Megacormus orizaba, Teruel & Kovařík & Lowe & Šťáhlavský, 2023

Teruel, Rolando, Kovařík, František, Lowe, Graeme & Šťáhlavský, František, 2023, Two new species of the remarkable scorpion genus Megacormus Karsch, 1881 (Scorpiones: Euscorpiidae), Euscorpius 375, pp. 1-22 : 4-9

Megacormus orizaba sp. n.

(Figures 58–59, 61–62, 66, 82, Tables 1–2) http://zoobank.org/urn:lsid:zoobank.org:act:AE1641C9-

4E89-4654-9375-86633841D26D

Megacormus granosus: KovařÍk, 2019: 1 , 11–13, 21–27; figs. 40–41, 51, 90–123 (misidentification).

TYPE LOCALITY AND TYPE REPOSITORY. Mexico, border between Puebla (Tlachichuca Municipality) and Veracruz (Calcahualco Municipality), 2 km west of Atotonilco, northeast slope of Pico de Orizaba [= Citlaltépetl] ; 19°08'50.3''N 97°11'47.6''W, 2400 m a. s. l., FKCP.

TYPE MATERIAL. Mexico, border between Puebla (Tlachichuca Municipality) and Veracruz (Calcahualco Municipality), 2 km west of Atotonilco, northeast slope of Pico de Orizaba [= Citlaltépetl], 19°08'50.3''N 97°11'47.6''W, 2,400 m a. s. l., pine forest, under rocks, 2019, 1♂ (holotype, No. 1621, figs. 40, 51, 90–91, 94–102, 106–108, 111–114, 115– 117, 121 in KovařÍk, 2019) , FKCP, 1♂ 2♀ (paratopotypes, figs. 41, 51, 92–93, 103–105, 109–110, 118– 120, 122 in KovařÍk , 2019) , FKCP, 2.XI.2022 , R. Teruel et al., 2♂ 8♀ 7juvs. (paratopotypes) , RTOC.

ETYMOLOGY. The selected epithet is a Latinized noun in apposition, taken directly from the Spanish toponym of the majestic volcano inhabited by this species.

DIAGNOSIS. Adult size large for the genus (30–34 mm in males, 40–45 mm in females). Coloration entirely blackish, paler and less spotted on chelicerae, pedipalp, legs and pectines. Pedipalp patella with 22–24 external trichobothria (7 eb, 2 esb, 4–5 em, 4 est, 4 et) and 6–8 ventral trichobothria. Pedipalp fingers of adult male with undulate proximal dentate margins, lobe/notch combination moderate. Pectines with shaft clearly divided into areas and lamellae by conspicuous sulci; tooth count 5–6 in males, 4–5 in females. Metasomal segment V length/width ratio 2.37–2.40 in males, 2.38–2.40 in females. Telson elongate, narrower than metasomal segment V in both sexes.

SEXUAL DIMORPHISM. Female differing from male by: 1) size larger; 2) coloration darker and more densely infuscate; 3) pedipalps, legs and metasoma slightly longer and slenderer; 4) mesosoma much wider and more convex-sided; 5) pedipalps, carapace, tergites and metasoma with granulation sparser and finer; 6) genital papillae absent; 7) pectines conspicuously smaller, with lower tooth counts (4–5).

DESCRIPTION (male holotype; Figs. 58, 62, 66 and figs. 40, 51, 90–91, 94–102, 107–108, 111–114, 115– 117, 121 in KovařÍk, 2019; Table 1).

Coloration. Base color light brown, paler on chelicerae, pedipalp manus, legs and pectines, pedipalp chelae and telson with a reddish hue. Cheliceral manus finely and irregularly reticulate with dark brown, denser distally; fingers deeply infuscate. Pedipalps very densely and irregularly marbled with blackish brown, but sparser distally (much denser on femur, sparser on manus), with all carinae deeply infuscate and the base of most trichobothria much paler (yellowish); fingers blackish, with distal third much paler progressively (becoming yellowish at the tip). Carapace symmetrically and very densely marbled with dark to blackish brown, anterior and lateral margins largely infuscate; eyes and ocular tubercles black. Tergites symmetrically and very densely marbled with dark to blackish brown, without any conspicuous pale spots that could suggest a stripped pattern. Pectines with shaft heavily and irregularly infuscate, but teeth essentially immaculate. Sternites colored and patterned similarly to tergites. Legs irregularly and very densely marbled with blackish brown, with few pale areas. Metasoma concolorous throughout (i.e., no segments conspicuously darker), irregularly and very densely marbled with blackish brown and with carinae deeply infuscate. Telson vesicle densely and irregularly marbled with dark to blackish brown, with four faint pale stripes corresponding to longitudinal furrows; aculeus orange, with distal third blackish. In general, the dark pattern is so dense that the entire scorpion looks dull black to the unaided eye, especially when still alive.

