Review of the ant genus Nesomyrmex Wheeler , 1910 ( Hymenoptera , Formicidae , Myrmicinae ) from the Arabian Peninsula

In this study, we review the Arabian species of the ant genus Nesomyrmex Wheeler. We provide species reviews for the two previously known species, N. angulatus (Mayr, 1862) and N. humerosus (Emery, 1896) and describe a new species N. zaheri sp. n. from Yemen based on the worker caste. An illustrated key to the Arabian species of the genus and montage photos of all three species are provided.


Review of the ant genus Nesomyrmex
(Hymenoptera, Formicidae, Myrmicinae) from the Arabian Peninsula

Introduction
The myrmicine ant genus Nesomyrmex Wheeler, 1910 is distributed in the subtropical and tropical regions of the Neotropical, Afrotropical, and Malagasy Regions.With currently 80 valid species, the genus is comparatively species-rich (Bolton 2017).
In the last decade the taxonomy of the Old World fauna, especially the Afrotropical Region, has received much attention.Bolton (1982) and Snelling (1992) initially recognized ten Afrotropical species and subsequently Mbanyana and Robertson (2008) revising the South African taxa described 15 new species, increasing the number of species in this region to 25 species.Recently, Hita Garcia et al. (2017) reviewed the taxonomy of the genus for the Afrotropical Region proposing four species groups, and revising the N. angulatus species group, bringing the total number of species to 26.Recently, the Malagasy Nesomyrmex fauna was revised by Csősz andFisher (2015, 2016a, b, c, d).They divided the genus into five species groups and recognized 33 species, of which they described 29 as new.
Little taxonomic or biogeographical information is currently available for the Arabian Nesomyrmex, of which only two species are known.The wide-spread and common species, N. angulatus (Mayr 1862) has been recorded from the Kingdom of Saudi Arabia, Oman, and Yemen, whereas the rare N. humerosus (Emery, 1896) is only known from one collection from Yemen (e.g.Collingwood 1985, Collingwood and Agosti 1996, El-Hawagry et al. 2013, Borowiec 2014, Hita Garcia et al. 2017, Sharaf et al. 2017a).
While treating the Arabian species of Temnothorax Mayr, 1861 (Sharaf et al. 2017b), the first author examined a misidentified specimen in the King Saud University Museum of Arthropods (KSMA).Further study indicated that this specimen was not a Temnothorax but clearly represented an undescribed species of Nesomyrmex.In this study, we recognize this specimen as a new species and review the species from the Arabian Peninsula.We provide species accounts for the two previously known species and a detailed description for the new species N. zaheri sp.n..The erroneous record of Nesomyrmex denticulatus (Mayr, 1901) by El-Hawagry et al. (2016) is rectified here.The species is known only from South Africa and its distributional record from Arabian Peninsula is incorrect.Herein we present a first illustrated identification to the worker caste for the Arabian Peninsula, as well as montage images for all three species.

Material and methods
Morphological examinations were made using a Nikon SMZ 1500 stereo zoom microscope.The images of the type are available at AntWeb (https://www.antweb.org).General terminology for ant morphology is based on Bolton (1982Bolton ( , 1994)), and for the description of degrees of inclination of pilosity we follow Wilson (1955).Measurements and indices are presented as minimum and maximum values with arithmetic means in parentheses, and all measurements are expressed in mm to two decimal places.The following measurements and indices used in this study (see Fig. 1) follow Hita Garcia et al. (2017):

HL
Head length: maximum distance from the midpoint of the anterior clypeal margin to the midpoint of the posterior margin of head, measured in full-face view.Impressions on the anterior clypeal margin and the posterior head margin reduce head length.

HW
Head width: width of the head directly behind the eyes measured in full-face view.

SL
Scape length: maximum scape length excluding basal condyle and neck.

EL
Eye length: maximum diameter of compound eye measured in oblique lateral view.

PH
Pronotal height: maximum height of the pronotum measured in lateral view.

PW
Pronotal width: maximum width of the pronotum measured in dorsal view.

WL
Weber's length: diagonal length of the mesosoma in lateral view from the posteroventral margin of propodeal lobe to the anterior-most point of pronotal slope, excluding the neck.

PSL
Propodeal spine length: in dorsofrontal view the tip of the measured spine, its base, and the centre of the propodeal concavity between the spines must all be in focus.Using a dual-axis micrometre the spine length is measured from the tip of the spine to a virtual point at its base where the spine axis meets orthogonally with a line leading to the median point of the concavity.

PTH
Petiolar node height: maximum height of the petiolar node measured in lateral view from the highest (median) point of the node to the ventral outline.

