On the Afrotropical genus Holmelgonia ( Araneae , Linyphiidae ) , with the description of three new species from the Albertine Rift

Three new species of Holmelgonia were found in the mountain forest of Kibira National Park in Burundi: H. afromontana sp. nov. (♂♀), H. bosnasutus sp. nov. (♂♀) and H. disconveniens sp. nov. (♂). A key to the males in the genus, now containing 17 species, is provided.


Introduction
Linyphidae have been popular among students of Afrotropical spiders and fi gure among the better known families of the continent, as far as the species living in the leaf litter layer is concerned.The interest in the family doubtlessly originated in the expertise several taxonomists had acquired in Europe, where the family Linyphiidae is by far the most speciose.Mainly Bosmans, Denis, Holm, Jocqué, Miller, Russell-Smith and Scharff all contributed to a great extent to the knowledge of the family thanks to the experience they had obtained by studying the European linyphiids.By the end of the last century, their extensive studies had yielded enough information about the family to result in an interactive key to the genera (Seyfulina & Jocqué 2007) and to allow generalisations about the distribution of the family, such as for instance the abundance of montane species (Scharff 1990(Scharff , 1992(Scharff , 1993) ) as compared to the paucity of the family in African lowland habitats and the small size of Afrotropical litter inhabiting linyphiids (Jocqué et al. 2013).
More recently, the fauna of the canopy yielded a high number of unknown linyphiid taxa (see Seyfulina & Jocqué 2009).Although the interest in Afrotropical linyphiids has apparently dwindled, the recent study by Frick & Scharff (2013) proves that the interest in Afrotropical linyphiids still slumbers.
The present study aims to stimulate renewed interest in African linyphiids and is the fi rst of a series of papers on linyphiids from the southern part of the Albertine Rift, a mountain range with a particularly diverse fauna (Nzigidahera & Jocqué 2009;Jocqué et al. 2013).It provides an overview of the endemic Afrotropical genus Holmelgonia Jocqué & Scharff, 2007.The genus, originally described by Holm (1962) as Elgonella, received the replacement name Elgonia Platnick (1986), but eventually became Holmelgonia since Elgonia also turned out to be a homonym (Jocqué & Scharff 2007).
The genus Holmelgonia contains 14 species (Platnick 2013) and has a wide distribution (see Fig. 1) ranging from Côte d'Ivoire in the west to Kenya and Mozambique in the east.Although most species live at high altitude and have small endemic ranges (Jocqué & Scharff 1986;Scharff 1993), some of them (e.g., H. holmi Miller, 1970;H. brachystegiae Jocqué, 1981) have a wide distribution at midaltitude.
Here we describe three new species from Burundi and provide a key to all the species for which males have been described.
The collections from which the type material of the new species originates are the result of an extensive sampling campaign carried out by the fi rst author in protected areas of Burundi during three periods in 2003, 2005 and 2008.They covered altitudinal gradients between 1970 m and 2650 m above sea level (asl).The discovery emphasizes the biodiversity of the Albertine Rift spider fauna with high numbers of species in many spider groups (Nzigidahera & Jocqué 2009).

Material and methods
The specimens were collected by the fi rst author in the afromontane forest of Kibira.Primary types are deposited in the Musée Royal de l'Afrique Centrale, Tervuren, Belgium (MRAC), whereas paratypes are divided among MRAC and the Institut National pour l'Environnement et la Conservation de la Nature, Bujumbura, Burundi (INECN).Specimens were observed, drawn and measured with a WILD M 10 stereo microscope.Details of the epigyne and male palps were observed with a Zeiss Stemi 2000 strereo microscope.
Epigynes were detached from the abdomen, cleared with methyl salicylate and temporarily mounted in a mixture of methyl salicylate and cedukol for examination.The same method was used to observe details of the male palp.These structures were photographed with a Leica MZ16 stereo microscope and subject to automontage with the Syncroscopy software.All measurements are in mm.As with the illustrations, they were taken from the holotype and paratypes unless stated otherwise.Coordinates are in decimal format.

Diagnosis
The generic defi nition is wide, as the original diagnosis by Holm (1962) had to be enlarged by Jocqué & Scharff (1986) to accommodate the species from Tanzanian mountain areas.The genus is characterized by the absence of cheliceral stridulating ridges (Figs 2-3); the presence of a double ventral row of setae on the femora; the long tibial spines, two to three times as long as the diameter of the segment; tibia I-IV with 2, 2, 1 and 1 spine, respectively; TMI between 0.32 and 0.7; males lack a cephalic lobe; the palpal tibia dorsally produced into a dorsal process 7).

Diagnosis
The male is characterized by the dorsal tibial apophysis, which is smoothly rounded at the extremity and has a ventral concavity provided with a short, sharp, tooth-shaped excrescence inside.Proximal and distal arms of the paracymbium with short setae, distal arm strongly sclerotized and curved at the tip.The female is recognized by details of the epigyne of which the central depression and the kidneyshaped spermathecae are the most characteristic.