Chelicerae. Dentition typical for the genus, teeth short but sharp. Tegument smooth and glossy. Setation very dense ventrally, but essentially lacking dorsally, i.e., reduced to a few macrosetae distally in manus and also along movable finger. Fingers short, robust, evenly curved and subequal in length.

Pedipalps. Size and shape standard for the genus. Trichobothrial pattern C, neobothriotaxic majorante: femur with all three trichobothria (d, e, i) in positions standard for the genus (at basal-most part of segment); patella with 2 dorsal trichobothria (d), one internal trichobothria (i), 21–22 external trichobothria (7/7 eb, 2/2 esb, 4/5 em, 4/4 est, 4/4 et) and 6/7 ventral trichobothria (V); chela manus with 2 dorsal trichobothria (Db, Dt), 11 external trichobothria (4 Eb, 1 Esb, 1 Est, 5 Et, with Et 1 displaced to ventral surface), and 4 ventral trichobothria (with V 4 displaced to external surface); fixed finger with 4 dorsal trichobothria (db, dsb, dst, dt), two internal trichobothria (ib, it) and 4 external trichobothria (eb, esb, est, et).

Femur robust (length/width ratio = 2.34), almost bare, with all surfaces essentially flat to shallowly convex. Dorsointernal, dorsoexternal, ventrointernal and ventroexternal carinae complete (moderate, coarsely granulose). Tegument coriaceous, with abundant fine to medium-sized granules scattered all over, plus abundant medium-sized to coarse, glossy granules irregularly scattered on dorsal surface.

Patella robust (length/width ratio = 2.29), almost bare, with dorsal and ventral surfaces essentially flat, external and internal surfaces markedly convex. Dorsointernal, dorsoexternal, external median, ventrointernal and ventroexternal carinae complete (strong to very strong, coarsely granulose to crenulate). Tegument finely, densely and evenly granulose on internal surface, coriaceous on dorsal, external and ventral surfaces, with abundant medium-sized to coarse, glossy granules evenly scattered all over dorsally and abundant fine and rough granules irregularly scattered all over externally and ventrally. Inner dorsal spur large, sharp and straight; inner ventral spur vestigial, reduced to a conical denticle.

Chela large and robust, standard for the genus (length/width ratio = 2.87). Manus incrassate-oval in dorsal view, medially wider and narrow-oval in lateral view, sparsely setose and prismatic in cross-section; dorsal internal, dorsal marginal, dorsal secondary, digital, external secondary, ventroexternal and ventrointernal carinae complete (strong, coarsely granulose to crenulate); tegument coriaceous, with a clearly defined reticulate pattern of small, glossy granules scattered all over. Fingers somewhat longer than standard for the genus, shallowly curved and sparsely setose, dentition standard for the genus, basal lobe/notch combination moderate (long and not too deep).

Carapace. Almost as long as wide (length/width ratio = 1.03), paraboloid in dorsal view. Anterior margin shallowly bilobed, with 2–3 pairs of white macrosetae plus several minor setae; median notch very shallowly U-shaped. Tegument finely and densely granulose, with abundant medium-sized to coarse granules scattered all over. All carinae indistinct or absent, except for the superciliaries, central medians and posterior medians (weakly, finely granulose and not fused). Furrows: anterior median, central median, posterior median and posterior marginal narrow and moderately deep, fused altogether; posterior laterals narrow and moderately deep; other furrows either absent or undefined. Median ocular tubercle moderately raised, with eyes large and separated by less than one ocular diameter; two pairs of large lateral eyes.

Sternum. Standard for the genus: type 2, large, longer than wide and hexagonal in shape. Tegument densely and finely granulose.

Genital operculum. Medium-sized and prominent, remarkably rhomboidal in shape. Halves neither separated nor fused and almost triangular in shape; tegument smooth and glossy. Genital papillae medium-sized, well-protruding, with tips blunt, round. Pre-pectinal plate apparently absent.

