Trichopolydesmidae from Cameroon, 2: A species-level reclassification of Afrotropical trichopolydesmids (Diplopoda, Polydesmida), with two new species and two new records from Cameroon, and two new species from the Nimba Mountains, Guinea

Abstract A revised classification of Afrotropical Trichopolydesmidae is presented. The fauna presently contains as many as 52 species in six recognized genera, with numerous new transfers/combinations involved: Bactrodesmus Cook, 1896 (3 species, including B. grandissp. nov. from the Nimba Mountains, Guinea), Eburodesmus Schubart, 1955 (2 species), Hemisphaeroparia Schubart, 1955 (26 species, including one old species, Polydesmus parvulus Porat, 1894, revised from type material and provisionally assigned to Hemisphaeroparia, as well as two new records and two new species from Cameroon: H. longibrachiatasp. nov. and H. avissp. nov.), Mecistoparia Brolemann, 1926 (3 species), Physetoparia Brolemann, 1920 (12 species, including P. complexasp. nov. from the Nimba Mountains, Guinea), and Sphaeroparia Attems, 1909 (6 species). The hitherto enigmatic genus Bactrodesmus is redefined, but the monotypic Trichozonus Carl, 1905 still remains dubious.


Introduction
All Afrotropical genera of the millipede family Trichopolydesmidae have recently been reviewed based on their type species and a presumed scenario of gonopodal evolution (Golovatch et al. 2018). As a result, in addition to two still enigmatic genera, Bactrodesmus Cook, 1896 andTrichozonus Carl, 1905, only five genera have been regarded as currently recognizable: Sphaeroparia Attems, 1909, Physetoparia Brolemann, 1920, Eburodesmus Schubart, 1955, Mecistoparia Brolemann, 1926and Hemisphaeroparia Schubart, 1955. The last genus listed is the sole trichopolydesmid to occur in Cameroon and is especially diverse (26 species).
The present contribution provides a species-level reclassification of Afrotropical Trichopolydesmidae and gives a new diagnosis of Bactrodesmus based on the discovery of a new species from the Nimba Mountains, Guinea. Two additional records and two new species of Hemisphaeroparia are described from Cameroon, while the sole old and still enigmatic species reported from that country, Polydesmus parvulus Porat, 1894, is revised from female syntypes and is tentatively assigned to Hemisphaeroparia as well.
A new species of Physetoparia is also described from the Nimba Mountains, Guinea.

Material and methods
Most of the material treated here derives from the collection of the Musée Royal de l'Afrique Centrale (MRAC), Tervuren, Belgium, with only a few duplicates retained for the collections of the University of Yaounde 1 (UY1), Cameroon or donated to the Zoological Museum, State University of Moscow (ZMUM), Russia, as indicated below. The samples are stored in 70% ethanol. Specimens for scanning electron microscopy (SEM) were air-dried, mounted on aluminium stubs, coated with gold and studied using a JEOL JSM-6480LV scanning electron microscope. The colour pictures were taken using the focus stacking setup described by Brecko et al. (2014). Canon EOS Utility software was used to control the camera. Zerene Stacker was applied for stacking the individual pictures into one 'stacked image'.
The abbreviations used to denote gonopodal structures are explained directly in the text and figure captions.
6. Sphaeroparia uncinata Brolemann, 1920, Mount Kenya, Kenya (Brolemann 1920. The above list contains 52 species, including 26 in Hemisphaeroparia, 12 in Physetoparia, six in Sphaeroparia, three each in Mecistoparia and Bactrodesmus, and two in Eburodesmus. One more species remains in the dubious genus Trichozonus (see below). We describe here another four new species in three genera and clarify the identity of Bactrodesmus. Additional records of two species recently described from Cameroon are also presented. Diagnosis. Differs from all other species of the genus by the unusually complex gonopodal structure, i.e. the presence of a particularly prominent, distolateral, gonocoxal lobe (lo) that protects a similarly clearly exposed telopodite, the latter being largely represented by a high apicomesal lobe/outgrowth (ab) that carries a highly peculiar, large, tube-shaped solenomere (tu). The gonocoel is shallow and conceals only the bases of the telopodites (Figs 2K, 3).
Remarks. This new species shows several clear-cut apomorphies in gonopodal characters (see Diagnosis above), but on balance it fits quite well the scope of Physetoparia as outlined by Golovatch et al. (2018). Especially distinct similarities concern the sole congener that has a marked apicolateral outgrowth/lobe on the gonopodal coxa to protect a likewise well exposed telopodite: P. villiersi (Schubart, 1955). However, the gonotelopodite in the latter species is tripartite, including a finger-shaped solenomere, Figure 3. Physetoparia complexa sp. nov., gonopods of ♂ paratypes A, B left gonopod, lateral and ventrolateral views, respectively C right gonopod, ventrocaudal view D, E right gonopod, lateral and mesal views, respectively. Abbreviations: lo distolateral lobe of coxa, ab apicomesal branch/outgrowth of telopodite, tu tube/solenomere between lo and ab with a broad orifice (or) and a field of filaments (fi) at base. Scale bars: 0.05 mm.
while the coxal lobe is much smaller and less conspicuous (Schubart 1955). In addition, both these species compared come from the same area, the Nimba Mountains which are shared by Liberia, Guinea and Côte d'Ivoire.
As reiterated recently (Golovatch et al. 2018), this genus was first proposed as a nomen nudum (Cook 1896a), but then properly typified (Cook 1896b). The sole useful information contained in the original description of B. claviger, which was accompanied by no illustrations, concerns its small size (7 mm long, 1 mm wide), typically micropolydesmid facies (small paraterga, large and clubbed tergal setae arranged in three transverse rows etc.), strongly enlarged gonocoxae that fully conceal the telopodites and, above all, ♂ legs 2, especially their tibiae, greatly enlarged compared to others (Cook 1896b). No number of body segments has been given.
Below we put on record a new Bactrodesmus coming from the Guinean portion of the Nimba Mountains. This allows us to unequivocally clarify the identity of the genus and provide a new diagnosis.
Diagnosis. At least ♂ tibiae 2, as well as both gonopodal coxae and gonocoel hypertrophied, telopodites being strongly sunken and their distal outgrowths remaining nearly fully concealed inside gonocoel. Only one prominent, basal fold/branch (bb = sp) present, albeit fully concealed as well; a simple and short solenomere branch (sl) protected by bb mesally and by a clearly 2-segmented lateral part laterally.
Remark. This genus is presumably among the most advanced representatives of Afrotropical Trichopolydesmidae in showing several autapomorphies. Diagnosis. Differs from both other species of the genus by ♂ legs 1-3 being clearly enlarged and modified, vs. ♂ legs 2 or 2 and 3, from B. bicornis also by three (vs. two) transverse rows of tergal setae and the collum which is narrower than the head, from B. claviger by the considerably larger body.

