Sinostoma yunnanicum, Martens, Jochen, 2016

Martens, Jochen, 2016, Sinostoma yunnanicum, the first nemastomatine harvestman in China (Arachnida: Opiliones: Nemastomatidae), Zootaxa 4126 (3), pp. 444-450 : 445-449

Sinostoma yunnanicum n. sp.

Figs 1 – 13

Holotype ♂ ( SMF): CHINA, North Yunnan, Zhongdian County (now Shangri-La County), 55 km north of Zhongdian (now Shangri-La City), 3800m, 28°19.8’N 99°45.7’E, primary mixed forest, Rhododendron , dead wood, leaf litter, mushrooms, moss; from soil litter, D.W. Wrase leg. 18.8.2003.

Diagnosis. The sole species of Sinostoma with the characters of the genus.

Measurements. ♂: body-L: 1.7, only dorsal scutum: 1.5; Leg II: Fe 1.2, Pt 0.4, Ti 0.8, Mt 1.6 Ta 1.3; Penis-L: 0.9. ♀ unknown.

Description. Body ( Figs 1 – 3 ): Dorsal side; scutum uniformly dark brown, without any golden or silvery markings. Margins of scutum from anterior to posterior part with a continuous row of narrowly positioned anvilshaped low tubercles, partly fused into a low uninterrupted wall or line.

Second thoracic segment and segments (areae) I – V of scutum separated by lines of anvil-shaped tubercles similar to those on peripheral margins of the scutum, this line bent forward on area I, bent backward on areas III, IV and V caudally forming a distinct network encircling the dorsal scutal plate and separating the five dorsal areas from each other. Areas I – V with para-median pairs of low pegs, slightly inflated distally, rounded at upper end, from area I to area V lengths of pegs slightly increasing, lacking on area II. Beside the pegs areas I – V with few additional scattered low tubercles, several of them anvil-shaped. Tu oc low, touching front of scutum and densely covered by large anvil-shaped tubercles.

Ventral side: Cx I – IV each with a pro- and retro-lateral row of strong anvil-shaped tubercles, rear and front row of consecutive Cx touching each other. Op gen covered by scattered low rounded tubercles; free sternites with few tubercles at margins; all light brown.

Legs: Short and stout (in terms of nemastomatid morphology); Fe, Pt and Ti of leg I slightly inflated, Fe, Pt and Ti of all legs densely covered by stiff, short bristles, partly with small spines, less so on Mt and Ta, there few scattered long hairs. There are no “comb-teeth” (Kammzähnchen) as figured by Gruber (1976) for Mediostoma .

Pedipalp ( Fig. 13 ): Moderately short, Fe slightly swollen distally, Pt slightly enlarged ventrally, Ti slightly tapering distally; Ta short and rounded; all members bearing clavate setae, most conspicuous on Pt, Ti and Ta. No article with special armament.

Chelicera ( Figs 4 – 7 ): Rather stout; basal article with a bulky frontad-directed Apo slightly surpassing the front margin of basal article; Apo with a broad basis, longer than high (lateral view), upper side smoothly rounded and dorso-distally projected in a pointed hook. In dorsal view Apo less pointed, markedly directed to medial side. Medially, the Apo is excavated nearly over its total length forming a bowl-like excavation or hole. Its inner wall is perforated by a multitude of minute pores, apparently the secretion area of the cheliceral gland. Second cheliceral article moderately inflated with few long scattered bristles.

Genital morphology ( Figs 8 – 12 ): Truncus penis ( Figs 8 – 9 ) moderately slender; the basis forming a large inflated bulb well separated from the remainder of the truncus; bulb compact, not incised on its median plane, completely filled by the two penial muscles, their tendons spanning truncus longitudinally to base of glans. Truncus narrowest above the bulb (dorsal/ventral views), slightly enlarging to the distal third, then inflated slightly more strongly to form a symmetrical blade which finally tapers to the glans. Glans ( Figs 10 – 12 ) only inconspicuously marked, short, starting where the two tendons touch and insert on the inner truncus wall; stylus short, a continuation of the glans tapering to the distal asymmetrical opening of the seminal duct. Glans armed with short, stiff and unspecialized spines, arranged symmetrically in dorsal and ventral views, six on the dorsal, five on the ventral side.

Name. It refers to the Chinese province Yunnan, the origin of this species.

