The millipede genus Tetracentrosternus Pocock, 1895 (Polydesmida, Paradoxosomatidae, Alogolykinae, Alogolykini), with a description of the first, new species from Thailand

Abstract The millipede subfamily Alogolykinae and the tribe Alogolykini are recorded in Thailand for the first time,being represented there by Tetracentrosternus theelorsuensis sp. n. While the new species has characteristics that place it in the genus Tetracentrosternus, it also shows a number of unique features that make it necessary to rediagnose this Oriental genus, as well as to key its three currently known species and map their distributions. The tribes Alogolykini and Polydrepanini, as well as the subfamily Alogolykinae are also briefly redefined.


Introduction
The family Paradoxosomatidae has long been known to dominate the millipede fauna of the Oriental realm, including Thailand (Jeekel 1968). Thus, this family accounts for about half of the country's known diplopod species richness (Enghoff 2005). According to our latest estimates, Thailand currently supports 161 nominal species of Diplopoda, of which 71 (about 44%) are paradoxosomatids. They all belong to the nominotypical subfamily Paradoxosomatinae.
All the more interesting is the discovery in Thailand of the first species of the small, purely Oriental subfamily Alogolykinae. This new species, belonging in the small genus Tetracentrosternus Pocock, 1895 from the tribe Alogolykini, is described below. Several of its characters are so peculiar that the genus requires a redefinition.

Material and methods
The material was collected during a field trip in January 2011 from near Thee Lor Sue Waterfall in the mountains at the frontier between Thailand and Myanmar. Live animals were photographed on the spot. Specimens were preserved in 75% ethanol and studied in the laboratory using an Olympus stereomicroscope. Scanning electron micrographs (SEM) of the right gonopod coated with gold were taken using a JEOL, JSM-5410 LV microscope, returned to alcohol upon examination. Digital images of the specimen were taken in the laboratory and assembled using the "Cell D " automontage software of the Olympus Soft Imaging Solution GmbH package. In addition, line drawings of the left, completely intact gonopod were also prepared. All material is housed in the Museum of Zoology, Chulalongkorn University (CUMZ), Bangkok, Thailand. Diagnosis. Body medium-sized (ca 20-30 mm long, ca 2.0-3.2 mm wide), with 20 segments. Paraterga moderately to strongly developed. Sterna unmodified or with a cone near each coxa. Sternal lobe or cone(s) between ♂ coxae 4 present. First pair of ♂ legs with or without femoral adenostyles. At least some male legs with ventral brushes on tarsi, sometimes also on distal halves of tibiae.

