The first record of the millipede genus Streptogonopus Attems, 1914 from Vietnam, with description of a new species (Diplopoda, Polydesmida, Paradoxosomatidae)

Abstract This paper describes a new species of the millipede genus Streptogonopus Attems, 1914, Streptogonopus montanus sp. n. from Vietnam, the first record of Streptogonopus in Vietnam. The new species is characterised by the solenophore completely sheathing the solenomere, both coiled twice, and the solenophore with a small spine at its middle. The species was found at ca. 1,800–2,100 m on Ngoc Linh Mountain. This first record for the genus in the Indochina peninsula has expanded its distributional range to the easternmost part of Southeast Asian mainland. An identification key to Streptogonopus species is also provided.

Currently, the genus Streptogonopus Attems, 1914 comprises only five valid species: S. neglectus from Eritrea; S. phipsoni from India, Pakistan, Bangladesh and Nepal; S. jerdani, S. nitens, both from India; S. degerboelae, from Thailand. This work provides the first record of the genus in Vietnam with the description of a new species.

Materials and methods
Material examined was collected from the Ngoc Linh Mountain, the second highest mountain in Vietnam (ca. 2,600 m a.s.l.). All material was preserved in ethanol 80% and is housed in the Institute of Ecology and Biological Resources (IEBR), Vietnam Academy of Science and Technology, Hanoi, Vietnam.
Gonopods were removed for morphological examination. Only the left gonopod of holotype was coated with gold for scanning electron microscopy (SEM) using an ABT 32 scanning electron microscope. Line drawings were made using an Olympus microscope SZX10. Digital images were taken using a camera Infinity3 Lumenera attached to a Leica M205C stereomicroscope and stacked using the software I-Solutions.
Diagnosis. Jeekel (2004) stated that the genus can be recognised by the paraterga being small or completely reduced; the gonopod femorite erect, narrow at the base and widening abruptly; demarcation between femorite and postfemoral region present; the solenomere and solenophore twisted one or two times; and the solenomere completely sheathed by solenophore.
Remarks. The genus can be separated into two small groups based on the absence or presence of paraterga. The former group contains S. jerdani and S. degerboelae, the latter comprises S. neglectus, S. phipsoni, and S. nitens. Diagnosis. This species is recognised by the gonopod femorite grooved mesally, slightly curved and expanded distally, without processes; solenophore and solenomere coiled twice, equal in length. Solenophore with a small spine at ½ its length.

Streptogonopus montanus
Etymology. "montanus", an adjective to emphasise that the species has been found in a mountainous region.
Legs (Figs 1A-E) thin and slender, about 1.3 times as long as midbody height. Prefemora not swollen. Femora without modification. Tarsal brushes present only on pre-gonopodal legs.
Remarks. This new species could be assigned to the second group characterised by modestly developed paraterga. However, it differs from three its congeners, S. neglectus, S. phipsoni, and S. nitens in solenomere and solenophore being equal in length and strongly coiled twice and the solenophore having a small spine at its middle.

Key to species of the genus Streptogonopus Attems, 1914
(based on the keys compiled by Jeekel (1956) and Attems (1936)

Discussion
The genus is known to occur in Eritrea, India, Pakistan, Bangladesh, Nepal and Thailand (Nguyen and Sierwald 2013;Shelley 2014;Golovatch 2015). The discovery of a new species in Vietnam has expanded the distribution range of the genus Streptogonopus to the easternmost part of the Southeast Asian mainland. However, there is still a gap in the distribution with no records reported from Myanmar, Laos and Cambodia (Nguyen and Sierwald 2013;Likhitrakarn et al. , 2015. The new species was found at a high elevation (ca. 1,800-2,100 m a.s.l.) on Ngoc Linh Mountain (Kon Tum Province), the second highest mountain, in Vietnam and is thus unlikely to be an introduction due to human activities. The relatively few records for the genus indicates that there are likely to be more Streptogonopus species awaiting discovery in Indochina and its adjacent regions.
Being located in the Burmese-Indochinese Biodiversity Hotspot (Sterling et al. 2006), Vietnam is known to have a rich fauna including millipedes. The discovery of the millipede genus Streptogonopus in Vietnam indicates that the Vietnamese millipede fauna may be richer at genus level than previously suspected.