Revision of the ant-eating spider genus Mallinus Simon, 1893 (Araneae, Zodariidae)

Abstract The zodariine spider genus Mallinus Simon, 1893 is redescribed and diagnosed. The type species, M.nitidiventris Simon, 1893 from South Africa, was originally described from subadult specimens. Adults of both sexes of M.nitidiventris are described for the first time, based on recently collected material, and the genus is rediagnosed, redescribed, and its relationships discussed. A single aberrant male specimen from Namibia is here described as a morphospecies, as it is presumed to only be superficially related. A second species, M.defectus Strand, 1906 from Tunisia, is considered a ‘species inquirenda’, as the type specimens could not be traced, but this species is in any case unlikely to be congeneric. The genus is one of 10 cases of a monotypic genus in the Zodariidae. Notes are provided on the biology of M.nitidiventris.


Introduction
The Zodariidae is a medium-sized family of spiders, with 1140 species in 85 genera globally (World Spider Catalog 2018). The subfamily Zodariinae is of particular interest from a biological perspective, as most of the species are exclusively myrmecopha-gous (Cushing 2012, Pekár et al. 2012, Pekár and Toft 2015, Komatsu 2016, which reflects its derived phylogenetic position in the family (Jocqué 1991).
The genus Mallinus Simon, 1893 remains one of the most poorly understood genera of Zodariinae. Initially described from a single South African locality, the type species (M. nitidiventris Simon, 1893) has never been properly redescribed, as the type series consists of a subadult male and subadult female (Jocqué 1991), not adult specimens as indicated by Simon (1893). A second species, M. defectus Strand, 1906, was described from Tunisia (Strand 1906) in the Palaearctic Region, but it was doubtfully placed in Mallinus originally, and as explained in the discussion it is unlikely to belong to this genus. Simon (1893) placed Mallinus in his "Zodarieae" together with Zodarion Walckenaer, 1826 and Diores Simon, 1893, although the concept of this subfamily has expanded significantly since then through a series of revisions led by the third author (Jocqué 1991;World Spider Catalog 2018).
The recent collection of adult specimens in South Africa fitting Jocqué's (1991) illustrations of M. nitidiventris served as the impetus to redescribe the type species and assess whether other congeneric species may occur in Africa. Examination of museum collections yielded several additional records of M. nitidiventris, indicating a surprisingly broad distribution of the species in the arid Nama Karoo Biome of South Africa, but also extending into the Succulent Karoo and the arid parts of the Savanna Biome. A revised diagnosis and description, aided by scanning electron micrographs, are provided to recognize Mallinus from other Zodariinae spiders.
A single male from northern Namibia is here described as "Mallinus" sp. Although the shape and the texture of the cephalothorax and the abdomen are similar to that of M. nitidiventris, we suppose that it belongs to a different genus, mainly due to the absence of a conductor on the male palp and the extremely unusual eye pattern: the AME are much larger than the remainder and the ALE are very wide apart, situated in the far lateral corners of the clypeus. However, we have refrained from describing a new genus on the base of a single male, and await further material to place it.

Materials and methods
The specimens examined in the current study were preserved in 70% ethanol and examined using a Nikon SMZ800 stereomicroscope for measurements and descriptions. The female genitalia and male palps were drawn with a WILD M10 stereomicroscope (Leica). The female genitalia were then dissected and digested using half a tablet of Total Care Enzima product (protein removal system originally for cleaning contact lenses and containing subtilisin A-0.4 mg per tablet; Abbott Medical Optics, Santa Ana, CA) in a few millilitres of distilled water overnight, and then immersed in 75% ethanol. These female genitalia and male palps were photographed with a Leica MZ16 using the Leica Application Suite (LAS) automontage software (ver. 3.8; Leica, https://leicacamera.com).
All measurements are given in millimetres (mm). Measurements of somatic morphological structures were taken from one specimen of each sex, as indicated, while total length measurements were taken for all available specimens to determine size vari-ation. Leg lengths are presented as the sequence from femur to tarsus, and total. Digital photographs of the dorsal and lateral habitus of both sexes of M. nitidiventris were taken with a Nikon D5-L3 camera system attached to a Nikon SMZ800 stereomicroscope. To increase depth of field, a series of images was taken and stacked using the Combin-eZM imaging software (http://www.hadleyweb.pwp.blueyonder.co.uk).
Material for scanning electron microscopy (SEM) was freshly collected from the farm Bankfontein in the western Free State, South Africa (see Material examined) and immediately preserved in 100% ethanol (see below). Prior to SEM, material was transferred to fresh 100% ethanol overnight, critical point dried in an argon chamber, glued to aluminium stubs using double-sided tape, and sputter coated with gold. Somatic and genitalic structures were examined in a JEOL JSM-7800F FE-SEM at 3 kV and digital photographs were taken.
