A mountain of millipedes II: The genus Aquattuor Frederiksen, 2013 – five new species from the Udzungwa Mountains and one from Mt. Kilimanjaro, Tanzania (Diplopoda, Spirostreptida, Odontopygidae)

The genus Aquattuor Frederiksen, 2013 is revised. A. denticulatus Frederiksen, 2013 (type species) from the East Usambara Mts, Tanzania, is redescribed, and six new species are described: A. claudiahempae sp. nov. from Mt. Kilimanjaro, Tanzania, and five species from the Udzungwa Mts, Tanzania: A. longipala Enghoff sp. nov., A. major Enghoff sp. nov., A. stereosathe Enghoff sp. nov., A. submajor Enghoff sp. nov., and A. udzungwensis Enghoff sp. nov.


Introduction
This is the second in a series of articles about the millipedes, especially the family Odontopygidae, of the Udzungwa Mountains, Tanzania.For general information on the Odontopygidae and the Udzungwa Mountains, see the first paper in the series (Enghoff 2014).The present article, although not numbered as such, also forms a sequel to our previous papers on the odontopygids of East Africa (Frederiksen 2013a(Frederiksen , 2013b;;Frederiksen & Enghoff 2012, 2015).
The genus Aquattuor was described by Frederiksen (2013b) for a relatively small odontopygid from the East Usambara Mountains, Tanzania.The genus, which has remained monotypic until now, is characterized by a slender, whiplike gonopodal solenomere and a simple telomere, combined with a unique structure of the metazonital limbus which consists of large, rectangular, easily detached flaps.
Collecting activities in the Udzungwa Mountains by the NGO Frontier Tanzania and by staff and students from the University of Copenhagen (cf.Enghoff 2014) have resulted in a considerable amount of material containing several new species of Aquattuor.At the same time, collections made in the framework of The KiLi Project (https://www.kilimanjaro.biozentrum.uni-wuerzburg.de/),sponsored by the German Research Foundation (cf.Frederiksen & Enghoff 2015), have procured several samples of still another new species.
In the present article we describe six new species of Aquattuor, re-describe the type species, A. denticulatus Frederiksen, 2013, and provide an updated definition of the genus as well as a key to its species.

Material and methods
For reasons explained by Enghoff (2014), only adult males were considered.A total of 85 adult Aquattuor males were examined.All specimens are stored in 70% ethanol and are kept in the Natural History Museum of Denmark, University of Copenhagen (ZMUC).Specimens were examined in 75% ethanol under a stereo microscope.Numbers of podous rings were counted and midbody vertical diameter measured on complete specimens.Body parts for scanning electron microscopy (SEM) were transferred to 96% ethanol, then to acetone, air-dried, mounted on aluminium stubs or on triangles of flexible aluminium tape and in turn mounted on stubs, coated with platinum/palladium and studied in a JEOL JSM-6335F scanning electron microscope.
A general description of the genus is provided.The species diagnoses include, inter alia, information on the number of body rings and body diameter.Although it cannot be excluded that specimens falling outside the indicated ranges may be found, this information nevertheless helps to characterize each species.Gonopod terminology is as far as possible as in Enghoff (2014).Because of the great uniformity of Aquattuor species, and because size information and gonopod details are included in the diagnosis, the traditional "Description" paragraph has been replaced by a short note on colouration.Adding more would be redundant.
For the species from the Udzungwa Mts, species of Aquattuor and Chaleponcus (cf.Enghoff 2014) occurring in the same samples and localities are listed under "coexisting species".

Diagnosis
A genus of Odontopygidae Prionopetalini in which the gonopodal proplica is apically expanded into a distal 'palette', the metaplica has an oblique flange, the solenomere is simple, thin and whiplike, the telomere terminates in a long, curved gutter-like to tubular part, and the limbus of the body rings consists of large, rectangular, easily detached flaps.

Etymology
The genus owes its name to the unique limbus flaps which resemble tiny sheets of paper in the standard A4 format.