Systematics
Gonopod with a quite short, subcylindrical, distoventrally densely setose coxite; prefemoral (= setose) part of telopodite short to very short, a quarter or less as long as acropodite, delimited from extremely short femorite by a mesal sulcus, ridge or spine; femorite supporting a long, spiniform, sometimes deeply bipartite femoral process (fp) and a similarly long to longer, flagelliform solenomere (sl), both more or less clearly sheathed by a mesal fold in basal half of acropodite. The latter suberect to strongly unciform, distal quarter to third with or without evident processes, clearly fimbriate and/ or fringed, often phylloid as well.
Remarks. Both Tetracentrosternus Pocock, 1895 and T. subspinosus Pocock, 1895 were originally diagnosed and described too briefly to be readily recognizable. The species was based on a few specimens taken by L. Fea and E. W. Oates at Puepoli (900-1,200 m a.s.l.) and Bia-po, now Carin Cheba (1,000-1,200 m), both in Myanmar (Pocock 1895, Thorell 1895. These two localities lie in the Karin Hills of southeastern Myanmar, in the Tenasserim Mountain Range adjacent to Thailand (Fig. 4).
The sole male of the species, from Puepoli and kept in the British Museum, was redescribed by Hoffman (1963) who designated it as lectotype. Hoffman was the first to provide clear illustrations of its gonopod structure, resulting in the establishment of a new tribe, Alogolykini, to encompass Tetracentrosternus, Alogolykus Attems, 1936and Touranella Attems, 1937(Attems 1936, 1937, 1938. Jeekel (1965) redescribed this species in more detail not only from the lectotype, but also from the paralectotypes (from Carin Cheba) still housed in the Genoa Museum. He made new, even more accurate illustrations and a highly detailed redescription, fully accepting the tribe and adding thereto also Yuennannina Attems, 1936. A little later, Jeekel (1968) elevated the tribe Alogolykini to the status of a subfamily, Alogolykinae, adding thereto a new tribe, Polydrepanini. Jeekel transferred Touranella from Alogolykini to Polydrepanini, because the genus lacks adenostyles on the femora of the male first legs, as do the other constituent genera of the latter tribe.
The new species described below, despite its relative geographical proximity to T. subspinosus, shows a number of characters so different that the diagnosis of the genus needs to be refined. Thus, because there are no adenostyles in femora 1 of the male of T. theelorsuensis sp. n., this trait can be regarded as only species-specific not only in Tetracentrosternus, but in the entire subfamily Alogolykinae. So, following Hoffman (1963), it seems best to return Touranella (three species in Vietnam, one in Nepal) to Alogolykini, as its close similarities to Tetracentrosternus are apparent. The only meaningful differences lie in gonopod structure, the femoral portion in Touranella some-times being a little longer, the solenomere a little thicker, suberect and rod-shaped rather than flagelliform, while the femoral process when present is considerably shorter (Golovatch 2009a(Golovatch , 2009b. In our opinion, a strong, rod-shaped solenomere versus a thin, flagelliform one remains the basic difference between the tribes Alogolykini and Polydrepanini, respectively. Thereby the subfamily Alogolykinae seems to be best characterized only by the absence of a clear-cut division of the solenophore or solenophore-like structure near/around the solenomere into a membranous lamina medialis and/or a similarly membranous lamina lateralis, in Polydrepanini often coupled with a twisted, helicoid course of the seminal groove. In addition, the gonofemorite in Alogolykinae is often strongly abbreviated while many species show adenostyles on the male first femora. The latter two traits are also characteristic of the subfamily Australiosomatinae, but the solenophore branch or branches remain free and never sheath a primitively long, strong and rod-like solenomere. A more detailed review of these subfamilies and their tribes (see Jeekel 1968) lies far beyond the scope of the present note.
The gonopod telopodite in Tetracentrosternus theelorsuensis sp. n. is strongly elongate and unciform, bearing three evident processes in the distal half, whereas the solenomere is particularly long and nearly as long as the solenophore, while the femoral process is also very long, but deeply bipartite. Besides this, as in T. subspinosus, the strongly abbreviated gonofemoral part in the new species is delimited distally by a distinct ridge, as opposed to a strong spine in T. hoffmani.
In terms of metatergal structure, T. theelorsuensis sp. n. is somewhat intermediate between both congeners, the tegument being only moderately rugulose as opposed to nearly smooth in T. subspinosus or rather clearly tuberculate in the rear halves of metaterga in T. hoffmani.
There is little doubt that more species of Tetracentrosternus await discovery at least in and between eastern Myanmar and southern China, including Thailand (Fig. 4). The same certainly holds true for some other Alogolykini as well, e.g. Touranella. Name. After Thee Lor Sue Waterfall, the type locality, which is the largest and highest waterfall in Thailand.

Diagnosis.
Differs from congeners mainly by the first pair of ♂ legs lacking femoral adenostyles, coupled with unmodified sterna and the distal half of the gonopod telopodite being strongly curved, elongate and distally carrying three evident processes. See also Remarks above and Key below. Coloration of live animals dark brown (Fig. 1A); paraterga, legs and epiproct light brown, head, collum and metazona 2-4 blackish, following terga with a blackish triangle covering both pro-and metazona; coloration of alcohol material after 2 years of preservation faded to whitish or yellow with a pattern of a contrasting dark brown triangle at posterior edge of pro-and metazona, castaneous brown below paraterga; head and antennomeres 6 and 7 brown to castaneous brown; venter and a few basal podomeres light brown to yellow-brown, legs growing infuscate (brown) distally; tip of antenna pallid (Fig. 1A-H).