The following abbreviations are used in the descriptions: AER -anterior eye row; AH -abdomen height; AL -abdomen length; ALE -anterior lateral eye; ALS -anterior lateral spinneret; AME -anterior median eye; AW -abdomen width; CL -carapace length; CW -carapace width; F -femur; FL -fovea length; imm. Diagnosis. Mallinus can be distinguished from other zodariine spiders by the relatively smaller size of the anterior median eyes, which are only slightly larger than the lateral and posterior eyes, while generally much larger than the other eyes in other zodariines. Mallinus shares with Palfuria Simon, 1910 the scale-like extensions on the endites and the considerably raised cephalic region, but lacks the carapace modifications at the posterior end of the cephalic region typical for most Palfuria (Szüts and Jocqué 2001); rather, the carapace slopes steeply at the posterior end of the cephalic region, with only a shallow transverse depression. Mallinus also have a very globose abdomen, which is usually higher than long in both sexes, a rare condition amongst other zodariines.
Relationships. In a morphological phylogeny of Zodariidae, Jocqué (1991) placed Mallinus in the Zodariinae, as sister group to Ranops Jocqué, 1991 + Zodarion. However,   its position would have been clearer had adult specimens been available for study. This lack resulted in a considerable number of missing entries in the character matrix relating to genitalic morphology. Henrard and Jocqué (unpubl.) include a single male M. nitidiventris (from Tswalu Kalahari Reserve, MRAC 216253) in their molecular phylogeny of Zodariidae. Their results suggest that Mallinus is most closely related to Palfuria. This sister group relationship is also well supported by morphological characters. Mallinus shares with Palfuria the deeply granulate tegument of the carapace, the strongly raised cephalic region with a steep slope in the posterior half, the scale-like extensions on the endites, the circumferential folds of the abdomen (this character is conspicuous in males and females when the abdomen is not distended), and the subdistal suture on the tarsi. The subdistal suture was also observed in Akyttara Jocqué, 1987 andHeradida Simon, 1893, to which they are also closely related. In the phylogeny of Henrard and Jocqué (unpubl.), Ranops appears to be placed as the sister group of a clade containing Akyttara, Heradida, Mallinus and Palfuria, forming a strongly supported monophyletic group. Those zodariines belong to a monophyletic clade characterized by the presence of a unique femoral organ on the legs (Henrard and Jocqué 2017).   Colour: carapace orange-brown, with faint black mottling and striae (Figs 1, 2); chelicerae orange; endites yellow, slightly darker retrolaterally at midpoint; labium orange, cream distally; sternum orange, cream along anterior margin; leg femora orangebrown; patellae yellow proximally, orange brown distally; tibiae and metatarsi light brown proximally, yellow-brown distally; tarsi yellow; palps yellow-brown; abdomen black dorsally, grey ventrally along midline, with large white patches laterally, fused narrowly in ring around anterior of abdomen; spinnerets creamy-yellow. Eyes: AME diameter 1.1 times ALE diameter; AME separated by distance equal to 0.76 times their diameter; AME separated from ALE by 0.4 times AME diameter; clypeus height 4.2 times AME diameter at AME, 4.16 times ALE diameter at ALE; PME and PLE equal in diameter; PME separated by distance equal to 1.15 times their diameter; PME separated from PLE by distance slightly less than 1.21 times PME diameter; CW:PERW = 2.06:1. Legs spineless, covered in short erect setae and incised setae. Abdomen slightly longer than carapace, higher than long or broad, with shiny scutum covering most of dorsum (Figs 1, 2); dorsum sparsely covered in short straight setae, denser on posterior slope and venter. Epigyne as in genus description (Figs 43,47,50,51). Other characters as in genus description.
Morphology and colouration similar to female (Figs 3, 4), except for the following: AME diameter equals 1.16 times ALE diameter; AME separated by distance 0.67 times their diameter; AME separated from ALE by distance 0.38 times AME diameter; clypeus height 3.85 times AME diameter at AME, 4.0 times ALE diameter at ALE; PME diameter equals 0.89 times PLE diameter; PME separated by distance 1.25 times their diameter; PME separated from PLE by distance 1.25 times PME diameter; CW:PERW = 2.17:1. Abdomen relatively smaller than female (Figs 3, 4), shorter than carapace, as high as long, slightly longer than broad, with conspicuous circumferential folds. Palp as in genus description (Figs 44,48,49,52,53).
Variation. Populations from the south-western parts of the species' range (including the type locality) have a clearly darker carapace and legs, which are wine-red in colour (Figs 54-57). It is plausible that populations in this part of its range may associate with a darker species of model ant, affecting their colouration.
Distribution. Widespread in the western half of South Africa, known from the Eastern Cape, Western Cape, Northern Cape and Free State Provinces (Fig. 67).