Description
This description only applies to males and, as far as non-gonopodal characters are concerned, only includes a selection.
Colour.Colours of specimens from Udzungwa and East Usambara Mountains all partly or completely faded, leaving only newly collected specimens from Mt. Kilimanjaro with fresh colour (Fig. 1).Light mid-dorsal longitudinal stripe or traces thereof sometimes present, even on faded specimens.limBus.Consisting of relatively large (c.0.04 × 0.06 mm) rectangular flaps which are easily detached (Fig. 3D-E).
telson (Fig. 3B-C).Preanal ring with wrinkled / coriaceous sculpture dorsally.Anal valves with wrinkled / coriaceous sculpture, with a pronounced dorsal denticle and a smaller ventral one, denticles well set off from rest of valve rather than just being "sharp corners".Each valve with three setae.Free margin ("lip") of anal valves raised and provided with three small tubercles on which the setae are borne.
telomere.At base expanded into a complicated basal telomeral lamella (btl) obscuring origin of solenomere (Fig. 5D).Main part of telomere consisting of a long, narrow lamella folded into a more or less narrow gutter, sometimes even tube-like in distalmost part; gutter/tube describing a 90°-360° curve, usually in almost one plane, but sometimes (A.stereosathe Enghoff sp.nov.) clearly in three dimensions (note: this applies to preserved specimens).Posterior margin of gutter expanded into mesal-posterior lamella (mpl) (e.g., Fig. 5D).Tip of telomere variable: margins smooth or denticulate-laciniate, internal surface of gutter more or less microspiculate (e.g., Fig. 6C-D).

Distribution
Species of Aquattuor are so far known only from Tanzania.They have been found in several mountain blocks belonging to the Eastern Arc Mts (Burgess et al. 2007): Udzungwa (5 species), Nguru (1 species), Rubeho (1 species) and East Usambara (1 species).One further species has been found on Mt.Kilimanjaro.For an overview, see Figs 12-13.

Notes on identification
The species of Aquattuor are all quite similar, even in gonopod structure.In this respect, they form a contrast to the previously treated (much larger) species-swarm centred in the Udzungwa Mts., i.e., the Chaleponcus dabagaensis-group (Enghoff 2014), in which gonopods are highly diverse.Differences between Aquattuor species concern body size (Fig. 2), details of the outline of the gonopod coxa, the curvature of the telomere, the development of the posterior margin of the telomere, and the armature of the telomere tip.

Similar genera
By far the most diagnostic character of Aquattuor is the large (sub)rectangular-lobed limbus.Subrectangular limbus lobes do occur in certain other odontopygid genera, e.g., Allantogonus Attems, 1912(Kraus 1960: fig. 5) and Syndesmogenus Attems, 1909(Kraus 1966: figs 97-99), but in these genera, the lobes are much smaller and are not prone to detachment.The gonopods of Aquattuor, with their long, whip-like solenomere and slender telomere, superficially resemble those of Allantogonus (Kraus 1960:   figs 7, 11, 17) and Lamelloramus Frederiksen, 2013(Frederiksen 2013: figs 5, 9).However, the coxal apex in Allantogonus is folded basad over the anterior side; the metaplical flange of Lamelloramus is situated completely differently on the median side, and the telomere is either strongly curling up or looping in these genera.The limbus is completely different from that of Aquattuor in both.

Etymology
The name is an artificial Latin adjective meaning "below major" and refers to 1) the smaller size of this species compared to A. major Enghoff sp.nov.and 2) the fact that this species occurs at lower altitudes than A. major Enghoff sp.nov.

Colouration
After 33 years in alcohol faded, only some darker markings on head and collum left.No traces of a middorsal stripe.

Distribution and habitat
Known only from Mwanihana FR.Altitudinal range: 1000-1250 m asl.

Coexisting species
Aquattuor major Enghoff sp.nov.and Chaleponcus mwanihanensis Enghoff, 2014 occur in the same area, but only at higher altitudes.

Etymology
The name is a Latin adjective meaning "larger" and refers of the larger size of this species, compared to its congeners.

Colouration
After 31-33 years in alcohol faded, only some darker markings on head and collum left.No traces of a mid-dorsal stripe.

Distribution and habitat
Known only from Mwanihana FR.Altitudinal range: 1650-1850 m asl.Habitat: montane rain forest.

Coexisting species
Aquattuor submajor Enghoff sp.nov.and Chaleponcus mwanihanensis Enghoff, 2014 occur in the same area, the former, however, only at lower altitudes.

