Illustrations and measurements were made with the aid of a Wild M5 stereo-microscope with a drawing tube (camera lucida) and an ocular micrometer. Measurements follow Stahnke [15] and are given in mm. Trichobothrial notations follow Vachon [16] and morphological terminology mostly follows Vachon [17] and Hjelle [18].

The region of Ghardaïa is located in the North of the Central Algerian Saharan region (Fig. 1) and covers a total area of ca. 86,560 km². The average altitude of the main reliefs is of 520 meters. Geomorphological features are constituted by the Wadis and the Regs [19]. The region is characterized by a dry Saharan climate with extreme thermal amplitudes between the day and the night, reaching 15–16 degrees [20]. The coldest month is January with a minimal temperature of 6.2 °C, whereas the hottest month is July with a maximum temperature of 41.8 °C.

Rainfall is extremely low in the region of Ghardaïa with an average value of 80.2 mm per year. Air humidity is rather weak with a maximum value of 55.5% in December and a minimum of 21.6% in July [21]. Analysis of dry periods over several years attest that 11 months are dry, ranging from February to December; only a short and slightly more humid period can be experienced in January.

The new species described here was collected in a zone of desert rocks and grasses–Regs and Wadis (Figs. 2–3). This species seems to present some fossorial activities, since it digs small and shallow, from 3 to 15 cm deep, shelters (Fig. 4). Buthus saharicus sp. n. does not show the characteristics of a psammophilic element. Even if this area of the Sahara desert, in Central Algeria, is quite arid, it does not really have the characteristics of sand dunes deserts (Ergs).

As outlined in previous North African scorpion studies [7] the present pattern of distribution of the flora and fauna currently encountered in the Sahara may well be very old and most certainly reflects not only the consequences of palaeogeographic factors, but is also largely the result of various palaeoclimatic vicissitudes [22]. These palaeoclimatic events had an important impact during the Quaternary when extended areas at higher latitudes in Europe (and elsewhere) were covered with ice. During these, Africa experienced periods of intense rain and, additionally, an increase in the amount of ice on the mountains (particularly in Oriental Africa). The last documented wet period in the Sahara ended as early as 3000 years BP.

The present composition of the Saharan scorpion fauna is actually a heritage of ancient faunas present in North Africa since the beginning of or, at most, middle Cenozoic times [17]. North Africa has experienced numerous paleoclimatological vicissitudes in the last few million years, the latest occurring in the past thousands of years in the recent quaternary periods. The Sahara has undergone a series of wet periods, the most recent occurring 10,000–5000 years BP, and it was not until about 3000 years BP that the Sahara assumed its present arid state [23–25]. Even though recent studies suggest that the Sahara desert may be much older than was previously thought [26], it seems reasonable to postulate that extremely arid areas have always existed as patchy desert enclaves, even when the general climate of North Africa enjoyed more mesic conditions. In these desert regions, a specialized scorpion fauna would have evolved. In contrast, other lineages less well adapted to drought, and previously present only in more mesic environments, probably experienced important regressions in their distribution. In other cases, populations have been reduced to restricted and patchy zones sometimes with remarkable disjunctions in their distribution patterns. Given the paucity of distribution data for some Buthus populations with modern distributions limited to more mesic environments (Fig. 5), it is difficult to decipher a precise model. However, there is evidence that some of these lineages have been present in North Africa for at least 10 to 15 My [8,27].

The patterns observed today in the distribution of North African scorpions can be summarized as following: (i) a core Saharan region defined by Vachon [17] as the ‘central compartment’ in which only the groups best adapted to xeric conditions have a large distribution; and (ii) a peri-Saharan zone of distribution almost forming a ring around the most arid core region of the Sahara. In this zone many groups better adapted to more mesic conditions are encountered, including several Buthus populations [1].

As suggested by Vachon [17], several groups less well adapted to xeric environments have their populations limited to refugia. These can be represented by some oases and in particular by the Saharan massifs. In contrast, the presence of species belonging to groups associated with ‘ancient lineages’ in mesic environments, as it seems to be the case for the species belonging to the genus Buthus, may suggest a secondary re-adaptation. This could explain the presence of endemic species of Buthus in several Saharan massifs and Mountain ranges [3,7].

Family Buthidae C. L. Koch, 1837

Genus Buthus Leach, 1815

Buthus saharicus sp. n. (Figs. 6–8)

Algeria, region of Ghardaïa (32°18’N, 003° 50’E), in Wadi bed, buried in shelter, 436 m, 14/II/2015 (S.E. Sadine), female holotype; 4/VI/2015 (S.E. Sadine), 1 male paratype; 14/II/2015 (S.E. Sadine & A. Houtia) 1 female juvenile paratype. Holotype and female juvenile paratype deposited in the “Muséum national d’histoire naturelle”, Paris; male paratype deposited in the University of Ghardaïa, Algeria.

Etymology: The specific name refers to the Sahara desert where the type material has been collected.

Diagnosis: Scorpion of moderate size, reaching a total length of 67 and 52 mm in female and male respectively. General coloration yellow to pale yellow without spots; only some carinae are slightly reddish in adults; juveniles with some dark spots over carinae and on metasomal segment V. Carinae moderately to strongly marked; ventral carinae of metasomal segments II–III strongly lobated; two lateral lobes on metasomal segment V with one smaller lobe in between these two lobes; granulations moderately to weakly marked. Fixed and movable fingers with 11-11 rows of granules. Pectines with 27 to 29 teeth in females, 31 teeth in male. Trichobothrial pattern A-β (beta), orthobothriotaxic; trichobotrium d₂ of femur extremely reduced, and db on fixed finger displaced to the internal face. Tibial spurs strongly developed.

