The male of Megacormus granosus (Gervais, 1844) with comments on its hemispermatophore (Scorpiones, Euscorpiidae)

Abstract The male of Megacormus granosus is described for the first time and the female redescribed. A homology scheme proposed recently is applied to hemispermatophore structures. The specimens were collected in an oak forest from Pico de Orizaba Volcano at an average altitude of 2340 m. All adult males were collected by pitfall traps, whereas all adult females and both sex immatures were collected using Berlese funnels, suggesting that males are comparatively more mobile within the leaf litter layer, probably due to mating season.


Introduction
The Mexican genus Megacormus (Karsh, 1881) is comprised of four species, M. granosus (Gervais, 1844); M. segmentatus Pocock, 1900;M. gertschi Díaz Nájera, 1966 andM. grubbsi Sissom, 1994. All species of Megacormus are restricted to the slopes of the Sierra Madre Oriental and the costal lowlands of the Gulf of Mexico, ranging in altitude from 300 m to over 2300 m. They prefer habitats with high relative humidity such as oak, oak-pine and evergreen tropical forest, and are found in these communities within the leaf litter, outcrop crevices, decaying logs or under rocks. Their distribution includes the states of Hidalgo, Oaxaca, Puebla, Querétaro, San Luis Potosí, Tamaulipas, and Veracruz (Sissom 2000).
Megacormus granosus was originally described as a species of Scorpio Linnaeus, 1758 from a single female (Soleglad 1976), but its description and illustrations became obsolete as more scorpion diversity was discovered. The only character used to define this species was the dense granulation on the cuticular dorsal surfaces (Figures 1, 2). The second described species of the genus was M. segmentatus Pocock, 1900, distinguished by the presence of a distinct furrow between the pectinal marginal and median lamella, which is absent in M. granosus. Subsequently M. segmentatus was considered as a subspecies of M. granosus by Hoffmann (1931). The third species, M. gertschi, was diagnosed by having a greater number of trichobothria on the patella prolateral surface and the presence of scalloping on pedipalp chela fingers. The first comprehensive revision of these taxa was done by Soleglad (1976), who recognized three species by reverting M. granosus segmentatus status to its original designation as M. segmentatus. Sissom (1994) added a fourth species and illustrated for the first time the hemispermatophores of M. grubbsi and M. segmentatus, but to date the hemispermatophore of M. granosus has never been documented. Although Sissom's (1994) extended descriptions, diagnoses and key to the species of Megacormus are in use, variation of diagnostic characters, i.e. trichobothrial counts, pectinal counts, etc., are not documented appropriately due to the paucity of specimens in scientific collections, except perhaps for M. gertschi (Sissom 1994) and in this contribution M. granosus.
The hemispermatophore constitutes one of the most informative character systems in suprageneric phylogenetic studies, at least in Bothriuridae Simon, 1880 and Vaejovidae Thorell, 1876(Mattoni et al. 2011, González-Santillán and Prendini 2014; it has shown little value in diagnosing species of Euscorpiidae (Jacob et al. 2004) or Diplocentridae (Santibañez-López and Francke 2013) however. These results are congruent with the prediction of Song and Bucheli (2010) and the hypothesis of Peretti (2010), that the complex interaction of genitalic functional units is informative at several levels of the phylogeny and taxonomic hierarchy, but structures in related species that perform the same function tend to have the same selective pressure, thus presenting little variation. The hemispermatophore of the genus Megacormus is putatively informative (Sissom 1994: p. 269, figures 8-10), but its microstructure has never been studied in detail.
The unsatisfactory working terminology and concomitant absence of homologies in the hemispermatophore of the Order Scorpiones have promoted a plethora of nomenclatures, hindering the correct interpretation of homologies (Lamoral 1979, Stockwell 1989. Recently, González-Santillán and Prendini (2013Prendini ( , 2014 consolidated a terminology used by previous authors (Stockwell 1989, Sissom 1994, upon which they established a homology scheme for the hemispermatophore of the subfamily Syntropinae (Vaejovidae). In this contribution we extend that terminology and homologies to the scorpion family Euscorpiidae Laurie, 1896, when possible, applying it to the hemispermatophore of M. granosus.

Methods
All scorpions were collected by sifting leaf litter processed with Berlese funnels and pitfall traps. Specimens are deposited in the Laboratorio de Aracnología de la Facultad de Ciencias, Universidad Nacional Autónoma de México (UNAM), Mexico. Measurements in mm were taken with an ocular micrometer. Illustrations were produced with a Nikon SMZ 1000 dissecting stereomicroscope and a Nikon Eclipse E200 with a camera lucida. Photomicrographs were taken with a digital camera Nikon DS-U3 under LED illumination and Ultraviolet (UV) light using a 20W Techno Lite® bulb mounted in a desktop stand lamp. Hemispermatophores were digested with pancreatine (Alvarez-Padilla and Hormiga 2007), cleared with clove oil and mounted in temporary slides for illustration (Coddington 1983).
