Redescription of the poorly known genus Ikuma Lawrence, with synonymy and description of a new species from Namibia (Araneae, Palpimanidae)

The spider genus Ikuma Lawrence, 1938, endemic to Namibia, is rediagnosed and redescribed based on the characters both species originally included in the genus and of the newly described I . larseni sp. nov. A new synonymy is proposed: I . squamata Lawrence, 1938, described from a sole female is recognized a junior synonym of the type species I . spiculosa (Lawrence, 1927), based on a single juvenile. The currently described I . larseni sp. nov. differs from the generotype in the eye arrangement, structure of the abdominal scuta, and details of the colouration. The copulatory organs of both males and females belonging to Ikuma are studied, described and depicted for the first time. The previously known genus range confined to the far north of Namibia extends to the mid-western part of this country.


Introduction
The small spider genus Ikuma was established by Lawrence (1938) to encompass two species: I. spiculosa (Lawrence, 1927) (transferred from Palpimanus Dufour, 1820) and I. squamata Lawrence, 1938. The genus was not diagnosed in detail, only briefly compared in the character of the body pubescence and of the eye arrangement with Palpimanus and Diaphorocellus Simon, 1893(sub Iheringia Keyserling, 1891. The type species, I. spiculosa, has originally been recognised as based on a juvenile. The only known specimen of I. squamata, when described, was claimed to be an adult female; however, no evidence of this statement has been provided. Many decades have passed since its description, and both the genus concept and the key generic characters of Ikuma have continued to be unclear. Platnick (1981) briefly reviewed the Palpimaninae and considered that this subfamily could be divided into two groups, each probably of the genus rank. Both these groups could be delimited by possessing an entire or divided abdominal scutum in the females. The species with an entire abdominal sclerite in the females he has undoubtedly assigned to Palpimanus. The question as to whether all of the remaining species also form a monophyletic group (for which, in his opinion, the name Ikuma would be available), Platnick intended to consider in a subsequent study which, however, has never been conducted and published.
The reason for Platnick (1981) considering the difference between Palpimanus and Ikuma as based chiefly on the aforenoted criterion remains uncertain. Lawrence (1938), when establishing Ikuma, did not textually describe the abdominal sclerites in Ikuma, and Platnick himself had not noted any of the two known species of Ikuma within the studied material. Nevertheless, this assumption was then mentioned by Dippenaar-Schoeman and Jocqué (1997), who cited the mentioned review, refraining from their own comments. Until now, Ikuma has been thus treated as a once described and then completely forgotten taxon with dubious characters.
The present attempt to find criteria for reliably distinguishing between the genera of Palpimaninae was triggered by two interdependent events. First, among the studied palpimanids from Namibia, we have revealed a few palpimanine spiders that looked completely different to Palpimanus spp. On the other hand, by our request we have received a fortunate opportunity to look, albeit remotely, at the holotype of Ikuma spiculosa. As a result, we identified the noted specimens as certainly belonging to Ikuma and representing a yet-undescribed species. The type series of this new congener is diagnosed, described and illustrated herein. Photographs were taken using an Olympus SZX16 stereomicroscope with a Canon EOS 7D (Turku) or Canon EOS 80D (Tel Aviv) camera and prepared using the Helicon Focus 7.6.2 Pro software (http://www.heliconsoft.com). Measurements were taken through the above-mentioned stereomicroscope to an accuracy of 0.01 mm. All measurements are given in millimetres. The maximum length of the clypeus along the midline was measured from the anterior edge to the perpendicular line connecting the anterior edge of both AME; the smaller lateral clypeus length, measured from the anterior edge of ALE and the closest point of the anterior clypeus edge, follows the maximum clypeus length, being enclosed in brackets. The length of the sternum was measured along a straight line between the posterior tip of the sternum and the hindmost part of the labium. Lengths of leg and palp segments were measured on the dorsal side, with lengths of every measured segment from the midpoint of the anterior margin to the midpoint of the posterior margin.

DNMNH
Illustrations of the dissected vulva, placed into a small Petri dish filled with a 85% lactic acid, were made after cleaning the object in 10% potassium hydroxide aqueous solution for several hours and exposing it for a few minutes in an alcohol solution of Chlorazol Black.

AER
anterior eye row; ALE anterior lateral eye; AME anterior median eye; CL carapace length; CW carapace width; CyL clypeus length; MOQ median ocular quadrangle; PER posterior eye row; PLE posterior lateral eye; PME median lateral eye; TL total body length in dorsal view.
Other abbreviations used are encoded in the text and in the captions.

Taxonomy
Family Palpimanidae Thorell, 1870 Note. Since Platnick (1975), the family is considered consisting of three subfamilies: the mostly Paleotropical Chediminae Simon, 1893, the purely Neotropical Otiothopinae Platnick, 1975, and the nominative subfamily Palpimaninae. The distributional peculiarities of the latter subfamily are considered below.