Habitat and biology. Mallinus nitidiventris is widespread in the semi-arid and arid western half of South Africa, with records in the Nama Karoo and Succulent Karoo biomes, extending into the arid savannas of the southern Kalahari Desert. Specimens collected at Bankfontein in the western Free State Province were all found in Nama Karoo scrubland, either along a hillside or open plains. The substrate at both sites comprised fine Ecca Shale alluvium, siltstone and sandstone gravels that form part of the Ecca Group of the Karoo Supergroup (A. Odendaal and J. Fourie, pers. comm.). Some of the Bankfontein specimens (NCA 2015/1818) were collected during mid-morning (10:00-12:00) foraging in open ground in the vicinity of various ants, including Anoplolepis custodiens F. Smith, 1858, Camponotus spp., Messor sp. and Monomorium sp. Of these, Mallinus nitidiventris most closely resembled Messor sp. in terms of colouration, although workers of this ant were almost double the body length of the spiders. Only one of these five spiders sampled at this specific site was feeding, a female consuming a Monomorium worker ant that measured approximately 2 mm in length, suggesting that this species is myrmecophagous, as are most Zodariinae. Remarks. We have included the description of a second species in this paper based on a single poorly preserved male from Namibia without formally naming it, as it shows several clear differences to M. nitidiventris that make its generic placement dubious: 1) the lack of a palpal conductor on the palp, and 2) the AME that are much larger than the others, and the ALE that are very wide apart and situated in the far lateral corners of the clypeus. This species most likely represents a new genus, and we hope that its description and illustration here will encourage researchers to find fresh material of both sexes and describe and diagnose this taxon thoroughly.
Male ( Colour: carapace medium brown (Figs 58, 60), with dark area around AME, darker stripe between PME (Fig. 61) and dark radiating striae; chelicerae medium brown; endites and labium pale brown; sternum pale brown, with thin darker margin (Fig. 59); leg femora, patellae and tibiae uniform pale brown; metatarsi and tarsi yellow; abdomen dark sepia dorsally (Fig. 58), pale grey laterally and ventrally, area in front of epigastric furrow yellow; spinnerets creamy-yellow. Carapace: cephalic region very broad, almost as broad as thoracic region (Fig. 58); texture finely granulate, without setae. Eyes: AME largest, diameter 1.9 times ALE diameter; AME separated by distance equal to 0.3 times their diameter; AME separated from ALE by 1.6 times AME diameter; clypeus height 1.9 times AME diameter at AME, 2.9 times ALE diameter at ALE; ALE very far apart, situated in far lateral corners of clypeus (Fig. 61); PME and PLE subequal in diameter; PME separated by distance equal to 3.0 times their diameter; PME separated from PLE by distance slightly less than 2.2 times PME diameter; CW:PERW = 2.06:1. Sternum shield-shaped (Fig. 59), shallowly rebordered along lateral margins, with few scattered short setae. Legs with few spines (spination of specimen probably incomplete: FII v1 III v1; TI v1-1 II v1), with some dispersed short erect setae and incised setae. Abdomen slightly shorter than carapace, almost as high as long or broad, with shiny scutum covering most of dorsum and clear circumferential folds (Fig. 62); dorsum sparsely covered in short straight setae, denser on posterior slope and venter; venter sclerotized in front of epigastric fold, with wide, transverse inframamillary sclerite. Palp with long, straight, strongly tapered, sharp RTA; embolus simple, slightly curved; MA membranous, looping; conductor absent (Figs 63, 64). Other characters as in genus description of Mallinus.
Female unknown. Distribution. Only known from a single locality in north-western Namibia (Fig. 67).

Discussion
Most of the 85 genera in the Zodariidae are known from more than one species or are speciose (e.g. Mallinella Strand, 1916 with > 200 species), although 10 genera can be considered monotypic following this revision (World Spider Catalog 2018). Mallinus, Figure 67. Distribution of Mallinus nitidiventris (type locality, red circle; other localities, yellow circles) and "Mallinus" sp. (red square) in southern Africa. ? indicates immature specimen requiring confirmation.
which is now well defined, appears to be one of the uncommon cases of monotypy. Mallinus nitidiventris appears to have a large distribution (Fig. 67), which is also a rare phenomenon in the subfamily Zodariinae. Although it is presently known only from the more arid western half of South Africa, it may possibly also occur in nearby southern Botswana and Namibia. At least for the latter, we could not confirm its occurrence in the country, as the collection of the State Museum in Windhoek, Namibia has no invertebrate curator to currently process specimen loans. The second species, Mallinus defectus Strand, 1906 from Tunisia, was only tentatively attributed to the genus, as Strand (1906) put a question mark behind the genus name: Mallinus (?) defectus. Considering the predominant distribution patterns of the genera in the Zodariidae, it is most unlikely that the genus occurs both in South and North Africa. It would be the only example of such a distribution. The description of the species by Strand (1906) does not provide a single clue as to the real identity of the genus to which the species belongs. Unfortunately, the type specimens could not be traced, and the species should therefore be considered a 'species inquirenda'.
The distribution of this monotypic genus thus remains exceptionally large, and it is not clear why it has remained like this.