Abbreviations
Throughout the text we abbreviate the castes in the following way: "w" for worker(s), "q" for queen, and "m" for male.
Comments.This species exhibits remarkable variability throughout its distributional range, most notably in the shape of the petiolar node (Bolton 1982, Hita Garcia et al. 2017), but it is also relatively variable in body size and eye size.It is likely that the material currently understood to be N. angulatus is actually a complex of cryptic species.However, in order to examine this question in detail it would be necessary to gather substantial material from throughout its whole distribution range from numerous museum collections.Despite that this is a highly desirable undertaking; it is outside the scope of the current study that focuses on the Arabian fauna only.OI 39;SI 83;CI 95;DMI 58;LMI 38; Distribution.Nesomyrmex humerosus is currently only known to occur in Kenya, Tanzania, and Yemen.Very little is known about the biology of the species.Rarely collected species seems to live on vegetation but has also been sampled from the ground (Hita Garcia et al. 2017).Comments.Nesomyrmex humerosus is the only member of the N. humerosus group and possesses an unusual character combination for an Afrotropical species due to its flat anterior clypeal margin, dentate pronotum, and barrel-shaped petiole.For more details see Hita Garcia et al. (2017).This species has been infrequently collected and is apparently known from four separate collections.More intensive sampling in East Africa and Yemen should yield more material.It is noteworthy that we were not able to examine any material of this species from Yemen and all our knowledge of the species is based on literature (Collingwood andAgosti 1996, Borowiec 2014).Diagnosis.The following character combination separates N. zaheri from the other Nesomyrmex species known from the Arabian Peninsula: third mandibular tooth relatively smaller and reduced; anterior clypeal lobe always conspicuously developed, convex and rounded, never with a small median triangular projection; pronotum anterodorsally without sharp, dentate corners; clypeus without median longitudinal carina; in profile mesosomal dorsum forming a single, uninterrupted flat surface without any trace of metanotal groove; petiole with very well developed node.
Waist segments and gaster.Petiolar peduncle moderate short; in profile petiolar node relatively high and narrowing from base to apex, around 1.2 times as high as long (LPeI 81); anterior and petiolar faces truncate; node in dorsal view weakly wider than long (DPeI 106) and denticulate; in profile postpetiole globular, about 1.8 times as high as long (LPpI 57); in dorsal view about twice as wide as long (DPpI 200); postpetiole in dorsal view around 1.3 times as wide as petiolar node (PPI 133).
Pilosity and pubescence.Head, mesosoma, waist segments and gaster dorsally with stout, erect, blunt, and moderately short pilosity; head laterally and ventrally with short appressed to decumbent pubescence; pubescence on mesosoma and waist segments sparse to absent; gastral tergites with short appressed to decumbent pubescence.
Coloration.Body uniformly light brown with head darker and the appendages lighter in colouration.
Distribution.At present the new species is only known from the type locality, which is located near the Indian Ocean in southwestern Yemen near Aden.Nothing is known about the biology or nesting behavior of the species.
Comments.The new species is clearly a member of the N. angulatus species group sensu Hita Garcia et al. (2017).It is the third species known from the Arabian Peninsula and can be well separated from the other two species by the characters given in the key.Nesomyrmex zaheri can be easily distinguished from N. humerosus.However, N. zaheri and N. angulatus are morphologically very similar and differ only by a few morphological characters.As noted above, N. zaheri differs from N. angulatus by the lack of a median clypeal carina and a much shorter third mandibular tooth.In addition, N. zaheri has a slightly wider (DPpI 200 vs. 154-188) and higher (LPpI 57 vs. 68-91) postpetiole.These measurements may be found to overlap if additional specimens of N. zaheri become available.It is possible that the holotype of N. zaheri may be a geographical variant of the widespread N. angulatus.However, we examined several hundred N. angulatus from throughout its recognized geographical distribution and all specimens possessed a median clypeal carina, a character, which is usually stable in ants.

Discussion
Nesomyrmex is broadly distributed throughout the Afrotropical and the Malagasy Regions (Fisher and Bolton 2016).Of the two species treated here, N. angulatus is widespread but predominantly Afrotropical and N. humerosus has been reported from Kenya and Tanzania (Hita Garcia et al. 2017).Despite being supposedly endemic to Yemen, the new species is a member of the Afrotropical N. angulatus species group.Consequently, all three species treated in this study confirm a strong Afrotropical faunal influence and provide further evidence that the southwest of the Arabian Peninsula can be considered as the northeastern limit of the Afrotropical Region (Bolton 1994, Robertson 2000).
Due to the position of the Arabian Peninsula in the interchange of three biogeographical regions, the Palearctic, Oriental, and Afrotropical, it is not surprising to observe shared faunal elements between these regions.The southwestern mountains of the Kingdom of Saudi Arabia and Yemen exhibit strong biogeographical affinities with the Afrotropical fauna (Eig 1938, Zohary 1973, Lehrer and Abou-Zied 2008, Doha 2009, Aldawood et al. 2011, Sharaf and Aldawood 2011, Sharaf and Aldawood 2012, Sharaf et al. 2012a, b, El-Hawagryi et al. 2013, Sharaf and Aldawood 2013, Sharaf et al. 2014).

Figure 1 .
Figure 1.Schematic line drawings of a Nesomyrmex species illustrating the measurements used (reproduced from Hita Garcia et al. 2017).A Body in profile with measuring lines for EL, WL, PH, PTH, and PPH B Mesosoma in dorsal view with measuring line for PW C Petiole and postpetiole in dorsal view with measuring lines for PTL, PTW, PPL, PPW D Head in full-face view with measuring lines for HL, HW, and SL E Dorsocaudal view of the propodeum with measuring line for PSL.
Francisco Hita Garcia personal collection, Okinawa Institute of Science and Technology, Onna-son, Okinawa, Japan KSMA King Saud University Museum of Arthropods, Plant Protection Department, College of Food and Agriculture Sciences, King Saud University, Riyadh, Kingdom of Saudi Arabia.