Megacormus seductus, 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 : 9-16

Megacormus seductus sp. n.

( Figures 1–43 , 56–57, 60, 64–65, 72–73, 78–79, 82, Tables 1–3) http://zoobank.org/urn:lsid:zoobank.org:act:4A7487B6-

78AF-4823-A0F5-58580EF8D89B

Megacormus segmentatus: Sissom, 1994: 265 , 268, 270 (misidentification: specimen and record from Los Tuxtlas).

TYPE LOCALITY AND TYPE REPOSITORY. Mexico, Veracruz, Catemaco Municipality, Los Tuxtlas, Estación de BiologÍa Tropical UNAM, 18°35'02.7''N 95°04'15.7''W, 200 m a. s. l. , FKCP.

TYPEMATERIAL. Mexico, Veracruz, CatemacoMunicipality, Los Tuxtlas, Estación de BiologÍa Tropical UNAM , 18°35'02.7''N 95°04'15.7''W, 200 m a. s. l., broadleaf rainforest on volcanic soil, inside rotten logs and stumps, 23.X.2022, leg. R . Teruel et al., 1♂ (holotype, No. 2460), FKCP , 1♂ 1♀ (paratopotypes, No. 2461), FKCP , 1♂ 2♀1juv.♀ (paratopotypes), RTOC ; Dos Amates , 18°29'39.2''N 95°03'47.6''W, 400 m a. s. l., broadleaf rainforest on volcanic soil, inside rotten stump, 22.X.2022, leg. R . Teruel et al., 3♂ 1♀ (paratypes), FKCP .

ETYMOLOGY. The selected epithet is a Latin word that literally means “one who lives isolated, apart from others”, and highlights the singular geographical occurrence of this species in Los Tuxtlas Massif, removed from the main distribution area of the genus.

DIAGNOSIS. Adult size small for the genus (20–22 mm in males, 24–28 mm in females). Coloration with base light orange to yellowish brown, densely variegated with dark to blackish brown, paler and less spotted on chelicerae, pedipalp, legs and pectines. Pedipalp patella with 22–23 external trichobothria (7 eb, 2 esb, 5 em, 4–5 est, 4 et) and 6–8 ventral trichobothria. Pedipalp fingers with straight proximal dentate margins, without lobe/notch combination in adults of both sexes. 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 2.26–2.29 in males, 2.29–2.32 in females. Telson elongated, narrower than metasomal segment V in both sexes.

SEXUAL DIMORPHISM. Female differing from male by: 1) size larger (23.9–27.8 mm); 2) coloration darker and remarkably more densely infuscate (especially on chelicerae); 3) pedipalps, legs and metasoma slightly longer and slenderer; 4) mesosoma much wider and more convex-sided; 5) sternum larger and parallel-sided; 6) genital papillae absent; 7) pectines much smaller, with teeth shorter, narrower and fewer in number (4–5).

DESCRIPTION (male holotype).

Coloration ( Fig. 1 ) Base color light orange to yellowish brown, paler on chelicerae, pedipalp, 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 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 densely marbled with dark to blackish brown, anterior and lateral margins mostly pale; eyes and ocular tubercles black. Tergites symmetrically and densely marbled with dark to blackish brown, with a large orange spot along midline that defines a pale dashed line all along I–VI, plus a pair of much smaller and fainter posterolateral pale spots on each side that suggest a dark four-stripped pattern for the tergites. Pectines with shaft heavily and irregularly infuscate, but teeth essentially immaculate. Sternites colored and patterned similarly to tergites, but with a solid, narrow black stripe along midline (below ventral median carinae). Legs irregularly marbled with blackish brown, with pale and dark areas distributed in about the same proportion. Metasoma concolorous throughout (i.e., no segments conspicuously darker), densely and irregularly marbled with dark to 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.

Chelicerae ( Fig. 27 ). 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 ( Figs. 7–16 ). Slightly shorter and slenderer than standard for the genus (3.19 times longer than carapace). 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, 4/4 em, 4/5 est, 4/4 et) and 7/7 ventral trichobothria (V); chela manus with 2 dorsal trichobothria (Db, Dt), 10 external trichobothria (3 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 short and robust (length/width ratio = 2.22), almost bare, with all surfaces essentially flat to shallowly convex. Dorsointernal,dorsoexternal, ventrointernal and ventroexternal carinae complete (moderate, coarsely granulose). Tegument densely, roughly and irregularly granulose on dorsal and internal surfaces, coriaceous on external and ventral surfaces. Patella short and robust (length/width ratio = 2.07), almost bare, with dorsal and ventral surfaces flat, external and internal surfaces markedly convex. Dorsointernal, dorsoexternal, external median, ventrointernal and ventroexternal carinae complete (moderately strong, finely granulose to crenulate). Tegument coriaceous, with abundant fine to medium-sized, rough granules scattered all over (coarser and denser dorsally). Inner dorsal spur large, sharp and curved forwards; inner ventral spur small and sharp.

