A new species and a new record of the Southeast Asian millipede genus Antheromorpha Jeekel, 1968 (Polydesmida, Paradoxosomatidae) from Vietnam

Abstract Antheromorphanguyenisp. n. is described and illustrated from Kon Ka Kinh National Park, southern Vietnam. The new species is distinguished by a peculiar colour pattern showing a uniformly black-brown body contrasting with yellow-brown paraterga and epiproct, as well as in the pointed gonopodal process being unusually short, only approximately half as long as the solenophore. In addition, an identification key to all 13 presently known species, all mapped, is given. A new record of A.festiva is provided from southern Vietnam.


Introduction
The Southeast Asian millipede genus Antheromorpha Jeekel, 1968 was established to replace Brachytropis Silvestri, 1896 which had been preoccupied by Brachytropis Fieber, 1858, a genus of Hemiptera (Jeekel 1968). It was later redefined, especially against the similarly large-bodied, even more species-rich, and mostly sympatric genus Orthomorpha Bollman, 1893, with some Burmese species revised and a few new synonymies proposed based on type material (Jeekel 1980). Antheromorpha has since been reviewed and rediagnosed, with even more synonymies established, and most species likewise redescribed, based both on type and fresh material (Likhitrakarn et al. 2016).
It was Attems (1937) who described the first member of this genus from Vietnam, Orthomorpha harpaga Attems, 1937, from Hon Ba Mountain in the south-central part of the country. Jeekel (1968Jeekel ( , 1980 correctly transferred it to Antheromorpha. Likhitrakarn et al. (2016) have since redescribed this species from the types, while Golovatch and Semenyuk (2018) have freshly documented and illustrated it from Kon Ka Kinh National Park, Gia Lai Province, central highlands of Vietnam. Nguyen et al. (2018) have recently reviewed Antheromorpha in the scope of the Vietnamese fauna, described a new species, A. pumatensis Nguyen, Nguyen & Le, 2018 from Nghe An Province, north-central Vietnam, and provided additional records of A. paviei (Brölemann, 1896) from Ba Na National Park, Da Nang Province, and of A. festiva (Brölemann, 1896) from Kien Giang, Dak Lak and Tay Ninh provinces (Fig. 5).

Materials and methods
The material documented below was collected by one of us (Irina Semenyuk abbreviated IS), according to Agreements 432/TCLN-BTTN and 142/SNgV-VP between the Kon Ka Kinh National Park and the Joint Russian-Vietnamese Tropical Center, as part of IS's research project on the diversity, biology, and ecology of millipedes in Vietnam.
Live animals were photographed in their habitats using a Canon 70D digital camera with a Canon PowerShot A4000IS 16.0 MP Digital Camera. Specimens were preserved in 75% ethanol, and morphological investigations were carried out in the laboratory using an Olympus stereo microscope. Scanning electron micrographs (SEM) of gold-coated gonopods were taken using a JEOL, JSM-5410 LV microscope. Specimens were also photographed and the images stacked in the laboratory using the "CellD" automontage software of the Olympus Soft Imaging Solution package, while the gonopods of a paratype were dissected and illustrated under Euromex iScope microscopes. Almost all material is housed in the Zoological Museum, State University of Moscow (ZMUM), Russia, with one paratype donated to the collection of Chulalongkorn University's Museum of Zoology (CUMZ), Bangkok, Thailand.
In the synonomy section given below, D stands for a description or descriptive notes, R for a new record or records, while M for a mere mention. Other abbreviations are:  Remarks. The new specimens fully agree with the detailed and beautifully illustrated redescriptions of the species as given by Brölemann (1904) and Likhitrakarn et al. (2016). This is the first formal record of A. festiva in Cat Tien National Park. In that park, A. festiva shows a pronounced seasonal rhythm. According to several years of observation by one of us (IS), juveniles of different stages (from the 4 th to the last instar) start swarming in the autumn, just before the dry season. Swarms contain hundreds of millipedes slowly moving around and feeding. One swarm patch usually contains mainly same-age individuals ( Fig.  1). Even though swarms of different instars may appear next to each other, they normally do not mix. Patches of swarming are usually localized in secondary forest with dominating bamboo and in grasslands. Swarms of individuals of the latest instars are looser than those of earlier stages. Adults appear during the same season, but do not swarm. In the dry season, the abundance of A. festiva abruptly declines and then, in the early rainy season in summer, it gradually grows again to abruptly stop in the middle of the rainy season. Paratypes. 1 ♂ (ZMUM), same locality, together with holotype; 1 ♂ (ZMUM), same locality as holotype, but on top of a hill with cloud forest, 14°13'12"N,  (Brölemann, 1896) in Cat Tien National Park. Photographs by I Semenyuk.
Name. To honour Nguyen Duc Anh, the leading Vietnamese myriapologist. Diagnosis. Differs from congeners mainly in the colour pattern (a uniformly blackbrown body with contrasting yellow-brown paraterga and epiproct), as well as in gonopod process d being unusually short, approximately half as long as the solenophore.
Gonopods (Figs 3, 4) simple, with femorite ca. 3 times as long as prefemoral (= strongly setose) part. Femorite moderately curved caudad, postfemoral portion demarcated by an oblique lateral sulcus; solenomere flagelliform, almost fully sheathed by solenophore, tip of solenophore very deeply bifid; with a rather long, slender, fully pointed process d; process m with a narrowly rounded terminal lobule, longer than a small, rounded process v with a very small, middle, spiniform prong.
Remarks. Adults of the new species were found in May during a short expedition to a small area within Kon Ka Kinh National Park near its headquarters. A prospected forest with a similar forest structure within the same park near the village of Krong (N14°17', E108°26', 700-1000 m a.s.l.), ca. 14 km NE of the type locality, failed to reveal this species. It co-exists at the type locality together with Orthomorpha scabra Jeekel, 1967 and three other Orthomorpha species, all apparently undescribed. According to IS' observations, the five species share the same microhabitats. Given the conspicuously large and similar sizes of the adults of Antheromorpha and Orthomorpha, an ecological study of this syntopy in Kon Ka Kinh National Park would be worthwhile.
Although our new species is superficially very similar to Orthomorpha species such as O. elevata Likhitrakarn, Golovatch & Panha, 2011, from Perak State, Malaysia, it is clearly different in the shape of the sternal lamina between ♂ coxae 4 and in gonopodal structure (Likhitrakarn et al. 2011).   (Figs 3, 4A, B)

Conclusions
The genus Antheromorpha belongs to the tribe Orthomorphini which currently contains 25 genera Sierwald 2013, Srisonchai et al. 2018a, b, c), this allocation being supported not only morphologically, but also by molecular evidence (Nguyen et al. 2018). Antheromorpha species range from southern China in the north, through My-  (13)  anmar, Thailand, Laos, and Vietnam, to Western Malaysia in the south (Fig. 5). Four species seem to be particularly widespread; thus, A. uncinata occurs all over Thailand and it has repeatedly been reported swarming in the northern parts of the country (Likhitrakarn et al. 2016). A similarly vast distribution is also characteristic of A. festiva, which has been recorded across the southern half of the Malay Peninsula (southern Thailand and Western Malaysia) to southern Vietnam. As the range of A. rosea covers southern China and northern Thailand, most probably it occurs also in eastern Myanmar. Finally, since A. paviei is known from southern Laos and Vietnam, it seems very likely that it should exist in Cambodia as well (Likhitrakarn et al. 2014) (Fig. 5). Moreover, further Antheromorpha species may well be revealed with additional collecting efforts, especially in poorly prospected places so numerous in the huge region involved (Likhitrakarn et al. 2016).