Bactrodesmus grandis
Name. To emphasize the relatively large body and clearly enlarged ♂ legs 1-3; adjective.
Sterna wide, unmodified, setose. Legs rather long and slender, ca 1.3-1.4 (♂) or 1.1-1.2 times (♀) as long as midbody height; in length, tarsus > femur > prefemur > coxa = postfemur = tibia. Tarsal brushes present only on ♂ legs 1 and 2; ♂ legs 1-3 conspicuously enlarged (Fig. 4I): legs 1 (Fig. 4J) with increasingly inflated pretarsal podomeres; legs 2 ( Fig. 4K, L) with each coxa caudally supplied with what seems to be a gland whose wide orifice is surrounded by a whorl of setae while the interior carries bundles of abundant, very long, sharp, distally entangled filaments; tibiae 2 particularly strongly swollen, while tarsi 2 somewhat shortened, dorsally flattened and spoon-shaped; legs 3 ( Fig. 4K, M) resembling legs 1, but their prefemora and femora especially densely setose ventrally. Gonopods (Fig. 5) complex, with particularly strongly enlarged, globose and nearly smooth coxae (cx), both forming a very deep gonocoel, both clearly rimmed apically and with 2+2 especially strong setae mediobasally near place of coxal fusion; one small rounded lobe each present on cx distolaterally (lol) and distomesally (lom); cannulae relatively small, as usual. Telopodites deeply sunken inside gonocoel, very poorly exposed beyond it, each starting with a setose funnel-shaped part (fu) marking the orifice for the cannula to enter and the beginning of a seminal groove, the latter quickly passing onto a short, stout, slightly curved, distad attenuating solenomere (sl) branch fully concealed inside gonocoel; basal part of telopodite extended mesally along fu into a distinct fold turning apically into a long, gently and regularly curved, laterad directed spine (sp); lateral part of telopodite divided distally by a clear-cut suture (su) into two sections, both being simple and stout slabs, but distal one bearing a meso-central membranous sac to protect sl tip.
Remarks. The size, external structures and gonopodal conformation of B. grandis sp. nov. match closely those as described and depicted for B. bicornis by Demange and Mauriès (1975). The latter species is 8.0 mm long and 1.5 mm wide. Its hypertrophied gonopodal coxa is likewise nearly smooth and shows two small distal lobes, lol and lom. The short spiniform solenomere (sl), the long mesobasal spine (sp) and the twosegmented lateral part of the gonotelopodite look much like, and are located similarly in B. grandis sp. nov. Unfortunately, even though the gonopodal structure of B. claviger remains unknown, the genus Bactrodesmus can presently be redefined (see above). (Porat, 1894), comb. nov. Fig. 1D Polydesmus parvulus Porat, 1894: 31 (original description).