Subfamily Palpimaninae
Notes. This subfamily differs from the Otiothopinae by possessing accessory terminal sclerites in the male bulb (which are absent in the males belonging to the latter subfamily; see Platnick 1975). The Palpimaninae can be distinguished from the Chediminae in having eight eyes with widely spaced ALE and PLE vs. two, six or eight eyes with contiguous or lacking ALE and PLE in the chedimine spiders (Zonstein and Marusik 2017). The subfamily is distributed in the Old World, where its range is limited to the Mediterranean, Sahara-Sind region (including Middle East, Gujarat and Central Asia), and the mainland Sub-Saharan Africa. The record of Palpimanus argentinus Mello-Leitão, 1927 in South America, based only on the types, has not been confirmed by later field studies, and may refer either to a sole introduced species (Platnick 1975) or, even more likely, to the incorrectly interpreted collection data (Zonstein and Marusik 2017). The Palpimaninae are divided between two sharply uneven groups of the genus rank: a species-rich Palpimanus Dufour, 1820, with 38 named species distributed throughout the entire subfamily range (WSC 2022), and a small Namibian genus Ikuma Lawrence, 1938, embracing only two species.

Genus Ikuma Lawrence, 1938
Ikuma Lawrence, 1938: 217. Type species. Palpimanus spiculosus Lawrence, 1927, by original designation. Emended diagnosis. Ikuma (I.) well differs from Palpimanus (P.) in the shape of the carapace (anteriorly narrowed, ovoidal and gently elevated from the edges to the domed central part in I. vs. round-oval and steeply edged in P.), in the clypeus (inclined in I., vertical in P.), and in the shape of the sternum (longer and visually narrower, ending posteriorly behind coxae IV in I. vs. shorter, looking subrounded, and ending posteriorly at the axes of coxae IV in P.). The whitish adpressed pubescence on the dorsal and lateral surface of the carapace is much longer and denser in I. (where it is present also on the dorsal abdomen) than in P. (where a similar pubescence is much shorter and sparser, and confined only to the carapace). The embolus is small, fragile and membranous in I. vs. relatively large, branched and with partially sclerotized structures in P. The adult females of these genera can be distinguished by the structure of the endogyne, either possessing (P.) or lacking (I.) heavily sclerotized parts.
Palps short, legs I-IV moderately long. Leg formula: 4132. Leg I robust, with considerably swollen and laterally flattened femur, with patella longer that tibia, and tarsus longer than metatarsus (Figs 1B, 2B, D). Tibia and metatarsus I with wide and dense prolateral scopula. Leg tarsi II-IV relatively short; two tarsal claws narrow and provided with several short teeth. Claw tufts well-developed (as in Fig. 7A).
Abdomen fusiform, in unsclerotised part with contrasting dorsal pattern or uniformly pale coloured. Abdominal scuta conforming a rather short pedicel tube; dorsal portion of scutum narrow, small and narrowly separated from both pedicel tube and large scoop-like ventral portion. Small spinneret group set on low mound (see Fig. 7B). AMS small, cylindrical, two-segmented; PMS and PLS reduced to a few sessile spigots in females and absent in males.
Diagnosis. There are a number of significant differences between Ikuma spiculosa and I. larseni sp. nov. It concerns the coloration of the abdomen (contrastingly bicolorous vs. uniformly pale), position of the appressed pubescence on the carapace (mostly subcentral vs. sublateral), and the relative length of interdistance AME-AME (longer than AME-ALE vs. shorter than AME-ALE).
Description (based on seemingly non-adult specimens). The species was in fairly sufficient details described by Lawrence (1927Lawrence ( , 1938. See also Fig 1. Distribution. Oshikoto Region in northern Namibia. Notes. The aerial distance between the type localities of Ikuma spiculosa and I. squamata, Namutoni and Ikuma River, is less than 100 km. Both are situated at the same elevation, and they adjoin the same saline depression Etosha Pan. The holotype specimens of the two species do not differ in the peculiarities and details of their pubescence and overall colouration. Judging from the original descriptions, these types can be distinguished only by their size (TL 3.6 in I. spiculosa vs. 5.5 in I. squamata). Applied to the difference in the body size between these specimens and the type series of I. larseni sp. nov. (TL 10.7-12.1), it may simply indicate that these non-adult specimens can be, respectively, a younger and an elder instars belonging to the same species. Hence, Palpimanus spiculosus Lawrence, 1927 is considered here a senior synonym of Ikuma squamata Lawrence, 1938, syn. nov Etymology. The specific name is a patronym after Norman Larsen (Cape Town, South Africa) who kindly provided us with the macro-photographs of the preceding Ikuma species.
Diagnosis. Ikuma larseni sp. nov. can be distinguished from I. spiculosa by the colouration and pubescence (carapace with densest pubescence along margins vs. in subcentral part of the carapace); the new species has a uniformly pale abdomen vs. bicolorous in I. spiculosa ( Fig. 2A, C cf. Fig. 1). The interdistance AME-AME is longer than AME-ALE in I. larseni sp. nov. and shorter in I. spiculosa. Since characters of I. spiculosa seem to be based on the juvenile or subadult specimens, the comparison of the copulatory organs remains impossible.
Variation. In paratype females, the length of the carapace varies from 4.4 to 5.6 mm.
Habitat. According to the collecting data, the specimens were obtained by sand sifting.
Distribution. Known only from the type locality. Note. Since the only available male of Ikuma larseni sp. nov. was found partially damaged (probably when collected), we preferred to designate one of the better preserved females as the holotype.