Pectines. Size and shape standard for the genus: not reaching coxa-trochanter joint of leg IV, subrectangular and moderately setose, anterior area with 3/2 lamellae, median area with 3/3. Tooth count 6/6, teeth swollen, straight and basally not separated; fulcra entirely absent. Basal plate wider than long; anterior margin essentially straight, posterior margin widely convex; tegument smooth, glossy to coriaceous.

Mesosoma. Tergites almost bare, anterior margin shallowly sinuose, posterior margin straight to very shallowly produced in the median part; median carina very weak and finely subcrenulate to crenulate on I–VI, submedian and lateral carinae strong and finely serratocrenulate on VII; tegument coriaceous, with abundant small to medium-sized, glossy granules scattered all over (denser posterolaterally). Sternites sparsely setose (largely along posterior and lateral margins), posterior margin shallowly convex to widely bilobed; III– VI acarinate, VII with only ventral median carinae perfectly defined, finely granulose to subcrenulate; tegument on III– VI glossy and minutely punctate, on VII coriaceous, with abundant medium-sized, glossy granules scattered all over; spiracles small and elongate-oval; V with smooth patch large, paraboloid in shape, translucent, glossy and not bulky.

Metasoma. Size and shape standard for the genus (length/ width ratio of segments I–V = 0.65, 0.81, 0.95, 1.26 and 2.37), moderately narrower distally and moderately setose; segment I–III wider than long, IV–V longer than wide; all segments wider than deep. Segments I–IV with seven complete to almost complete carinae, V with five: all strong, irregularly and coarsely dentate to serrate, with distalmost denticles not conspicuously enlarged; lateral inframedians entirely absent or undefined from surrounding granulation on all segments; ventral submedians entirely absent; ventral median carina perfectly defined all along I–V; anal arc weakly granulose; laterodistal lobes of V obsolete, blunt-triangular. Intercarinal tegument coriaceous, with abundant minute and fine granules scattered all over. Dorsal furrow complete, moderately narrow and shallow.

Telson. Sparsely setose. Vesicle oval and somewhat depressed; tegument coriaceous, with abundant minute and fine granules scattered all over and four very shallow longitudinal furrows; distal end of vesicle well-defined by a shallow annular ring and weak laterodistal shoulders. Aculeus moderately long, sharp and shallowly curved, with tegument glossy.

Legs. Somewhat longer and slenderer than standard for the genus, with all carinae weakly granulose to subcrenulate; tegument smooth coriaceous, with dorsal surface of femur sparsely granulose. Prolateral pedal spurs standard-sized to large, thick but sharp. Claws standard-sized (at least one-third the length of its respective telotarsus) and well-curved.

Hemispermatophore. ( Figs. 62 , 66 ). Lamelliform. Overall proportions of distal lamina, capsule, truncal flexure, trunk and pedicel standard for the genus. Distal lamina relatively narrow, nearly unform in width, with straight anterior margin, lacking a basal constriction. Capsule with moderately broad proximal transverse ridge; proximal dentate process elongate or spatulate, slightly broadened, armed with 7–9 irregular, short, blunt or sharp denticles. Distal dentate process moderately broad, laminate, armed 6–7 irregular, small to large, sharp denticles. Basal carina with crown-like structure bearing 6–8 tines. Terminal membrane of sperm duct with numerous fine spicules.

AFFINITIES. The described features distinguish Megacormus orizaba sp. n. from all other species of the genus (see the key below). the validity of M. orizaba sp. n. is confirmed also by DNA analysis implemented by Charles University in Prague (manuscript in preparation).

M. orizaba sp. n. inhabits the same locality as M. granosus , with which it has been confused in the past (see KovařÍk, 2019), but it can be easily distinguished by its larger size (30–34 mm in males, 40–45 mm in females versus 14–18 mm in males, 18–23 mm in females in M. granosus ) and mainly by the presence of a pedipalp lobe/notch in adult males of M. orizaba sp. n. (Fig. 58) which is absent in adult males of M. granosus (Fig. 46). The hemispermatophore of M. granosus has a broad distal lamina with basal constriction ( Fig. 63 , 75 ), similar to that of M. seductus sp. n. ( Figs. 64– 65 ), contrasting with the narrow distal lamina without basal constriction in M. orizaba sp. n. ( Figs. 62 , 66 ).

DISTRIBUTION ( Fig. 82 ). M. orizaba sp. n. is currently known only from the type-locality. Nevertheless, a potential additional locality record may have been given misidentified as M. gertschi by González-Santillán et al. (2017), also from Veracruz State (see below, in Remarks section).