Type material. Syntypes 2 ♀ (NHRM-GULI000069465), Kamerun, Yngve Sjöstedt leg.
Remarks. Porat (1894) described this species, based on two syntypes deriving from an unspecified locality in Cameroon. We have revised both syntypes and found them to be adult females, one incomplete, the other one complete and with 20 segments (Fig. 1D). Since Cameroon appears to support solely species of the trichopolydesmid genus Hemisphaeroparia (24 at the moment), we tentatively transfer the above species to Hemisphaeroparia, comb. nov., even though the spiracles located next to coxa 1 or 2 are not enlarged (Fig. 1D). Characteristically enlarged spiracles 1 appear to be restricted to far from all species of Hemisphaeroparia (see below under H. spiniger). We doubt though that the identity of this enigmatic species will ever be properly established, as superficially the females of most species of Trichopolydesmidae look very much alike. Only the everted vulvae of one of the syntypes might be helpful in the future, but first their comparative study must be accomplished.  Remarks. The new samples fully agree with the original description (Golovatch et al. 2018) and are again illustrated not only to confirm the species' identity (Figs 6, 7), including the unique, conspicuous, epicranial bundles of long filaments on the ♂ head (Fig. 6D, J), but also to note the presence of a marked ventrobasal process on each ♂ prefemur 1 (Fig. 6L), which is much like the one observed in H. avis sp. nov. Remarks. The new samples fully agree with the original description (Golovatch et al. 2018) and are again illustrated to confirm the species' identity (Figs 8,9), including the remarkably enlarged spiracles 1.
The new locality, Mfou, lies quite close to the type one, campus of University Yaounde 1, both in the Central Region of Cameroon. Moreover, because both known localities/habitats represent artificial palm or cocoa plantations, H. spiniger could have been introduced there from some native woodlands still to be revealed or already vanished. Diagnosis. Differs from all other species of the genus by the presence of only 19 segments in both sexes, coupled with a distinct, central, setose pit with two paramedian pores at the bottom in the ♂ epicranium, and the particularly long, falcate, fully exposed branch/process ab on the gonopodal telopodite.

Hemisphaeroparia longibrachiata
Name. To emphasize the particularly long branch/process ab on the gonopodal telopodite; adjective in feminine gender.
Remarks. Mfou, the type locality of Hemisphaeroparia avis sp. nov., is shared with as many as further two congeners, H. spiniger and H. falcata.
Remarks. This genus is bound to remain dubious until a male topotypic sample from Fernando Po becomes available for study. The only other trichopolydesmid known from Fernando Po is Dendrobrachypus pusillus Verhoeff, 1941 (= Mecistoparia pusilla), which is only 5.0-5.5 mm long (Verhoeff 1941). Mauriès and Heymer (1996) tentatively synonymized Trichozonus with Physetoparia.

Discussion
Interestingly, based on the gonopodal conformations alone, all Afrotropical Trichopolydesmidae seem to represent a single lineage characterized by basically rounded, lensshaped, oblong, relatively small gonotelopodites more or less deeply sunken into a gonocoel and showing, unlike the bulk of Euro-Mediterranean confamilial members (30 species in 17 genera, see Vagalinski et al. (2019)), no transversely oriented bases. The various outgrowths (usually 1-3) of the telopodites, if any, are typically not erect, but curved and directed caudomesad, while the solenomeres, if any, are mostly simple, short, fully mesal processes or lobes. In addition, most species in life tend to show different tinges of red, but are quick to fade in alcohol. Only one genus and species, Simplogonopus rubellus (Attems, 1902), also reddish in vivo, seems to be of the Afrotropical stock, but it occurs beyond tropical Africa. It has been recorded only from Crete, the Aegean islands of Kythnos and Chios, and northeastern Bulgaria (Vagalinski et al. 2019). Among the possible reasons to explain such a distribution, the following have been considered: (1) a palaeorelict survivor, (2) a human-caused introduction, and (3) recent migration. A combination of reasons cannot be excluded either (Vagalinski et al. 2019).
Previous knowledge of the trichopolydesmid fauna of Cameroon (Golovatch et al. 2018) seems to point to two interesting observations. Cameroon presently appears to be the country in Africa best known with regard to Trichopolydesmidae diversity, even though its trichopolydesmid fauna seems to be surprisingly monotonous, represented by species (16 of 26) of a single large genus, Hemisphaeroparia, which ranges from Guinea in the west to Uganda in the east. This has also permitted us to provisionally assign an old species described from Cameroon to that genus as well. The second observation is that there tend to be as many species as localities, meaning that each species has been encountered in a single place. Localities that support two species are rather exceptional (Golovatch et al. 2018).
Our present contribution partly disproves the latter observation, since two already described species have been found more widespread and occurring at least at localities other than the type ones. Moreover, the present paper reveals that one and the same locality can harbour as many as three congeners! It is quite clear that the diversity of Trichopolydesmidae in tropical Africa, despite all efforts, both past and present, remains grossly understudied. Many new taxa and records are undoubtedly still ahead, but we believe we have a sufficiently solid foundation to continue.