Chelicerae: Manus dorsal surface smooth, lustrous, with three macrosetae distally, decreasing in size from median to lateral surface. Movable finger, retrolateral margin with subdistal and medial denticles triangular, subequal; distal and basal denticle slightly larger; prolateral margin with three smaller, triangular, subequal denticles, situated in distal half of the finger; retrolateral distal finger size half of prolateral distal finger. Fixed finger margin with three denticles, proximal two adjacent and distal separate; distal denticle elongate and sharp ( Figure 7); ventral surface of manus, fixed and movable finger with an interspaced tuff of setae with curved tips. Serrula absent. Carapace: Length equal to 0.9 times the posterior width. Surface shagreened, with enlarge scattered granules covering entire surfaces (Figure 8). Distal margin with two pairs of macrosetae; emarginated, bilobed, with a shallow median notch, with extreme lateral sides curving placing lateral ocelli in a laterofrontal position. Two pairs of lateral ocelli of equal size, lateral ocular carinae strong, costate-granular. Median ocular tubercle raised, situated in anterior half of carapace. Superciliary carinae strongly (♀) or weakly (♂) granular, lower than median ocelli. Anteromedian sulcus deep and broad, with scattered granules; posteromedian, proximal half with a granular carina and distal half with a deep and broad depression; anterolateral, deep and narrow; posterior transverse shallow.
Coxosternal region: Sternum pentagonal, subequilateral, length equal to 0.8 times the width, with five to ten pairs of microsetae. Median sulcus of sternum with anterior and posterior margins broadened, moderately deep (♂), or very deep (♀). Coxa IV two and half times longer than coxa II. Coxae I-IV surfaces with scattered granules and margins densely granular; coxa II, prolateral subproximal margin with three oblique slit-like structures, adjacent to a moderate (♀) or low (♂) granular protuberance; coxae II-IV, prolateral carinae strongly granular (Figures 20, 21).
Pedipalps, Femur prolateral, dorsal and retrolateral intercarinal surfaces shagreened (Figure 9), ventral surface with a cluster of fine granules medially. Dorsal prolateral, dorsal retrolateral, ventral prolateral and dorsal prolateral carinae complete, irregularly granular; retrolateral dorsosubmedian complete, weak proximally, becoming strongly granular distally; retrolateral ventral and ventral median carinae vestigial, reduced to few granules proximally; ventral retrosubmedian partial, with a scattered enlarged granules on proximal half; prolateral ventral vestigial, one or two median granules;  (7), 1 mm (8). prolateral ventrosubmedian partial, with enlarged granules on proximal fifth. Patella width 1.5 times greater than femur width. Dorsal intercarinal surfaces shagreened, prolateral, retrolateral, and dorsal sparsely finely granular. Dorsal prolateral, dorsal retrolateral, ventral prolateral, ventral retrosubmedian, and retrolateral median complete, granular; retrolateral dorsosubmedian absent; prolateral process reduced, expressed as a spiniform enlarged tubercle, prolateral median carina vestigial, expressed by one or two median granules (Figures 10-13). Chela length 1.9 times greater than femur and patella, width 1.6 times greater than patella and 1.1 than femur. Dorsal intercarinal surfaces shagreened, a dense field of minute and coarse granules subdistally, other surfaces with scattered minute and coarse granules. Dorsal retrolateral carina complete, strongly granular, extending to proximal four-fifths of the fixed finger, becoming weaker and smooth distally; dorsal retrosubmedian accessory vestigial, irregularly gran- ular, restricted to trichobothrium Dt; dorsal median and dorsal retrosubmedian with an enlarged proximal tubercle, complete, irregular, granular forming two rows proximally, converging into a single row distally; prolateral dorsal, dorsal prosubmedian and dorsal prolateral, fused, irregular, with five to seven scattered granules proximally, minute and coarse granules medially, and coarse granules extending to fixed finger to the extent of trichobothrium dsb; retrolateral dorsal partial, minute granules on median two quarters; retrolateral dorsosubmedian vestigial, restricted to distal short row of coarse granules between trichobothria Et 4 and Et 5 ; retrolateral median complete, strongly granular, ending at the level of trichobothria Et 3 and Et 4 ; retrolateral subventral accessory and retrolateral subventral vestigial, restricted to a distal short row of coarse granules converging to trichobothrium Et 2 , commonly merging to ventral retrolateral carinae; retrolateral ventral partial, irregular, with minute granules restricted by trichobothria Esb and Est; ventral retrolateral complete, strongly granular, in some specimens forming a ring of granules around trichobothrium V 4 ; ventral median partial, strongly granular proximally, becoming weak medially and merging with a field of granules distally, ventral retrolateral and ventral median forming an acute angle proximally, becoming parallel medially to distally; ventral prolateral and prolateral ventral complete, merging to a low tubercle proximally, multiple rows of granules curving to prolateral condyle distally; prolateral ventral accessory partial, restricted to midpoint