Etymology
The name is a Latin noun, here in apposition, composed of longi-(long) and pala (palette), and refers to the shape of the apical part of the gonopod coxa.

Colouration
After 15 years in alcohol still with a clear mid-dorsal, light longitudinal band, flanked by darker areas.Head and collum with some dark markings.

Distribution and habitat
Known only from West Kilombero Scarp FR.Altitudinal range: 1390-1410 m.Habitat: montane forest.

Distribution and habitat
Known from Udzungwa Scarp FR and from West Kilombero Scarp FR.Altitudinal range: 750-1410 m.Habitat: lowland rain forest and montane rain forest.

Etymology
The name is a Greek noun, here in apposition, composed of stereo-, which refers to the threedimensionality of the curvature of the telomere, and sathe, literally meaning "penis", here referring to the telomere.

Colouration
After 25-31 years in alcohol still with a clear mid-dorsal, light longitudinal band, flanked by darker areas.Head and collum with some dark markings.

Species from areas other than the Udzungwa Mountains
In addition to the Udzungwa Mts, species of Aquattuor have been collected in the East Usambara, Nguru and Rubeho Mts, which all belong to the Eastern Arc Mountains (Burgess et al. 2007), and on Mt.Kilimanjaro, a much younger, volcanic mountain (Nonnotte et al. 2008).

Etymology
The name is a feminine noun in the genitive, referring to Claudia Hemp, Würzburg, project leader of the DFG research group Kilimanjaro, in acknowledgement of her great support.

Colouration
Mostly brown, darker on the dorsal side, with a clear mid-dorsal, yellow longitudinal band, lighter yellowish on the ventral side; legs, head, collum and telson mostly brown (Fig. 1).

Distribution and habitat
Known only from Mt. Kilimanjaro in habitats disturbed by human activities: chagga homegardens (Soini 2005) and coffee plantations.The grassland plot where one specimen was collected is used for fodder harvest and is thus also under human influence.Altitudinal range: 1169-1345 m asl.

Colouration
After 35-40 years in alcohol, colouration faded, yellowish brown with no clear markings.

Distribution and habitat
Known only from the East Usambara Mts.Altitudinal range: 500-1000 m asl.Habitat: lower montane forest.

Remarks
The characteristic limbus places this specimen in Aquattuor, but in the absence of a male, the identity of the species remains obscure.The Nguru Mts are located roughly midway between the Udzungwa and the Usambara Mts.

Key to species of Aquattuor Frederiksen, 2013
The key is based on adult males.The diameter and number of podous rings are not absolute charactersnewly collected specimens may fall outside the ranges (and because of the positive correlation between number of rings and diameter, if a specimens falls outside in one parameter, it is likely to fall outside in the other as well).Differences between species are subtle, and specimens should be carefully compared with the diagnoses and illustrations.Specimens collected in new localities are likely to represent new species.

Discussion
Although by far most of the available material of Aquattuor species is from the Udzungwa Mts, the genus has also been found in the East Usambara, Nguru and Rubeho Mts, all part of the Eastern Arc  (Figs 12-13), and it is quite likely that Aquattuor will be discovered elsewhere in this ancient mountain The occurrence of A. claudiahempae sp.nov. on Mt.Kilimanjaro appears to be an anomaly, and three lines of evidence suggest that this species may have been introduced into Mt.Kilimanjaro: 1) it occurs only in disturbed habitats, 2) one specimen which is virtually identical to A. claudiahempae sp.nov.has been found in the Rubeho Mts, 350 km from Mt. Kilimanjaro, and 3) A. claudiahempae sp.nov.was not collected during earlier explorations of Mt.Kilimanjaro, including the rather large-scale Sjöstedt Expedition (Attems 1909).

Fig. 2 .
Fig. 2. Body size (numbers of podous rings and midbody vertical diameter) in ♂♂ of species of Aquattuor Frederiksen, 2013.In cases of (almost) coinciding values, symbols have been slightly displaced horizontally.

Fig. 12 .
Fig. 12. Map of part of Tanzania showing the mountains where Aquattuor species have been found.Based on Burgess et al. (2007: fig.1).

Fig. 13 .
Fig. 13.Map of the Udzungwa Mts showing the forest reserves where Aquattuor species have been found, and the epithets of the species found.Based on Marshall et al. (2010: fig.1).