Etymology
The specifi c name 'afromontana' refers to the high altitude habitat in which the species was collected.30).Fairly large ventral plate broadly indented in front, posterior margin slightly procurved.
Copulatory ducts originate from centre near posterior margin, entering spermathecae near lateral margin; spermathecae large, kidney-shaped, with transverse long axis.

Variation
Carapace colour may vary from medium brown to yellowish grey.

Distribution
Known only from the type locality (Fig. 1).

Diagnosis
The male is characterized by the sharply pointed dorsal tibial apophysis with undulated margin, each undulation provided with a hair, combined with the broad prolateral apophysis, the broad proximal arm and smoothly rounded tip of the distal arm of the paracymbium.Females are recognized by the shape of the epigyne, provided with two holes clearly visible and opening in the posterior margin.

Etymology
The specifi c name 'bosnasutus' refers to the shape of the epigyne which is reminscent of a cow's nose.
CEPHALOTHORAX.Carapace greyish brown with black striae radiating from fovea; with pale area behind posterior eyes, followed by rectangular spot from which two striae run towards the PLE.Chelicerae coloured as carapace, retromargin with 5 teeth; promargin with 5 small teeth.Clypeus 2. PALP (Figs 6,9,(30)(31)(32)(33). Retrolateral tibial apophysis with sharp tip and undulated lateral margins, each undulation provided with a hair; laterally with short, broad prolateral apophysis with blunt tip.Paracymbium with broad proximal arm and distal arm with smoothly rounded tip.Proximal part of tegulum with ventrolateral, oblique grooves.Embolic division with short curved embolus, long sharp ventral appendage, sinuous, frontal appendage with sharp tip and long, broad, rounded dorsal appendage.

Distribution
Known only from the type locality, Mt Musumba in Kibira National Park (Fig. 1).

Diagnosis
The male is characterized by the triangular dorsal tibial apophysis, with a tooth at the tip and sinuous prolateral margin, by the fairly large, sharp, sclerotized prolateral apophysis, and by the paracymbium without hairs, its distal arm with a well delimited knob.

Etymology
The specifi c name 'disconveniens' refers to the contrasting tinge of dark body and pale legs.

Distribution
Known only from the type locality (Fig. 1).

Discussion
Linyphiidae are a striking example of a family in which genera have been erected based on secondary sexual characters that appear to be species specifi c.This phenomenon was discussed in Jocqué et al. (2013), who argued that genera in some families are particularly diffi cult to defi ne when they contain so-called 'templates' (as defi ned by Jocqué & Bosselaers 2011), lacking clear somatic autapomorphies.The defi nition of Holmelgonia is no exception to this: apart from the absence of stridulating fi les on the chelicerae, no somatic characters could be found to defi ne it.Even the chaetotaxy, and more specifi cally the position of the metatarsal trichobothria, varies to an extent that is unusual in erigonine genera.The genus has therefore to be defi ned on the base of features of the secondary genitalia.The palp has a tibia with a dorsal process and the ED is rather complex, with several protuberances.Yet, in two of the species described here the ED is fairly simple.The latter feature, however, is not restricted to Holmelgonia and can be found in many genera in the Erigoninae.It thus remains questionable whether the species attributed to Holmelgonia really do constitute a natural group.
This study is a result of the intense sampling of ground spiders carried out in the forest ecosystems of western Burundi during several years (2003, 2005 and 2008).The three species described here were only found in the mountain forest of Kibira National Park.Holmelgonia bosnasutus sp.nov.occupies a wide altitudinal gradient, ranging from 2100 to 2650 m.The species H. afromontana sp.nov.and H. disconveniens sp.nov.are confi ned to a narrower altitudinal zone between 2100 and 2352 m.
This study shows again that the Albertine Rift in Central Africa has only been superfi cially explored with regard to its spider fauna.This was already clear with the discovery of species swarms in the Gnaphosidae, in which the genera Zelotibia Russell-Smith & Murphy, 2005 (20 species) and Zelowan Murphy & Russell-Smith, 2010 (18 species) were found to have radiated in that mountain range (Russell-Smith & Murphy 2005;Murphy & Russell-Smith 2010;Nzigidahera & Jocqué 2009).Further studies in preparation show that similar radiations can be expected in other genera of the Linyphiidae and in other families such as the Tetragnathidae, particularly in ground-living genera that have lost the web-building habit.There is a considerable urgency to describe the fauna in this region, where human populations are expanding rapidly and deforestation is consequently very intense.

Fig. 1 .
Fig. 1.Presently known distribution of Holmelgonia Jocqué & Scharff, 2007.Large arrow indicates Kibira National Park, type locality of the species described in this paper.
Figs 34, 40).With two holes at posterior margin, resembling the shape of a cow's nose.Copulatory ducts short, curved, originating from triangular atrium near posterior margin; entering spermathecae near lateral margin, spermathecae oval, longest axis longitudinal.
Oval, greyish black, with faint central dark brown band and small pale points, with six transverse pale chevrons in posterior half.Spinnerets yellowish grey, conical.