anterior part of body, dorsal, ventral and lateral views, respectively D, E midbody segments; dorsal and subventral views, respectively F sternite V, ventral view G, H posterior part of body, dorsal and ventrolateral views, respectively I legs 3, 9, 16, anterior views. Scale bar: 0.2 mm.

Figure 3. 

Tonkinosoma flexipes Jeekel, 1953, ♂. A, B right gonopod, lateral and mesal views, respectively. Abbreviations: fe = femorite; ll = lamella lateralis; lm = lamella medialis; pf = postfemur; sg = seminal groove; sl = solenomere.

Tonkinosoma tiani sp. n.

Figs 4, 5, 6, 7, 8

Type material

Holotype ♂ (SCAU), China, Guizhou Province, Qianxinan, Anlong County, Sayu Town, Ganhan Dong Cave, 25°11'25"N, 105°19'31"E, 1250 m a.s.l., 12.V.2017, leg. Mingyi Tian, Weixin Liu, Xiaozhu Luo, Pingjing Yang & Yanyi Pu.

Paratypes

9 ♂, 20 ♀ (SCAU), same data as holotype. 8 ♂ (SCAU), same county, Longguang Town, Fengyan Dong Cave, 25°10'05"N, 105°13'50"E, 1400 m a.s.l., 12.V.2017; 13 ♂, 4 ♀ (SCAU), 1 ♂, 1 ♀ (ZMUM), Guizhou, Xingyi City, Wushan Town, Xiaozi Dong Cave, N 25°06'43", E 104°46'32", 1750 m a.s.l., 14.V.2017; all leg. Mingyi Tian, Weixin Liu, Xiaozhu Luo, Pingjing Yang & Yanyi Pu.

Name

To honour Prof. Mingyi Tian, one of the collectors from South China Agricultural University.

Diagnosis

This new species differs from its congeners in showing a largely unpigmented body. It seems to be especially similar to T. jeekeli on account of the particularly elongate and subcircular solenophore and solenomere, but differs by the strongly developed pleurosternal carinae present until segment 17 in both sexes, by an evident, subtrapeziform process between ♂ coxae 4, and the gonopod with a small and sharp tooth near the base of the solenomere.

Description

Lengths of both sexes ca 25–27 mm, widths 1.6–1.8 and 2.0–2.2 mm (♂) or 1.8–2.0 and 2.2–2.5 mm (♀) on pro- and metazonae, respectively. Holotype ca 27 mm long, and 1.8 and 2.2 mm wide on midbody pro- and metazonae, respectively.

Live coloration rather uniformly yellowish to pale (Fig. 4).

Body with 20 segments. In width, collum < head = segment 3 < 2 = 4 < 5–7 < 8–16, thereafter body increasingly tapered towards telson.

Head: frons densely pilose, vertex smooth, epicranial suture distinct (Fig. 5A–B). Antennae long and slender, reaching behind body segment 4 when extended posteriorly; in length, antennomere 2 > 3 > 5 > 4 > 6 > 1 > 7 (Fig. 5B–C).

Collum with 4+4 short setae at anterior margin. Following metaterga with traces of at least 1+1 setae before transverse sulcus, but pattern mostly vague and setae abraded. Paraterga of collum small, but evident, rounded. Paraterga 2 well-developed, directed down, with 4–5 clear lateral incisions on each side, frontolateral corner much sharper (Fig. 5A). Paraterga 3–6 each with three small, lateral incisions (Figs 5A), following paratergal incisions indistinct (Figs 5D, G, 6A). Calluses of paraterga 5–18 very thin in poreless segments, slightly thicker and sinuate in dorsal view in caudal 1/3 (ozopore position) of pore-bearing ones (Figs 5D, F, 6A–B); paraterga 19 nearly suppressed, but its ozopores clear (Fig. 5I).

Integument shining, texture of prozonae finely micro-alveolate. Stricture between pro- and metazonae broad and shallow, clearly ribbed (Figs 5D, 6A–B).

Pore formula normal (5, 7, 9, 10, 12, 13, 15–19), ozopores distinct, entirely lateral, lying inside an ovoid groove near caudal paratergal corner (Figs 5F, 6B).

Transverse sulcus incomplete on metaterga 4–7, more evident, complete and reaching bases of paraterga on metaterga 8–18 (Figs 5D, G, 6A). Axial line missing.

Epiproct tip truncated, with four spinnerets (Figs 5G–I). Paraproct with two setigerous knobs. Hypoproct roundly subtrapeziform, caudal setae distinctly separated, borne on evident knobs (Fig. 5H).

Pleurosternal carinae very strongly developed, present on segments 2–17 both in ♂ and ♀ (Figs 5C, F, 6B).

