On the genus Pachygnatha ( Araneae , Tetragnathidae ) in the Albertine Rift of Burundi , with the description of three new species

Three new species of Pachygnatha, P. bispiralis sp. nov., P. intermedia sp. nov. and P. ventricosa sp. nov., are described from forest areas in western Burundi. The presence of P. procincta Bosmans & Bosselaers, 1994 in Burundi confirms its very wide distribution spanning most of Africa. Pachygnatha appears to be an important element of the afromontane spider fauna.


Introduction
Twelve species of Pachygnatha Sundevall, 1823 are known from tropical africa (Platnick 2014).Bosmans & Bosselaers (1994) gave an excellent overview of this fauna and not only described several new species from cameroon but also redescribed all known species except one, P. africana Strand, 1906 for which the types could not be traced, doubtless because they have been destroyed during World War ii (renner 1988). of the twelve species, two are known from central africa, and more precisely from mountainous areas in the albertine rift: Pachygnatha kiwuana Strand, 1913, andPachygnatha ruanda Strand, 1913.During three years (2003,(2004)(2005)2008) of field work along altitudinal gradients (793 to 2650 m) in the afromontane forest of Kibira, miombo forest of rumonge and circum-guinean forest of Kigwena, four species of Pachygnatha have been found.only Pachygnatha procincta Bosmans & Bosselaers, 1994 has been previously described.it apparently has a wide distribution and was known from cameroon and Kenya.Three other species are here described as new.

Material and methods
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 female genitalia and male palps were observed with a zeiss Stemi 2000 strereo microscope.
Female genitalia 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.The distribution map for Pachygnatha procincta (Fig. 6) shows only one spot in Burundi: it covers both the adjacent collection sites Kibira and Kigwena mentioned in this paper and of which the former is the type locality of the three new species.

Diagnosis
Males are easily recognized by several unique features: the peculiar cymbium which is strongly narrowed at the mid-point, the very long conductor protruding beyond the cymbium, the tibia with a large ventrolateral apophysis and the very large, claw shaped, distal spur on the chelicerae.
abdoMen.Yellowish grey with irregular, connected dark grey spots in almost three longitudinal lines, mixed with silvery spots.Spinnerets pale yellow.palp.(Fig. 2a-B).Sclerotised tibial apophysis very broad, large blade-shape retrolaterally high, ventrally short.Paracymbium long, straight with some long hairs at the sharp, slightly curved tip.cymbium very broad at base, thin in middle and wider towards tip.embolus long, running along tegulum and beyond to tip of cymbium, supported by conductor.

Diagnosis
Males are recognized by details of the palp: the cymbium is unique in having a central membranous area dividing it into a proximal and a distal part, the latter provided with a short, thin prong; the paracymbium is broad at its base with a retrolateral swelling and a triangular prolateral extension, the distal part is slender and tapered to a point; the tibia has a well developed truncate dorsal apophysis.The female is recognized by the rectangular sclerotised areas in front and behind the genital opening.
P. intermedia sp.nov. is closely related to P. okuensis Bosmans & Bosselaers, 1994.The males share the distal paracymbial excavation, the shape of the cheliceral fang and the lozenge shaped paracymbium.
Both the latter differ in details of the shape: in P. intermedia the triangular extension of the cheliceral fang is much more pronounced and the distal prong of the paracymbium is much more slender and longer; the excavation of the cymbium is subdistal whereas it is at the distal tip of P. okuensis.The female has a cheliceral spur on the promargin of the chelicerae.With P. goedeli Bosmans & Bosselaers, 1994 it shares the paracymbium with long narrow distal extension and the small cymbial distal prong but details of these sclerites are clearly different.

Etymology
The specific name intermedia refers to shape of the paracymbium which is of median size in between the very broad paracymbium of Pachygnatha ventricosa sp.nov.and the narrow one of P. bispiralis sp.nov.MeasureMents.Total length 3.80, carapace 1.90 long, 1.60 wide.
CarapaCe.Brown, with prominent anterior part delimitated by dark brown lines converging in fovea in Y-shape.
sternuM.Brown, with a sharp sclerotised point at each end of the slightly concave anterior margin; intercoxal extensions present.
legs.Pale yellowish brown with some vague grey spots near femur-patella and tibia-metatarsus articulations; one dorsal distal spine on patellae; no further spines.
abdoMen.dorsum pale grey with irregular, connected dark grey spots in almost three longitudinal lines, raising a pale area in anterior part; venter pale grey with silvery spots in four longitudinal lines.Spinnerets yellowish grey.