Distribution. The species is known only from the type locality, where it was collected in an old-growth coniferous forest at 3800 m with dense understory including a Rhododendron layer.

Discussion. As proposed by Gruber & Shear (1983) the Nemastomatidae are divided into two subfamilies, Nemastomatinae and Ortholasmatinae. The former is restricted to the Palaearctic Realm with a strong bias to the western Palaearctic, especially in mountainous areas in south-western, central and western Europe. The Balkan Peninsula, Pyrenees and Cantabric Mts., the Caucasus and Turkey are centres of nemastomatine diversity. Several of these areas, especially the Caucasus ( Martens 2006), harbor endemic genera and, additionally, display remarkable radiations of small-range species ( Schönhofer 2013).

In Sinostoma yunnanicum only one distinct morphological character is prominent, the short glans of penis. Generally, its proximal part is demarcated by the insertions of the penial tendons within the truncus. These extend from the two basal muscles along the truncus to the glans. In addition, the glans in turn is marked by the scanty but obvious armament of robust spines. Accordingly, a similar short glans is characteristic of the genus Starengovia Snegovaya, 2010, but it is more slender in comparison and the stylus rather long and it represents also an East Palaearctic genus (one species in Kyrgyzstan and the Northwest Himalaya each, the latter undescribed). Starengovia in turn is unique by its broad foliate alate structure of distal part of truncus ( Snegovaya 2010), which is lacking in Sinostoma . Both genera may represent a common phylogenetically and geographically isolated evolutionary line within Nemastomatinae. With respect to an evolutionary tree based on molecular genetics ( Schönhofer & Martens 2012) they may have diverged near the base of the tree.

A distinctive bowl-like medial excavation on the male cheliceral apophysis occurs in several nemastomatine genera and may have developed independently several times. This can be inferred from the placement of the relevant genera on the molecular tree ( Schönhofer & Martens 2012). Nemastomella and Mediostoma , genera screened so far, are not closely related and are restricted to the Iberian Peninsula or range from the Balkans to the Caucasus, respectively. A very similar apophysis form in Sinostoma possibly represents another parallel development rather than indicating close relationship. The placement of the secretion area on the male cheliceral apophysis varies among species and strongly varies among genera of nemastomatines. The secretion plays a role during courtship ( Martens 1969, Martens & Schawaller 1977).

Sinostoma yunnanicum is the easternmost representative of Nemastomatinae. The nearest nemastomatine localities to the west are the Central Asian Tadjik Pamir Mts. (“ Mediostoma ” pamiricum Starega, 1986) and the Nature Reserve Sari-Tshelek in Kyrgyzstan (Starengovia kirgisicum Snegovaya, 2010), both apparently extremely localized endemics known from a single locality each. However, in Himalayan Northwest Pakistan an undescribed Starengovia species is present (J.M. unpublished). The latter locality reduces the distance to the Sinostoma locality to about 3000 km. Despite intensive sampling of small soil arthropods by workers of the Geneva Natural History Museum and the Mainz Institute of Zoology in many parts of the western and central Himalayas, no nemastomatids have turned up except for the sole Pakistan location. The only former mention of nemastomatids on the Indian Subcontinent was presented by Roewer (1959), long since identified as a false record not to be mentioned further ( Schönhofer 2013). Though more Nemastomatinae species will certainly be discovered in China, the group seems to be rare and locally distributed, probably confined to mountainous old-growth forests as relicts. According to its distribution in Southwest China, a core area of many old endemic animal groups, Sinostoma may be a basally derived member of the nemastomatine phylogenetic tree opposite Mitostoma .

Figures

FIGURES 1 – 3. Body, Ƌ holotype, 1: lateral side, 2 – 3: dorsal side. Scale bar 0.5 mm.

FIGURES 4 – 7. Ƌ right chelicera, 4: medial side; 5 – 7: apophysis of Ƌ chelicera from 5: lateral, 6: medial and 7: dorsal side. Scale bars: Fig. 4 0.1 mm, Figs 5 – 7 0.05 mm.

FIGURES 8 – 13. Genitalia and pedipalp. 8 – 9: truncus penis, dorsal and lateral views, 10 – 12: glans penis from 10: lateral, 11: dorsal and 12 ventral views. 13: Ƌ pedipalp, medial view. Scale bars: Figs 8 – 9 0.2 mm, Figs 10 – 12 0.05 mm, Fig. 13 0.2 mm.