Sterna modestly setose, cross-impressions shallow (Fig. 5E). An evident, apically setose, subtrapeziform process between ♂ coxae 4 (Fig. 6C).

Legs long and slender, ca 2.5 (♂) or 2.0 (♀) times as long as midbody height. Tarsal brushes present only on ♂ legs 1–7, following legs normal, unmodified (Fig. 6D).

Gonopods (Figs 6D, 7, 8) simple. Coxite relatively short, about half as long as telopodite, poorly setose both distodorsally and distoventrally. Prefemoral portion densely setose as usual, about as long as coxite. Femorite (fe) long and slender, slightly curved mesally and faintly enlarged distally. An obvious demarcation sulcus (s) both laterally and dorsally between fe and a postfemoral portion (pf). Solenophore (sph) clearly coiled, circular, both lamina medialis (lm) and lamina lateralis (ll) well-developed and nearly entirely sheathing a similarly long and free solenomere (sl). Seminal groove (sg) running entirely on mesal side of femorite before moving onto sl, with a very small, sharp, mesal tooth (t) on pf near sl base.

Remarks

The karstic Ganhan Dong cave where the holotype was taken is about 300 m long. All material was collected in areas of complete darkness.

Based on the largely unpigmented integument, the long legs (2.5 (♂) or 2.0 (♀) vs. 1.6 (♂) or 1.2 (♀) times as long as midbody height in T. flexipes) and the cave habitat, this species seems to be a troglobite.

Figure 4. 

Tonkinosoma tiani sp. n. in nature A, B two different ♂ paratypes.

Figure 5. 

Tonkinosoma tiani sp. n., ♂ paratype from Ganhan Cave. A–C anterior part of body, dorsal, ventral and lateral views, respectively D–F midbody segments; dorsal, ventral and lateral views, respectively G–I posterior part of body, dorsal, ventral and lateral views, respectively. Scale bar: 0.2 mm.

Figure 6. 

Tonkinosoma tiani sp. n., ♂ paratype from Ganhan Cave. A, B segments 6–8, dorsal and lateral views, respectively C sternite V, ventral view D gonopods in situ, ventral view E legs 4 and 9, anterior view. Abbreviations: b = tarsal brush; o = ozopore; pl = pleurosternal carina.

Figure 7. 

Tonkinosoma tiani sp. n., ♂ paratype from Ganhan Cave. A–C left gonopod, mesal, anterior and lateral views, respectively. Abbreviations: fe = femorite; ll = lamella lateralis; lm = lamella medialis; pf = postfemur; s = sulcus; sg = seminal groove; sl = solenomere; sph = solenophore; t = tooth.

Figure 8. 

Tonkinosoma tiani sp. n., ♂ paratype from Ganhan Cave. A, B left gonopod, submesal and lateral views, respectively. Abbreviations: s = sulcus; sl = solenomere; sph = solenophore; t = tooth.

Discussion

The above record of T. tiani sp. n. in caves in southern China is remarkable at least in two ways. Firstly, the huge family Paradoxosomatidae only rarely occurs in caves, with only few presumably troglobitic species. The only exceptions are in the large genus Desmoxytes Chamberlin, 1923, which is very common both in epigean and subterranean environments across southeast Asia and China, and in the small genus Piccola Attems, 1953, with a few epigean species in Vietnam and Laos, and a single troglobitic one from Guangxi, China (Liu and Tian 2013; Golovatch 2015b). Secondly, biogeographically the situation concerning the distribution pattern of Tonkinosoma strongly resembles that not only of Piccola, but of still another millipede genus, i.e., Pacidesmus Golovatch, 1991 (Polydesmida, Polydesmidae). The latter genus has one high-mountain species in northern Thailand and a further eight, all presumed troglobites, in southern China (Golovatch and Geoffroy 2014).

Further research on cave millipedes of China will definitely reveal not only new interesting taxa, but more cases of remarkable distribution patterns.

Acknowledgements

We are particularly grateful Prof. Yuanhai Zhang (Institute of Karst Geology, Chinese Academy of Geological Sciences, Guilin) for his invitation and arrangements. We would like to thank “Xiongda” (Dr. Philip John Rowsell, Hongmeigui Cave Exploration Society), “Dudou”, “Jiuyao” and “Laocai” (Jinzhou Cave Exploration Club, Xingyi, Guizhou) for their invaluable assistance during our survey in the Qianxinan Autonomous Prefecture. Thanks also go to the caving team of the South China Agricultural University, Guangzhou, China, for their assistance in the field. We heartily thank three reviewers, R. Mesibov, D. VandenSpiegel, and P. Decker, for their help in critically reading and improving the paper.

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