Male holotype (CNAN-T01315), Michoacán: Coalcomán de Vázquez Pallares municipality: La Nieve (18°49.070'N, 103°02.653'W, 2230‒2260 m a.s.l.), 07-VIII-2002, O. Francke, E. González S. y S. Reynaud colls, determined as Centruroides infamatus ornatus by R. J. Moreno B., 02-VII-2004. Paratypes: 17 ♂♂, 38 ♀♀ Michoacán: Coalcomán de Vázquez Pallares municipality: La Nieve, 10.VII.2006, 2246 m, O. Francke, J. Ponce, M. Córdova, A. Jaimes, G. O. Francke & V. Capovilla, colls: 1 male (peines 22-21) 1 female (18-18). (CNAN-T01316), 3 ♂♂, 5 ♀♀ (CAFBUM S0150), 3 ♂♂ adult, 1 ♂ juvenile, 3 ♀♀ (IESC-3.3796 to. 3.3802). Michoacán: Coalcomán de Vázquez Pallares municipality: La Nieve, 7. VIII. 2002, 2265 m, O. Francke, E. Gonzalez-Santillán & S. Reynaud colls.

Only known from the type locality (Fig. 1).

The proposed name is a patronym honoring Biol. Mario Manuel Romero Tinoco, who has dedicated his life to increasing our knowledge of the “hot land” in Michoacán State, and for his relevant and continued contributions to the people that inhabit those beautiful places.

A medium-sized species belonging to the Centruroides infamatus subgroup (as defined by Ponce-Saavedra and Francke 2019) of the “striped” group. Pectines with 16–18 (mode 18) teeth in females and 20–22 (mode 21) in males (Table 3). Hemispermatophore flagelliform, internal lobe (il) slightly developed, moderately sclerotized and almost straight; medial lobe (ml) scarcely developed but sclerotized; external lobe spiniform hook-like; trunk broad, fusiform and expanded towards the pedal flexure region; truncal flexure is conspicuous; pedicel with margins strongly sclerotized at inner margin that is less sclerotized towards the pedal flexure which is well developed (Fig. 29).

Centruroides romeroi sp. nov. closely resembles C. ruana and C. infamatus, (Quijano-Ravell and Ponce-Saavedra 2016) but it is noticeably smaller (33–45 mm in C. romeroi sp. nov., 63–70.7 mm in C. ruana and 54–66 mm in C. infamatus) having a lower pectinal tooth count and paler coloration pattern. Also, males of C. ruana have pedipalp chelae slightly thicker (Fig. 30b), whereas C. infamatus has subaculear tubercle nearer to the base of the aculeus (Fig. 30k). The most similar species to Centruroides romeroi sp nov. is C. ornatus but the new species differs as follows: It has pedipalps moderately elongated (Fig. 30a); femur with dorsal, external and ventral intercarinal spaces finely and densely granulose and the internal face with many coarser scattered granules, some of which are large and conical; dorsal internal, dorsal external and ventral internal carinae on the manus dentate and well developed and the ventral external carina strong, serrate. Pedipalps of C. ornatus moderately elongated (Fig. 30d); manus oval; femur with intercarinal spaces coriaceous, except dorsally where they are finely granulose; all carinae strong, coarsely granulose to subdentate. Segment V of Centruroides romeroi sp. nov. (Fig. 30a) almost entirely acarinate except for subtle vestiges of dorsal supramedians (basal one-third only), ventral lateral and ventral median carinae. Segment V of C. ornatus (Fig. 30h) with ventral lateral carinae very weakly subgranulose, the submedian carinae absent and ventral median carina weakly subgranulose. Pectinal tooth counts in C. romeroi sp. nov. male 18–22, female with 16–21 teeth, whereas C. ornatus males have 19–24 teeth, females 17–23. Basal pectinal plate of C. romeroi sp. nov. with anterior margin with a deep, narrow anteromedian notch, whereas on C. ornatus the anterior margin is almost straight, with small median V-shaped notch (Fig. 31d). Also, the distribution of C. ornatus is endemic to the Transverse Volcanic Belt whereas C. romeroi sp. nov. is distributed only in the Coalcomán mountain range which is part of the western-most region of the Sierra Madre del Sur (Fig. 1).