Chela short and robust, but slenderer than standard for the genus (length/width ratio = 3.37). Manus subtriangular in dorsal view (length/width ratio = 1.25, distally narrower) and 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 (moderately strong, finely granulose to crenulate); tegument coriaceous, with a poorly defined reticulate pattern of small, glossy granules scattered all over. Fingers standard for the genus (movable 1.79 times longer than underhand), shallowly curved and sparsely setose, dentition standard for the genus, basal lobe/notch combination entirely absent.

Carapace ( Fig. 27 ). Slightly wider than long (length/width ratio = 0.98), paraboloid in dorsal view. Anterior margin shallowly bilobed, with 2–3 pairs of white macrosetae plus several minor setae; median notch very shallowly V-shaped. Tegument coriaceous, with abundant small granules scattered all over.All carinae indistinct or absent (even the superciliaries). 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 slightly less than one ocular diameter; two pairs of large lateral eyes.

Sternum ( Fig. 28 ). Standard for the genus: type 2, large, longer than wide and hexagonal in shape. Tegument coriaceous, with some medium-sized, round granules irregularly scattered.

Genital operculum ( Fig. 28 ). 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 ( Fig. 28 ). Size and shape standard for the genus: not reaching coxa-trochanter joint of leg IV, subrectangular and moderately setose, anterior area with 4/4 lamellae, median area with 5/6. Tooth count 6/6, teeth swollen, straight and basally not separated; fulcra entirely absent. Basal plate wider than long; anterior margin widely and deeply V-notched medially, posterior margin essentially straight; tegument smooth, glossy to coriaceous and sparsely granulose.

Mesosoma ( Figs. 27–28 ). Tergites almost bare, anterior margin shallowly convex, posterior margin shallowly produced in the median part; median carina very weak and finely subcrenulate on I–VI, submedian and lateral carinae strong and finely serratocrenulate on VII; tegument coriaceous, with abundant small granules scattered all over. Sternites sparsely setose (largely along posterior and lateral margins), posterior margin shallowly concave to widely bilobed; III–VI acarinate, VII with only ventral median carinae perfectly defined, finely granulose to subcrenulate; tegument coriaceous, with abundant coarse and glossy granules; spiracles small, elongate-oval to short slit-like; V with smooth patch large, paraboloid in shape, translucent to yellowish, glossy and slightly bulky.

Metasoma ( Figs. 37–39 ). Size and shape standard for the genus (2.77 times longer than carapace, length/width ratio of segments I–V = 0.64, 0.83, 0.89, 1.23 and 2.27), moderately narrower distally and moderately setose; segments I–III wider than long, IV–V longer than wide; I–III wider than deep, IV–V

Figures 44–61. Megacormus , external pedipalp chela of males (44, 46, 48, 50, 52, 54, 56, 58) and females (45, 47, 49, 51, 53, 55, 57, 59), and external patella of male (60) and female (61). Figures 44–45. M. gertschi . Figures 46–47. M. granosus . Figures 48–49. M. grubbsi . Figures 50–51. M. segmentatus . Figures 52–53. M. xichu . Figures 54–55. M. franckei . Figures 56–57, 60. M. seductus sp. n. Figures 58–59, 61. M. orizaba sp. n

deeper than wide. Segments I–IV with seven complete to almost complete carinae, V with five: all weak, irregularly and finely granulose to crenulate, with distalmost denticle 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 ( Fig. 35 ). Sparsely setose, oval (2.71 times longer than wide, 1.21 times wider than deep); tegument coriaceous, with abundant moderately coarse but weak granules scattered all over and four very shallow longitudinal furrows; distal end of vesicle poorly defined by an obsolete annular ring and vestigial laterodistal shoulders. Aculeus moderately long, sharp and shallowly curved, with tegument glossy.

Legs. Size and slenderness 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, thick but sharp. Claws standard-sized (at least one-third the length of its respective telotarsus) and well-curved.

Hemispermatophore. ( Figs. 64–65 , 72–73 ). Lamelliform. Overall proportions of distal lamina, capsule, truncal flexure, trunk and pedicel standard for the genus. Distal lamina broad with angulate anterior margin, tapering in distal half; excluding crest, lamina width at basal constriction greater than half maximum lamina width. Capsule with moderately broad proximal transverse ridge; proximal dentate process expanded, either subrectangular with 7–9 blunt denticles (No. 2460; both left and right capsules), or lanceolate with 7–10 sharp triangular denticles (No. 2461; both left and right capsules). Distal dentate process broad, laminate, strongly serrated with 13–14 (No. 2460) or 18 (No. 2461) triangular denticles. Basal carina with crown-like structure bearing 4–6 tines. Terminal membrane of sperm duct with numerous fine spicules.