ECOLOGICAL NOTES. The type-specimens were all collected under rocks of various sizes (usually small to medium), in somewhat humid places inside pine forest (fig. 123 in KovařÍk, 2019: 27). The scorpions were usually found on the ground, inside short scrapes excavated by themselves, but as an unusual finding, not less than 10 individuals (mostly juveniles and subadults) were found hanging to the underside of the rocks, frequently at the edges. After the rocks were turned, all scorpions played dead and remain motionless (thanatosis or catalepsy).

At the single known locality, this species lives syntopically with M. granosus , but we observed a very interesting trend. On one hand, M. granosus is widespread throughout the area and occurs in similar numbers both in oak and pine forests, but most commonly in the less densely vegetated areas of the oak forest. On the other hand, M. orizaba sp. n. is entirely restricted to the pine forest and becomes more and more abundant towards its densest core, while at the edge of the pure pine forest (without any oak trees), both species are found together, even under the same rocks.

This is the first time that two species of Megacormus are confirmed to occur together in a same locality. No other scorpion species were found there during the two field trips conducted by the authors to this site.

REMARKS. This species was formerly misidentified as M. granosus by KovařÍk (2019). During the previous field trips (2018–2019) that yielded the specimens used by him for that paper, both species were actually found, but unfortunately, all small specimens (including the authentic M. granosus ) were mistaken for early immatures and not collected. Only during the last field trip (2022), was it noted that there were in fact two distinct species living together and the mistake was discovered.

Conversely, it is odd that González-Santillán & ÁlvarezPadilla (2015) redescribed M. granosus from exactly the same locality, but they did not record the existence of the second, much larger species there. González-Santillán & ÁlvarezPadilla (2015: 75, 77) explicitly stated that their specimens were collected exclusively in the oak forest, where according to our data M. orizaba sp. n. seems not to occur, thus, it apparently went undetected by them.

There is one locality record published as M. gertschi by Soleglad (1976) and González- Santillán et al. (2017), which could well actually belong to its closest-relative M. orizaba sp. n.: 11.2 km southeast of Las Vigas de RamÍrez, in Veracruz State. This site is located roughly 55 km to the north of Atotonilco, in the same mountain system (eastern tip of the Trans-Mexican Neovolcanic Belt) and at similar altitude (2,420 m); even the reference to a “subadult male” ( Soleglad, 1976: 284; González-Santillán et al., 2017: 237) suggests one of the main diagnostic features of M. orizaba sp. n., i.e., the weaker development of the pedipalp finger lobe/ notch combination.

Incidentally, there is some confusion in the previous literature about this character, i.e., it has been incorrectly assumed that a weak lobe/notch combination indicates a subadult male (see, e.g., Soleglad, 1976: 285). Nevertheless, by rearing dozens of specimens from birth to adulthood in captivity, we have confirmed that in all Megacormus species whose male has pedipalp fingers with lobe/notch combination developed, this character state appears only with the terminal ecdysis to adult, i.e., subadult males entirely lack such combination and its fingers resemble those of adult and juvenile females.

Figures

Figure 82. Distribution of Megacormus specimens examined for this review (see Comparative material examined in Methods, Material & Abbreviations section).

Figures 62–65. Hemispermatophores of Megacormus spp. Figure 62. M. orizaba sp. n. 19MD (holotype, No. 1621). Figure 63. M. granosus (No. 2462). Figures 64–65. M. seductus sp. n. 22MA (holotype and paratopotype, Nos. 2460, 2461).Convex views of left hemispermatophores (62, 63) and right hemispermatophores shown in mirror image (64, 65). Scale bars: 500 μm.

Figures 66–77. Hemispermatophore capsules of Megacormus. 66. M. orizaba sp. n. (holotype, No.1621). 67–68. M. gertschi (Nos.1619, 1620).69. M. franckei (paratype, No. 1618).70–71. M. xichu (Nos.1617, 1626).72–73. M. seductus sp. n. (holotype and paratopotype,Nos.2460–2461).74. M. segmentatus (No.1622).75. M. granosus (No.2462).76. M. grubbsi (No.1623).77. M. grubbsi (No.2463).Convex views ofleftcapsules (66, 68–71, 73–75 and 77), and right capsules shown in mirror image (67, 72 and 76).Abbreviations: dpd, distal dentate process; dpp, proximal dentate process; cls, crown-like structure; trd, distal transverse ridge; trp, proximal transverse ridge; tmsd, terminal membrane of the sperm duct. Scale bars: 400 μm.