A new species of Pionothele from Gobabeb, Namibia (Araneae, Mygalomorphae, Nemesiidae)

Abstract The mygalomorph spider genus Pionothele Purcell, 1902 comprises two nominal species known only from South Africa. We describe here a new species, Pionothelegobabebsp. n., from Namibia. This new species is currently only known from a very restricted area in the Namib Desert of western Namibia.


Introduction
The nemesiid genus Pionothele Purcell, 1902 is a poorly known taxon comprising only two species described from southwestern South Africa. In Zonstein's (2016) review of the genus, he redescribed and illustrated P. straminea Purcell, 1902 and described a second, new species P. capensis Zonstein, 2016. Similarities between female specimens of Pionothele and those in the genus Spiroctenus Simon 1889a suggest that some species described as the latter may be misidentified as the former (Zonstein 2016); consequently, Pionothele may be more widespread and diverse than is currently known. We describe herein a new species, Pionothele gobabeb sp. n., from the Namib Desert in central western Namibia; the type locality at the Gobabeb Research & Training Center is about120 km southeast of the Atlantic coastal city of Walvis Bay. The description of this new species extends the distribution of Pionothele significantly northward, indicating that the genus may contain considerable undescribed diversity, particularly in the intervening areas.
Habitat and ecology. Fifteen males were collected in pitfall traps after a rain event at Gobabeb; specimens were observed along interdune and gravel plain transects -two of six habitats monitored by long-term pitfall trapping (Henschel et al. 2003). Gobabeb lies adjacent to the Kuiseb River, an ephemeral drainage where the northern terminus of the Namib Sand Sea abuts the gravel plains of the Central Namib. Here dune, riparian, and gravel plain habitats occur in close proximity. Figure 1 illustrates the Gobabeb collecting locality. The single female specimen was collected from a subterranean burrow on a sandy slope. All nominal species of Pionothele have been collected from dune ecosystems (or close proximity thereof ).
Species concept applied. This new species of Pionothele is delineated using a traditional morphological species concept wherein species are defined as those populations with qualitative phenotypic characteristics that differ in a discrete manner from other populations or groups.

Abbreviations, materials and methods
Institutional and quantitative morphological abbreviations used in this paper are defined as follows:

BME
Bohart Museum of Entomology, Davis, California.

NMN
National Museum of Namibia, Windhoek, Namibia CAS California Academy of Sciences, San Francisco, California.

Quantitative morphological features
The following features are explicitly defined and illustrated in Bond (2012): ANTd number of teeth on the anterior margin of cheliceral fang furrow. Cl, Cw carapace length and width. Carapace length taken along the midline dorsal-most posterior position to the anterofrontal edge of the carapace (chelicerae are not included in length). Carapace width taken at the widest point. AME, ALE, PME, PLE anterior median, anterior lateral, posterior median, and posterior lateral eyes, respectively. LBl, LBw labium length and width taken from the longest and widest points, respectively. PTl, PTw male palpal tibia length and width. Bl palpal bulb length from embolus tip to the bulb base, taken in the ventral plane at its longest point.

PTLs, TBs
number of female prolateral patella and tibial spines leg III. STRl, STRw sternum length and width. Sternum length from the base of the labium to its most posterior point. Width taken across the widest point, usually between legs II and III. PLS posterior lateral spinneret TSrd, TSp, TSr number of tibiaI spines on the distal most retrolateral, prolateral, and midline retrolateral positions.

ITC
inferior tarsal claw

Measurement, characterization, and illustration of morphological features
Format, descriptors, and morphological features measured/examined follows closely Bond (2012). Unique voucher numbers were assigned to all specimens (alphanumeric designations beginning with NMB); these data were added to each vial and can be used to cross-reference all images, measurements, and locality data. All measurements are given in millimeters and were made with a Leica MC205 dissecting microscope equipped with the Leica Analysis Suite Software. Lengths of leg articles were taken from the mid-proximal point of the articulation to the mid-distal point of the article (sensu Bond 2012, figs 11-16). Leg I and Leg IV article measurements are listed in the species description in the following order: femur, patella, tibia, metatarsus, tarsus. Carapace and leg coloration are described semi-quantitatively using Munsell® Color Charts (Windsor, NY) and are given using the color name and color notation (hue value/chroma). Digital images of specimens were made using a BKPlus Digital Imaging System (Dun Inc. TM , Richmond, VA) where images were recorded at multiple focal planes and then assembled into a single focused image using Helicon Focus (Helicon Soft, Ltd., Ukraine). The female genital region was removed from the abdominal wall and tissues dissolved using trypsin; spermathecae were examined and photographed in the manner described above. Following Bond (2012), habitus illustrations were constructed from whole body images that were bisected, copied, and reflected in Adobe Photoshop (Adobe Systems, Inc.) to produce a roughly symmetrical image; the actual raw images are available upon request from the first author. Unless otherwise stated, scale bars = 1.0 mm.

Locality data and georeferencing
Latitude and longitude for all collecting localities were recorded in the field using a Garmin Global Positioning System receiver (Garmin International Ltd., Olathe, KS) using WGS84 map datum. Etymology. The specific epithet is a noun taken in apposition and is in reference to the type locality.

Taxonomy
Diagnosis. Male and female specimens (Figs 2-4) can be differentiated from the other two described species of Pionothele by having posterior median eyes that are reduced in size (Fig. 7), nearly half the diameter of the posterior lateral eyes and much smaller than the anterior median eyes. Like P. capensis the male palpal tibia is more slender than in P. straminea but like the latter lacks spines (Fig. 8); leg I has more mid-retrolateral spines than P. capensis, with a single large mid-distal spine and only two proximal prolateral spines (Figs 5, 6). Males and females both are very light in coloration similar to that of P. straminea (Figs 2-4), noted by Raven (1985) as "faded," whereas the abdomen of P. capensis is pigmented and mottled. Spermathecal bulbs of P. gobabeb are moderately thin and sinuous whereas those illustrated for P. capensis are described as "wide and flattened" (Fig. 9); females also appear to have far fewer endite cuspules (25 vs 80).
Remarks. The female specimen described herein is from a locality some distance from where the male specimens and male holotype/paratypes were collected (formally designated as the type locality). As such we do not describe the female as a paratype so as not to confuse the type locality or the identity of the species if the female specimen is eventually discovered to be a different species -acknowledging that mygalomorph spiders are known to be highly endemic with considerable species crypsis (see Bond & Stockman 2008). Nevertheless, we are reasonably confident that these specimens are conspecifics given similarities in morphology (e.g., size of the PMEs), habitat, and an explicit morphological species concept (applied herein).
Additional material examined. Male specimens (12) collected in pitfall trips in vicinity of the type locality at Gobabeb, deposited in the BME. Single female specimen (NMB012_001) from the Erongo Region, Namibia, in vicinity of Intersection C39 and Huab River, -20.36035 14.19186898, coll. J. Bond 19.ix.2013, deposited in BME.
Distribution. Known only from the Erongo Region, Namibia.