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

By the combination of very small adult size and absolute lack of pedipalp lobe/notch combination in adult males, this species resembles only M. granosus and M. segmentatus , and in fact, it was formerly misidentified as the latter taxon by Sissom (1994). However, M. seductus sp. n. occurs in isolated localities ( Fig. 82 ). The most morphologically similar species can be regarded as M. granosus , which differs in the following morphological characters that are standard in the species-level taxonomy of the genus: 1. Size smaller (14–18 mm in males, 18–23 mm in females). 2. Entire body and appendages densely covered by very short, rigid, white microsetae in addition to ordinary setae. 3. Pectines with shaft not clearly divided into anterior and median areas and lamellae, all fused altogether into a single triangular sclerite (at most with faint incomplete vestiges of sulci). 4. Pectinal tooth count lower (males 3–4, females 1–4). 5. Entire body and appendages with intercarinal granulation noticeably finer and more even. 6. Adults with mesosoma, metasoma and telson remarkably wider and heavier (more conspicuously so in males).

DISTRIBUTION. ( Fig. 82 ). M. seductus sp. n. was found in two localities about 10 km apart from each other, but it may be widespread across Los Tuxtlas area, at least in the relict forest patches. The primary forest has been largely degraded or eliminated all over the area, but several such relicts still persist in the places with steepest slopes and/or privately controlled lands. Los Tuxtlas represents an isolated branch of the Trans-Mexican Neovolcanic Belt, actually its easternmost tip.

ECOLOGICAL NOTES. The types were all collected inside very old, moist, rotten stumps, in very humid places inside low to mid altitude broadleaf tropical rainforest ( Fig. 43 ). Each inhabited stump housed a group of 3–5 individuals of M. seductus sp. n., mostly adults, which after discovery always played dead and remain motionless to confuse a potential predator (a behavior known as thanatosis or catalepsy). It is noteworthy to mention here that live individuals fluoresced very weakly under UV light, to the point that they were barely distinguishable from the background. A similar observation was reported by Soleglad (1976: 286) for live and preserved specimens of M. gertschi . Nevertheless, old exuviae and carcass remains did fluoresce as brightly as many other scorpions, and were readily found while searching in the soil; this allowed us to note that this species also inhabits leaf litter and occurs under rocks partially buried in the litter.

Two females were found carrying litters of young, one at each locality.

In both known localities, M. seductus sp. n. lives sympatrically with the buthid Centruroides gracilis (Latreille, 1804) . At the type locality, it also occurs together with Centruroides flavopictus (Pocock, 1898) and Centruroides catemacoensis Goodman, Prendini, Francke & Esposito, 2021 . In Dos Amates, it also lives sympatrically with the diplocentrid Diplocentrus perezi Sissom, 1991 .

Figures

Figure 43. Megacormus seductus sp. n., habitat at type locality.

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

Figures 1–2. Megacormus seductus sp. n., male holotype (1) and female paratype with a juvenile (2) in vivo habitus.

Figures 3–6: Megacormus seductus sp. n. Figures 3–4. Male holotype in dorsal (3) and ventral (4) views. Figures 5–6. Female paratype in dorsal (5) and ventral (6) views. Scale bars: 10 mm.

Figures 7–16: Megacormus seductus sp. n., male holotype, pedipalp chela dorsal (7), external (8) and ventral (9) views, patella dorsal (10), external (11) and ventral (12) views, femur and trochanter dorsal (13) and ventral (14) views, movable (15) and fixed (16) fingers dentition. Movable finger (15) is under UV light, other figures are under white light.

Figures 17–26: Megacormus seductus sp. n., female paratype, pedipalp chela dorsal (17), external (18) and ventral (19) views, patella dorsal (20), external (21) and ventral (22) views, femur and trochanter dorsal (23) and ventral (24) views, movable (25) and fixed (26) fingers dentition.

Figures 27–34: Megacormus seductus sp. n. Figures 27–28. Male holotype, carapace and tergites I–IV (27) and coxosternal area and sternites (28). Figures 29–34. Female paratype, carapace and tergites I–IV (29), coxosternal area and sternites (30), and left legs I–IV, retrolateral aspect (31–34).

Figures 35–42. Megacormus seductus sp. n. Figures 35, 37–39. Male holotype, telson in lateral (35), metasoma and telson in lateral (37), dorsal (38) and ventral (39) views. Figures 36, 40–42. Female paratype, telson in lateral (36), metasoma and telson in lateral (40), dorsal (41) and ventral (42) views. Scale bars: 10 mm (37–39, 40–42).

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.