Microbuthus Kraepelin, 1898

Lowe, Graeme, Kovařík, František, Stockmann, Mark & Šťáhlavský, František, 2018, Review of Microbuthus with description of M satyrus sp n (Scorpiones Buthidae) from Oman and Yemen, Euscorpius 263, pp. 1-22 : 2-4

Microbuthus Kraepelin, 1898

( Figs. 1–86, Table 1)

Microbuthus Kraepelin, 1898: 42 .

Microbuthus: Fet & Lowe, 2000: 181–182 ; Lowe, 2010: 2–17 , figs. 1–41 (complete synonymy and reference list up to 2010); Lourenço, 2011b: 327–331, figs. 1– 8; Loria & Prendini, 2014: 19, 25; Kovařík et al., 2016: 20, 115; Loria & Prendini, 2018: 184, tab. 1.

TYPE SPECIES. Microbuthus pusillus Kraepelin, 1898 (= M. litoralis (Pavesi, 1885))

DIAGNOSIS. Small to very small buthid scorpions (Kovařík, 2009; Sissom, 1990), adults <25 mm long; body dorsoventrally compressed; carapace strongly trapezoidal, surface densely granular, carinae indistinct, preocular area sloped downward with narrow anterior marginal shelf; 4 pairs of lateral eyes; tergites granular, weakly monocarinate or tricarinate; carapace, tergites, metasoma and pedipalps bearing short, clavate microsetae; sternite posterior margins finely microdenticulate or smooth; metasoma with segments I–III granulate, reticulate or rugose, with distinct carinae, segments IV– V expanded, heavily sclerotized, with lateral and ventral surfaces smooth, convex, bearing numerous pits or depressions; ventrolateral carinae of V obsolete, or smooth to crenulate; telson vesicle abbreviated, deep, steeply sloped or truncated posteriorly, narrower than metasoma V, with ventromedian carina bearing series of regular transverse granules, lacking subaculear tubercle; aculeus short, stout, sharply bent; pectines with <16 teeth, fulcra and middle lamellae present; hemispermatophore with flagellum separated from tripartite sperm hemiduct, capsule with hook-like basal lobe; chelicera with characteristic buthid pattern of dentition ( Vachon, 1963), fixed finger armed ventrally with two large denticles nearly equal in size; pedipalp chela slender, with long, narrow, curved fingers leaving wide gap when closed; fixed finger moderately to strongly deflected upward at base, strongly curved, base with interior and exterior lobes overhanging articulation of movable finger; dentition reduced, not clearly divided into subrows of primary denticles, with non-imbricated linear series of non-contiguous, minute granules separated by several enlarged spiniform denticles; both fingers with enlarged apical teeth; neobothriotaxic minorante, type Aβ ( Vachon, 1974; 1975): femur: 2 external, 3 dorsal (d 2 and d 5 absent), 4 internal; patella: 6–7 external (em may be absent), 4 dorsal (d 2 absent), 1 internal, d 3 straddling dorsomedian carina; manus: 4 external (Eb 3 and Esb absent), 2 ventral; fixed finger: 6 (esb absent), eb at base of finger, est and et in basal half of finger, db and dt in apical half of finger with db displaced distal to dt, it distal to db; legs III–IV with tibial spurs present, reduced or lost; retrosuperior margins of basitarsi I–III with or without bristle-combs.

SUBORDINATE TAXA. M. fagei Vachon, 1949 ( Mauritania) ; M. flavorufus Lourenço et Duhem, 2007 ( Egypt) ; M. gardneri Lowe, 2010 ( Oman) ; M. kristensenorum Lowe, 2010 ( Oman, Yemen?); M. litoralis (Pavesi, 1885) ( Djibouti, Eritrea, Yemen); M. maroccanus Lourenço, 2002 ( Morocco, Western Sahara, new record); M. satyrus sp. n. ( Oman, Yemen).

HEMISPERMATOPHORES. The hemispermatophores of three species of Microbuthus examined here ( M. gardneri , M. kristensenorum and M. satyrus sp. n.) were morphologically similar, with elongated trunk, short capsule region and a relatively short tapered flagellum with pars recta and pars reflecta. The flagellum is well separated from a tripartite sperm hemiduct composed of posterior and median lobes joined along a suture or carina, and a separate anterior lobe. An isolated hooklike basal lobe arises proximally at the base of the median lobe. Similar capsule structures have been described for M. fagei by Vachon (1949: 391, fig. 466; 1952: 319, fig. 466) and previously for M. gardneri by Lowe (2010: 6, figs. 15–16).

In their cladistic analysis of buthids based on trichobothriotaxy, Fet et al. (2005) tentatively placed the genus Microbuthus in the Buthus group, although there was uncertainty because patellar trichobothrium d 3 straddled or bisected the dorsomedian carina (DMc); d 3 internal to DMc is diagnostic for the Buthus group. Lowe (2010: 47) discussed this ambiguity but left the question unresolved. Since then, we have studied hemispermatophores of many buthids and proposed that a capsule with tripartite sperm hemiduct and basal lobe (‘3+1’ configuration) separated from the flagellum is diagnostic for the Buthus group ( Kovařík et al., 2016). This could be an independent character supporting membership of Microbuthus in that group.

Recently, we conjectured that the form of the basal lobe could have taxonomic value at the species level in some buthids (e.g. the genus Gint ; Kovařík et al., 2018). Here, we find that the basal lobe of M. satyrus sp. n. ( Figs. 50–52) differs in size and shape from that of M. gardneri , i.e. it is shorter, more robust, curved and hornshaped, compared to the longer, narrower, linear, fingershaped lobe of M. gardneri ( Figs. 55–57). A long, narrow basal lobe was also observed previously in a different specimen of M. gardneri ( Lowe, 2010: 6, figs. 15–16), suggesting that there is a consistent difference. This is a potential diagnostic character that warrants further study of intraspecific variation. We also note that basal lobes of two specimens of M. kristensenorum examined here were similar to each other ( Figs. 51–53, 55–57), and differed from that of M. gardneri .

KARYOTYPES. In this study, we analyzed chromosomes of the male holotype of M. satyrus sp. n. ( Fig. 83), one male of M. gardneri ( Fig. 84) and two males of M. kristensenorum from two different localities, Arlit and W of Qairoon Hairitti ( Fig. 85). In all investigated males the chromosomes were holocentric and the meiosis was achiasmatic. Both characters are typical for the scorpions from the family Buthidae (e.g. Mattos et al., 2013). We also found the same number of chromosomes (2n = 26) in all species. Moreover, the relative length of the chromosomes was similar among analyzed species and gradually decreased from 5.23 % to 2.78 % of the diploid set in M. satyrus sp. n., from 5.28 % to 2.57 % of the diploid set in M. gardneri , and from 5.24 % to 2.54 % of the diploid set in M. kristensenorum . The Microbuthus from Oman represent a complex with stable karyotypes, as was also documented in Androctonus Ehrenberg, 1828 within the buthid scorpions ( Sadílek et al., 2015).