(Figs 2–20). A typical “striped scorpion”, basically yellow, paler ventrally (Figs 2–5). Carapace with a broad dark brownish band that runs from the lateral eyes to the posterior median carinae, except on median furrow, two patches lateral to ocular tubercle, the ocular lateral furrows and the posterior median furrow, all which are immaculate (Fig. 6). Ocular tubercle and area around lateral eyes intensely infuscate. Lateral margins pale brown. Lateral submargins mostly immaculate, with vestigial brown pigment. Posterior margin with two short dark lines from which the tergites stripes originate. Mesosoma dorsally with two longitudinal blackish stripes on tergites I–VI, separated by a slightly narrower pale stripe; on VII the dark stripes become diffuse (Fig. 7). Median longitudinal carina immaculate on all tergites. Pedipalps mostly immaculate, chelae ventrally vestigially infuscate; the fingers have the same color as the manus (Figs 8, 9). Metasoma dorsally immaculate, ventrally and laterally with vestigial pigments on segments I–IV, and immaculate on V and telson (Figs 2–5, 10). Legs immaculate.

Carapace. Anterior margin with median notch broadly “V” shaped, reaching the level of the posterior margin of the first pair of lateral eyes, weakly crenulate and scarcely setose; three pairs of lateral eyes subequal in size (Fig. 6). Lateral areas feebly granulose, margins finely granulate. Ocular tubercle smooth. Central pigmented area with medium-sized granules, but finely granulose around the ocular tubercle (Fig. 6). Posterior margin straight, granulose, with medium-sized granules and a shallow median indentation (Fig. 6). Carinae: anterior medians indistinct; superciliary crest smooth, with obsolete broad granules (Fig. 6); posterior medians well developed, granulose. Furrows: anterior median, median ocular, posterior median, and posterior marginal wide and moderately deep; laterals ocular narrow; posterior laterals wide, with disperse small granules; central laterals vestigial (Fig. 6).

Mesosoma. Tergites with moderate median longitudinal carina (Figs 7, 11); submedian and lateral carinae on VII strong and serrate. Pigmented areas are covered by small to medium-sized granules (Fig. 7). Sternites sparsely setose, spiracles oblique and slit-like; III – VI acarinate; III with a median triangular area which is smooth and glossy, and two lateral areas which are densely and finely granulose (Fig. 12); IV – VI with integument smooth and glossy, each with four short and smooth posterior carinae, with the submedian pair indistinct on IV – V; V with some coarse punctures medially, without translucent whitish patch; VII with two pairs of long and moderately to strongly costate to subcrenulate submedian and lateral carinae, intercarinal spaces very finely and densely granulose (Fig. 12).

Sternum type 1, triangular, very finely granular, with two long, median subdistal macrosetae; posterior depression long, wide and deep (Fig. 13).

Genital operculum (Fig. 13) medium-sized (its width is slightly larger than the sternum length); each valve subtriangular, with four macrosetae and some shorter setae. Genital papillae do not protrude from the posterior margin of the valves. Prepectinal plate moderately sclerotized, with anterior margin concave.

Pectines. Tooth count 21/22. Basal plate rectangular, anterior margin almost straight, with small median V-shaped notch, posterior margin straight (Fig. 13).

Metasoma. Moderately elongated and not incrassate distally (Figs 2, 3, 10). Intercarinal spaces coriaceous, with scarce minute granules. Segments I–IV with the following carination: dorsal laterals, lateral supramedians and lateral inframedians (on I only) well developed, serrate, the dorsal lateral carinae become gradually stronger and dentate distally on each segment, mainly on II – III; ventral laterals and ventral submedians well developed, finely granulate and subserrate. Segment V rounded in cross-section, almost entirely acarinate except for subtle vestiges of dorsal supramedians (basal one-third only), ventral lateral and ventral median carinae (Fig. 14). Telson with vesicle slightly elongated (length/width ratio = 1.78, depth/width ratio = 1.00) and coriaceous; ventral median carina vestigial; subaculear tubercle short, widely conical and somewhat distant from the base of aculeus, which is shorter than vesicle and moderately curved (Fig. 15), moderately setose. Vesicle incrassate oval (1.81 times longer than wide, 1.07 times wider than deep), integument coriaceous; ventral median carina vestigial, ending in a small subaculear tubercle, widely conical, not particularly close nor separated from base of aculeus. Aculeus strongly curved, shorter than vesicle.

Chelicerae with dentition typical for the genus (Fig. 16). Tegument very finely and densely granulose, dorsodistal portion of manus with coarse and glossy granules arranged transversally, defining a depressed area. Setation very dense ventrally, but essentially lacking dorsally, except for five rigid macrosetae on depressed area of manus: two anterior (the shortest), two posterior and one in the center on a rounded and elevated base (Fig. 16).