Etymology
The specific name ventricosa refers to the inflated, belly-shaped lateral part of the paracymbium on the male palp.MeasureMents.Total length 3.47, carapace 1.67 long, 1.34 wide.

Holotype
CarapaCe.Pale brown, prominent anteriorly, with a mediodorsal longitudinal dark brown band and two lateral margin dark brown bands.
sternuM.Yellowish brown with a sharp sclerotised point at each end of the straight anterior margin; intercoxal sclerites present.Labium brown.legs.Yellowish brown; one thin slightly recurved dorsal distal spine on patellae; no further spines.
legs.With some vague grey spots on articulations of femora and patella and the tip of tibia; one spine on patella.external genitalia.5B). a simple, horizontal slit with an inferior part highly sclerotised laterally, superior one blade-shape and connected to inferior one by hyaline extension in two extremities; a sclerotised fold along the superior part.

Remarks
The specimen was compared to the holotype from cameroon (Mrac 202728) and to the specimens from two localities in Kenya (Mrac 111873, Mrac 112015), that were attributed to the same species by Bosmans & Bosselaers (1994).Reexamination confirms the close resemblance between all these specimens in which the males are characterized by the shape of the paracymbium.This sclerite has a very typical comma shaped bald retrolateral area.The cheliceral dentition of the specimens is virtually identical.The Burundian specimen has a slightly different colouration in the sense that it is paler and less orange than the other specimens.The presently known distribution is shown in Fig. 6.

Discussion
This study is a result of the intense sampling campaign of ground spiders carried out in the forest ecosystems of Western Burundi during several years (2003,2005,2008).Pachygnatha ventricosa sp.nov.was found only in the afromontane forest of the Kibira National Park whereas Pachygnatha bispiralis sp.nov.and P. intermedia sp.nov.were collected there and in the circum-guinean forest of Kigwena at lower altitude.according to our study, 4 species of Pachygnatha are found in this small part of the albertine rift which corroborates the conclusion of Nzigidahera & Jocqué (2009).They observed  (2005) found that no less than 19 species are known from the area.This is therefore the first African area for which there is evidence from the spider fauna that it deserves the epithet "hot spot".other recent papers on the fauna of the area pointing in the same direction are those on the gnaphosid Zelowan Murphy & russell-Smith, 2010 (Murphy & russell-Smith 2010), on zodariids (Nzigidahera & Jocqué 2010a, 2010b) and linyphiids (Nzigidahera & Jocqué 2014).These studies also suggest that the albertine rift is far from completely inventoried and several papers concerning its spider fauna are in preparation.
The genus Pachygnatha has a remarkable distribution on the african continent.all the species have been found above 1200 m (see Table 1) apart from a few specimens of the new species P. bispiralis and P. intermedia, which are common around 2000 m and higher but were also collected near 800 m.Pachygnatha thus appears to be a common element of the afromontane spider fauna but had not yet been recognized as such.Moreover, it is a typical case of a template genus with very stable somatic characters but with a large range of secondary sexual characters, more precisely of the male palp and the dentition of the chelicerae.a more extensive study of the genus may therefore yield insights into the evolution of secondary sexual characters and their link with biogeographical distribution.
National Park and Kigwena Nature reserve in Burundi.
).With rectangular sclerotised areas in front of and behind the genital opening.♂♂, 2 ♀♀, Kibira National Park, Rwegura Forest, 02.89435°S, 029.50078°E, forest with Maracanga neomildbreadiana and Xymalos monospora, 19Mar.2003,2223 m, pitfalls, B. Nzigidahera  Strand, 1913but the distal part of the paracymbium is much longer and well separated from the basal part in P. ventricosa sp.nov.Females are characterized by external genitalia with a sclerotised and transverse expansion of the upper lip forming a rectangular shape.
has two parts: a broad basal part, divided from the parallel-sided distal part by a deep, membranous indentation.This resembles that of P. bispiralis sp.nov., but the narrow central part of the cymbium is much longer and not membranous.in Pachygnatha intermedia sp.nov.there is a central membranous cymbial area but the shape of that sclerite is very different.This is somewhat similar to that of P. kiwuana