of the manus as a multiple row of minute and coarse granules, prolateral median partial, irregular, coarse granules row restricted to proximal half (Figures 14-17). Pedipalp fixed and movable fingers: notches, lobes, and gap when fingers closed absent; dentate margin sublinear, compound, with multiple rows of prolateral, median and retrolateral denticles; prolateral, prolateral accessory, retrolateral and median denticles aligned in an oblique row angling retrolaterally in position III-VI. Fixed finger median row comprising six or seven denticle subrows with, commonly two, occasionally one denticle in position I, four to six in position II-VII; flanked by a two-or three-denticle retrolateral accessory median subrow, absent in position I; median subrows divided by six or seven retrolateral denticles, indistinguishable from median subrows' denticles in position VII/VIII-X; median accessory subrows divided by five or six subpaired retrolateral accessory denticles, absent on I and undistinguishable from median accessory denticles subrows on VII/VIII-X; flanked by six or seven prolateral denticles and a subpaired prolateral accessory denticles in position III-VI, absent on I and II, vestigial to absent on VII-X. Movable finger median denticle row comprising six or seven median denticle subrows, zero to one in position I, three to seven in positions II-IX, zero on X; flanked by a two-or three-denticle median accessory denticles subrows, absent in position I; median subrows divided by seven to eight retrolateral denticles, indistinguishable in position IX and X, and median accessory subrows divided by six to seven subparied retrolateral accessory denticles, absent in position I, undistinguishable in position VII-X; flanked by nine prolateral denticles, position III-X subparied by prolateral accessory denticles, lower and less defined in positions VIII-X (Figures 18, 19).
Hemispermatophore: Distal lamina 1.1 times the length of trunk; tapering distally, basal constriction well-developed (Figures 26-28). Capsule's dorsal and ventral troughs strongly sclerotized, merging into a complete, thick, transverse plate, dividing lamina and trunk ( Figure 28). Marginal terminus of dorsal and ventral troughs with a spiculate processes with 25 and 24 irregular spines [in part Sissom's (1994) accessory lobes], respectively. Hemi-mating plug gelatinous. Sperm duct formed by a spiculecoated membrane (sensu Jacob et al. 2004) connected to the spiculate processes of the dorsal and ventral troughs and to the crown-like process (sensu Jacob et al. 2004). Trunk broad proximally, tapering distally; crown-like process relatively long, with row of six to eight irregular spinules on the margin; truncal flexure and dorsal axial carinae well-developed (Figures 26-28).
Distribution. Megacormus granosus has been reported in the vicinities of the National Park Pico de Orizaba, on the slopes of the Trans-Mexican Volcanic Belt facing the Gulf of Mexico, and between Orizaba and Huatusco, Veracruz.
Ecology. All adult males were collected by pitfall traps, suggesting high motility within the leaf litter. They were particularly abundant in the May 2012 expedition. This behavior in males and the period of the year may be related to the mating season of the species. All adult females and immatures of both sexes were collected exclusively using Berlese funnels, suggesting these are comparatively less mobile. A total of 72 Berleses and 180 pitfalls were used to sample two hectares, of which 18 (25%) and 11 (5%), caught 18 and 9 specimens respectively. These yields are consistent with low population density of this species; adult males are particularly rare. The habitat of, and behavior exhibited by, this species as well as its cryptic morphology (color resembling substrate; relative small size) are congruent with a humiculous ecomorphotype (Prendini 2001).
Remarks. The catalog of the scorpions of the world (Fet et al. 2000) indicates that the location of M. granosus type material is either unknown or lost. It is important to investigate the whereabouts of Gervais' unique specimen to verify the holotype, or failing this, to designate a neotype. Workable keys to the species of Megacormus are provided in Sissom (1994). The genus Megacormus is under revision by O.F. Francke (per. comm.).

Discussion
The illustrations of the M. granosus hemispermatophore presented in Figures 26 and  27 are congruent with that of Stockwell (1989: p. 381, figure 217), but differ from that of Sissom (1994: p. 269, figures 8-10), who illustrate accessory lobes associated to the sperm duct (Sissom's acc, figure 8). According to our findings, the accessory lobes are the termini of both the dorsal and ventral trough margins with a spiculate process (Figures 26, 27) and are not independent lobes as suggested by Sissom's illustration ( Figure 28). Furthermore, the basic conformation of the sperm duct, with the spiculecoated membrane and the crown-like process, appears to be uniform in these species.
Although intra-and inter-specific comparative work is needed, we hypothesize that the capsular region of the hemispermatophore of Megacormus might carry little information to diagnose species of the genus, as demonstrated in other species complexes (Jacob et al. 2014, Santibañez-López andFrancke 2010) and predicted by other studies (Song andBucheli 2010, Peretti 2010).