Pedipalps orthobothriotaxic A-α; moderately elongated (length/width ratio of femur and patella = 4.8 and 3.6, respectively). Femur with dorsal, external and ventral intercarinal spaces finely and densely granulose (Fig. 17); internal face with with many scattered coarser granules, some of which are large and conical; carinae: dorsal internal, dorsal external and ventral internal well developed, dentate; ventral external carina strong, serrate. Patella sparsely setose, with intercarinal spaces finely and densely granulose; dorsal, external and ventral carinae crenulate to subcrenulate, internal surface with five very large and sharp tubercles (Fig. 18). Hand evenly ovate (Figs 9, 19, 20), 1.1 times as wide as the patella; intercarinal spaces coriaceous; ventral accessory carina and external secondary carina indistinct, with obsolete small granules (Figs 19, 20); digital carina feebly to moderately granulose; dorsal secondary carina and dorsal external carina poorly developed, subgranulose; ventral external carina and ventral internal carina strong and rather subcrenate. Fixed finger long, slender and evenly curved, with a basal notch, eight principal rows of denticles, rows 3 to 7 are flanked by two outer accessory denticles and two inner accessory denticles, whereas in row 8 there is no outer accessory denticle nor an inner accessory denticle; movable finger with eight principal rows of denticles and one apical subrow of three denticles (Fig. 20), basal lobe moderately developed, rows 3 to 7 are flanked by two outer accessory denticles and two inner accessory denticles, whereas row 8 has a single outer accessory denticle and one inner accessory denticle.

Legs. Slender, with carinae granulose to subserrate and intercarinal tegument coriaceous to minutely granulose. Prolateral and retrolateral pedal spurs strong and somewhat curved in all legs. Ventral surface of tarsomere II densely covered by long macrosetae irregularly arranged into two longitudinal, broad, dense rows converging basally. Claws rather short and curved.

Differs from males as follows: color pattern somewhat darker. Metasoma and pedipalps shorter and robust (Figs 21–28, Table 2). Telson with vesicle more globose (Fig. 28). Pectines with 16–21 (mode 18, N = 90) teeth in females, whereas in males it is 18–22 (mode 21, N = 46) (Table 3). Basal plate of the pectines with anterior margin faintly concave and the posterior margin slightly convex (Fig. 25). Genital papillae absent.

Pectinal tooth count varies among both sexes (Table 3). Adult males of the type series comprise three size categories and range from 33 to 45 mm in total length. Females: 34–40 mm (Table 1). Most males have pedipalp manus as wide as the patella.

La Nieve (2030 to 2260 m a.s.l.) belongs to the Coalcomán Range, the predominant vegetation is pine forest, and the climate is temperate sub humid (Cw). The scorpions were collected at night, with portable U.V. lights, under stones and fallen rotten trees, under bark of Pinus sp., in the yards and walls of the local school and houses of the village. During the collection the temperature and relative humidity of the air were 10‒12 °C and 90%, respectively. Centruroides romeroi sp. nov. is sympatric with Vaejovis coalcoman Contreras-Félix & Francke, 2014.

The 16S mitochondrial marker was used successfully by several authors for delimiting several species in the genus Centruroides such as the cryptic species C. exilicauda (Wood) and C. sculpturatus (Ewing) (Gantenbein et al. 2001), and C. limpidus Karsch and C. tecomanus Hoffmann (Ponce-Saavedra et al. 2009), and for delimiting new species such as C. ruana which was separated from C. ornatus and C. infamatus (Quijano-Ravell and Ponce-Saavedra 2016). For this reason, in addition to the morphological diagnostic characters, a molecular analysis using sequences of the mitochondrial gene mRNA 16S was carried out.

The results showed stronger genetic divergence (measured as p-distance and the Jukes-Cantor model) between the population of C. romeroi sp. nov. and populations of C. ornatus at two localities of the municipality of Morelia, Michoacán (p-distance = 0.076–0.079), and with two populations at Chapala, Jalisco (p-distance = 0.093–0.098), with one population of C. balsasensis (p-distance = 0.128) rather than to C. infamatus from two localities of Michoacán (p-distance = 0.463) and with the type population of C. ruana (p-distance = 0.049). These differences were consistent both using p-distance and the Jukes-Cantor model (Table 4). The trees obtained by the different phylogenetic hypothesis models were topologically consistent; the bootstrapping consensus tree is showed in the Figure 32. The topology of the consensus tree shows that C. romeroi sp. nov. appears most related to C. ruana in a clade formed by the populations of C. infamatus and C. ornatus (Fig. 32). The results are consistent with the geographic distribution of the new species, which lives in the Coalcomán mountain range in the westernmost region of the Sierra Madre del Sur, with its nearest species C. ruana, that inhabit the western region of Balsas Depression, while the other two clades are species occur in the Transverse Volcanic Belt (Fig. 1).

These molecular results support our decision of considering the Coalcomán population as an isolated and taxonomically valid species.