Relationships: B. saharicus sp. n. certainly belongs to the ‘B. occitanus’ complex of species. The new species is, however, quite singular by its very pale pattern of pigmentation. It can be distinguished from other species of Buthus and in particular from B. tunetanus and B. paris, species distributed in the North range of Algeria, by the following characters: (i) the new species has a paler color pattern, without any spots in adults, (ii) the new species has a reduced number of pectinal teeth compared to B. tunetanus, (iii) B. paris has 12-14 rows of granules on the chela fingers whereas the new species has 11-11, (iv) B. saharicus sp. n. shows a weak setation on pedipalps, metasomal segments and telson (‘oligotriche’, sensu Vachon [17]); this setation is better marked in the other two species, (v) ventral carinae on segments II–III have strongly lobate granules in the new species, (vi) in the new species, lateral lobes on metasomal segment V have one smaller lobe in between the two lobes, and (vii) in the new species metasomal segment I is longer than wide whereas in both B. tunetanus and B. paris it is wider than long [28].

Description based on female holotype and paratypes. Measurements after the description.

Coloration basically yellow to pale yellow without spots; only some carinae are slightly reddish in adults; juveniles with some dark spots over carinae and on metasomal segment V. Prosoma: carapace yellow with reddish carinae; eyes marked by dark pigment. Mesosoma yellow without spots; the median carina reddish. Metasomal segments yellow with some reddish spots over carinae; vesicle pale yellow; aculeus reddish-yellow at its base and dark red at its extremity. Venter yellow; pectines and genital operculum pale yellow. Chelicerae pale yellow with some vestigial variegated spots at the base of fingers; fingers yellow with reddish teeth. Pedipalps yellow with carinae and oblique rows of granules in fingers slightly red. Legs pale yellow.

Morphology. Carapace moderately to weakly granular; anterior margin with a weak concavity. Carinae moderately to strongly marked; anterior median strongly granular, central median and posterior median carinae moderately granular, with ‘lyre’ configuration. All furrows moderate. Median ocular tubercle slightly anterior to the center of carapace. Eyes separated by more than two ocular diameters. Four pairs of lateral eyes; the first three of moderate size in relation to median eyes; the fourth pair reduced in size. Sternum triangular, not narrowed; slightly wider than long. Mesosoma: tergites moderately granular. Three longitudinal carinae moderately to weakly crenulate in all tergites; lateral carinae strongly reduced in tergites I and II. Tergite VII pentacarinate. Venter: genital operculum divided longitudinally, which plate with a semi-oval to semi-triangular shape. Pectines: pectinal tooth count 29-28 in female holotype (paratypes with 27-27-female and 31-31-male); middle basal lamella of the pectines not dilated. Sternites without granules, smooth with elongated spiracles; four carinae on sternite VII; other sternites acarinated and with two vestigial furrows. Metasomal segments with a weak setation; segments I to III with ten crenulated carinae; ventral strongly marked on II–III, with conspicuous lobate granules; segment IV with eight carinae, crenulated; all segments with a smooth dorsal depression; segment V with five carinae; the latero-ventral carinae crenulate with 5–6 lobate denticles posteriorly; ventral median carina divided posteriorly over 1/2 of the segment length; anal arc composed of 6–7 ventral teeth, and two strong lateral lobes with a third smaller lobe in between the other two. Intercarinal spaces weakly granular. Telson with a few minute granulations ventrally, almost smooth; aculeus curved and shorter than the vesicle, without a subaculear tubercle. Cheliceral dentition as defined by Vachon [29] for the family Buthidae; external distal and internal distal teeth approximately the same length; basal teeth on movable finger small but not fused; ventral aspect of both fingers and manus covered with long dense setae. Pedipalps with a moderate setation; femur pentacarinate; patella with eight carinae, strongly marked; all faces weakly granular to smooth; chela smooth, with vestigial carinae. Fixed and movable fingers with 11-11 oblique rows of granules. Internal and external accessory granules present, moderately strong; three accessory granules on the distal end of the movable finger next to the terminal denticle. Legs: tarsus with two longitudinal rows of long setae ventrally; tibial spurs very strong on legs III and IV; pedal spurs strong on legs I to IV. Trichobothriotaxy: trichobothrial pattern of type A, orthobothriotaxic as defined by Vachon [16]. Dorsal trichobothria of femur arranged in β (beta) configuration [30]; trichobotrium d₂ of femur extremely reduced, and db on fixed finger displaced to the internal face.

Morphometric values of the female holotype of B. saharicus sp. n. Total length including the telson 67.3. Carapace: length 7.6, anterior width 5.7, posterior width 9.0. Metasomal segments: I length, 5.2, width 4.9; II length 5.8, width 4.6; III length 6.0, width 4.5; IV length 6.7, width 4.3; V length 8.5, width 4.1, depth 3.2. Telson length 7.2, vesicle: width 4.0, depth 3.5. Pedipalp: femur length 6.6, width 2.1; patella length 7.3, width 2.8; chela length 12.6, width 3.3, depth 3.5; movable finger length 8.0.

The authors declare that they have no competing interest.