Review of the genus Tylopus Jeekel, 1968, with descriptions of five new species from Thailand (Diplopoda, Polydesmida, Paradoxosomatidae)

Abstract The genus Tylopus currently contains 41 species, all keyed and mapped, including five new from northern Thailand: Tylopus bispinosus sp. n., Tylopus grandis sp. n., Tylopus extremus sp. n., Tylopus veliger sp. n. and Tylopus parajeekeli sp. n. Species of Tylopus are predominantly forest-dwellers, especially in montane habitats where up to 9–10 species can coexist per faunule. We expect many more congeners to be discovered in future, in particular from poorly or relatively poorly prospected regions such as Laos (only two species recorded), Cambodia (no species yet), Vietnam (a few species), Myanmar (a few species) and southern China (one species only). Because the genus is so species-rich and as yet so poorly sampled, a phylogenetic analysis of Tylopus would be premature.


Gonopod structure
Tylopus is known to be defi ned, among other characters, by its relatively elaborate gonopod conformation, sometimes perhaps amongst the most complex not only in the tribe Sulciferini it belongs to, but also in the Paradoxosomatidae as a whole. Even though a thorough, still fully valid review of gonopod structure is available (Golovatch and Enghoff 1993), we feel tempted to reiterate here the main morphological terms before describing new species and providing some descriptive notes concerning already known congeners.
Th e gonopod telopodite in Tylopus usually shows a distinct transverse ring, or cingulum, demarcating the postfemoral region which starts at the base of a free, fl agelliform solenomere. Th e solenomere is largely sheathed by a slender and sigmoid solenophore usually bearing a number of outgrowths at its base. Th e cingulum is only rarely incomplete due to a somewhat reduced sulcus at the base of lobe l, like the one observed in T. grandis sp. n. (Figs 5 and 6). Usually lobe l is simple, but sometimes it can be crowned with a larger (e.g. T. extremus sp. n.,Figs 8 and 9,or T. veliger sp. n.,Figs 11 and 12) or smaller outgrowth (e.g. T. degerboelae,Figs 20 and 21,or T. nodulipes). In addition to lobe l, the postfemoral region is nearly always supplied with a more or less evident process h lying mesally of the lobe. However, h is absent from T. strongylosomoides. All other disto-and/or postfemoral outgrowths, based on their positions, appear to be even more optional. Th us, process z is mostly discernible, yet occasionally very small (e.g. T. parajeekeli,Figs 14 and 15,T. jeekeli,Figs 26 and 27,or T. hoff mani) to fully missing (e.g. T. degerboelae,Figs 20 and 21,T. haplorugosus,Figs 23 and 24,or T. prosperus,Figs 29 and 30). Only a few species appear to show particularly complex gonopods. Th en not only does the postfemoral region bear a long, spiniform process z, e.g. T. perarmatus (Figs 34 and 35), but also the femorite can be supplied with a small, inconspicuous, lobiform (e.g. T. tamdaoensis) to very long, knife-to spine-shaped, distodorsal outgrowth m (T. extremus sp. n., Figs 8 and 9, or T. perplexus). Besides this, even a few more structures can be added to the postfemoral region, as is observed in T. perplexus. It is the sizes and shapes of these various outgrowths that provide several further important species-specifi c characters in addition to a good number of peripheral ones (Golovatch and Enghoff 1993).

Name:
To emphasize the spiniform processes h and z of the gonopod. Diagnosis: Diff ers from congeners in both processes h and z of the gonopod being spiniform.
Gonopods (Figs 2, 3) with lobe l well-demarcated; spine h very small; spine z considerably more prominent. Name: To emphasize the large size of this species Diagnosis: Diff ers from congeners in the large size, coupled with a short spiniform process h, a basally only poorly delimited lobe l, and a small lobiform process z of the gonopod.
Gonopods (Figs 8,9) with lobe l well-demarcated, but unusually prominent, high and elongated; spine h long, extremely slender and subfl agelliform; spine z rather short and simple; spine m very prominent, straight and long. Name: To emphasize the velum-shaped end of gonopod lobe l. Diagnosis: Diff ers from congeners except T. perplexus Golovatch & Enghoff , 1993 in the distal part of gonopod lobe l being velum-shaped and supplied with two denticles, from T. perplexus in the gonopod lacking spines m and q, as well as in a much shorter and knife-shaped spine z, and a rudimentary spine h.
Gonopods (Figs 14, 15) with lobe l well-demarcated; spine h small, but elongate, not bifi d; spine z very small, dentiform, placed at base of spine h.

New faunistic records
Th e following seven species have been illustrated in additional detail to confi rm their identities, as well as to provide further information concerning both their variation and distribution.

Tylopus prosperus Golovatch & Enghoff , 1993 Figs 28-30
Tylopus prosperus Golovatch & Enghoff , 1993: 93. Tylopus prosperus: Enghoff , 2005: 99.  Remarks. Th is strictly topotypic material fully agrees with the original description (Golovatch and Enghoff 1993), showing no evident variation in peripheral and gonopod structure (Figs 28-30).      Remarks. Th is near-topotypic material fully agrees with the original description (Golovatch and Enghoff 1993), showing no evident variation in peripheral and gonopod structure (Figs 31-33).          Remarks. Th is species has long been known as perhaps the most widespread and common congener in northern Th ailand, also showing considerable variation both in body texture and gonopod structure (Golovatch and Enghoff 1993). Th e new samples add to this variation in the gonopods often with spine h rather narrow and spiniform to broadly denti-or lobiform, and spine z nearly straight to strongly unciform (Figs 34-38).

Conclusion
Tylopus appears to be one of the largest millipede genera in Southeast Asia. Th e genus is best known from Th ailand, which has 26 (> 63%) of the described species. With further progress in our knowledge of the millipede faunas of other, still poorly prospected, mostly neighbouring countries such as Laos, Myanmar, Cambodia and Vietnam, as well as southern China, the total of 41 Tylopus species can readily be expected at least to double. More congeners are likely to be found in Th ailand as well. Golovatch and Enghoff (1993) attempted a preliminary phylogenetic analysis of Tylopus based on the 35 species then known, but given the incomplete state of our knowledge of Tylopus, we believe that a new phylogenetic analysis would be premature.
In Th ailand, all Tylopus are confi ned to the northern, mountainous parts of the country (Map). Finding congeners south of Tak Province seems unlikely, but, since Tylopus are known also from all over Vietnam, including the southern parts of the country, this genus is likely to occur at least in the adjacent parts of Cambodia, from where no species have hitherto been recorded. At present the northern range limit of Tylopus lies in Yunnan Province, China, but it seems plausible that many more regions in southern China, even some north of Yunnan, might also prove to support Tylopus species. Since only a few species have been reported from Laos and Myanmar, another considerable increase in the number of congeners is more than likely after further collecting in those countries as well.
Almost all Tylopus species are confi ned to forest habitats, especially montane ones. Most are local to highly local in distribution. Th ere are only very few relatively widespread congeners, e.g. T. doriae, T. perarmatus or T. degerboelae. At one locality, as many as nine congeners can co-occur, e.g. in Doi Inthanon and Doi Suthep mountains. Th is remarkable result indicates that many other high-to mid-montane forested areas in Indochina and southern China could support similarly rich faunules of Tylopus.
Within Tylopus sympatric groups, only T. degerboelae appears to show a highly extended, almost annual pattern of seasonal activity, judging from the occurrence of adults of both sexes at Doi Inthanon and, especially, Doi Suthep. Adults of the bulk of congeners living at either (four species each) or both (fi ve species) of these mountain ranges tend to be autumnal, their collection being confi ned to September to November. Th is probably means that these species represent a single, autumnal phenofauna. Th e sole, possibly noteworthy exception is T. asper which has heretofore been found only at Doi Inthanon and only in May. Whether this species represents a diff erent phenofauna or not, remains open to question. Special observations are required to reveal the phenology and breeding seasons of Tylopus at least in northern, mostly montane Th ailand.