Sexual dimorphism and functional allometry in scorpions: A comparative study from a neotropical species.

Sexual dimorphism (SD), the divergence of secondary sexual traits between males and females within a species, can arise from diverse evolutionary forces, such as natural selection, mate choice, and intrasexual competition. Allometric scaling patterns of dimorphic traits are related to their functional roles and the different selective pressures that affect each sex. Generally, traits that threaten rivals involved in intrasexual competition tend to exhibit the highest allometric slopes. Conversely, non-sexual traits often display isometric scaling, while genitalia and traits in direct contact between the sexes during courtship and copulation typically show hypoallometry. A good approach to study patterns of SD and allometry is to complement interspecific studies with analyzes of case studies, where the functional aspect is known in detail. Here, we review the occurrence of SD and evaluation of allometry in the Order Scorpiones, allowing us to compare general trends in a broader comparative framework within the group. In addition, we examined SD and allometric slopes of multiple traits (including somatic traits used in sexual and non-sexual interactions, as well as genitalia) in adult individuals of the scorpion Timogenes elegans (Scorpiones, Bothriuridae). We found that at an interspecific level there was a variation in SD between species and morphological traits, with most traits showing a male-biased SD, except for the chelicerae, which were found to be wider in females. Regarding SD studies, we found relatively few reports of functional allometry showing differences in allometric patterns between species. The results in T. elegans follow some of the general patterns found in other scorpions. We found hypoallometry in genital traits and hyperallometry in the pedipalps of both sexes, with steeper allometric slopes observed for pedipalp height in males. These results suggest that genital traits are under stabilizing selective pressure, while pedipalps in both sexes may be under natural and sexual selective pressure. Understanding allometric patterns and their relationship to function in scorpions provides significant insights into the evolutionary pressures driving the divergence of morphological traits used in both sexual and non-sexual contexts.

Late Ordovician eurypterid preserves oldest euchelicerate musculature in pyrite.

Pyritization of soft tissues of invertebrates is rare in the fossil record. In New York State, it occurs in black shales of the Lorraine Group (Late Ordovician), the best-known example of which is Beecher's Trilobite Bed. Exceptional preservation at the quarry where this bed is exposed allowed detailed examination of trilobite and ostracod soft-tissue anatomy. Here, we present the first example of a eurypterid (sea scorpion) currently ascribed to Carcinosomatidae from this deposit that also preserves the first evidence for mesosomal musculature in eurypterids. This specimen demonstrates that eurypterid musculature can be preserved in pyrite and evidences the oldest example of euchelicerate muscles within the fossil record. Sulfur isotope data illustrate that pyrite rapidly replicated muscle tissue in the early burial environment, prior to the pyritization of biomineralized exoskeleton and cuticular trilobite limbs. This discovery therefore expands the limited fossil record of euchelicerate musculature, while extending the taphonomic scope for preservation of detailed internal structures, more broadly, within arthropods.

Convergent evolution of giant size in eurypterids.

Eurypterids-Palaeozoic marine and freshwater arthropods commonly known as sea scorpions-repeatedly evolved to remarkable sizes (over 0.5 m in length) and colonized continental aquatic habitats multiple times. We compiled data on the majority of eurypterid species and explored several previously proposed explanations for the evolution of giant size in the group, including the potential role of habitat, sea surface temperature and dissolved sea surface oxygen levels, using a phylogenetic comparative approach with a new tip-dated tree. There is no compelling evidence that the evolution of giant size was driven by temperature or oxygen levels, nor that it was coupled with the invasion of continental aquatic environments, latitude or local faunal diversity. Eurypterid body size evolution is best characterized by rapid bursts of change that occurred independently of habitat or environmental conditions. Intrinsic factors played a major role in determining the convergent origin of gigantism in eurypterids.

Scorpions trapped in amber: a remarkable window on their evolution over time from the Mesozoic period to present days

This synoptic review aims to bring some general information on fossil scorpions, namely those trapped in amber - fossilized resin - ranging from Lower Cretaceous through the Palaeocene and up to the Miocene. The question to be addressed is how the study of these fossils can be connected with possible present scorpionism problems. A precise knowledge of these ancient lineages provides information about the evolution of extant lineages, including the buthoids, which contain most known noxious species. Among the Arthropods found trapped in amber, scorpions are considered rare. A limited number of elements have been described from the Late Tertiary Dominican and Mexican amber, while the most ancient Tertiary amber from the Baltic region produced more consistent results in the last 30 years, primarily focusing on a single limited lineage. Contrarily, the Cretaceous amber from Myanmar, also called Burmite, has yielded and continues to yield a significant number of results represented by several distinct lineages, which attest to the considerable degree of diversity that existed in the Burmese amber-producing forests. As in my previous similar contributions to this journal, the content of this note is primarily addressed to non-specialists whose research embraces scorpions in various fields such as venom toxins and public health. An overview knowledge of at least some fossil lineages can eventually help to clarify why some extant elements associated with the buthoids represent dangerous species while others are not noxious.(AU)

Biomechanical analyses of pterygotid sea scorpion chelicerae uncover predatory specialisation within eurypterids.

Eurypterids (sea scorpions) are extinct aquatic chelicerates. Within this group, members of Pterygotidae represent some of the largest known marine arthropods. Representatives of this family all have hypertrophied, anteriorly-directed chelicerae and are commonly considered Silurian and Devonian apex predators. Despite a long history of research interest in these appendages, pterygotids have been subject to limited biomechanical investigation. Here, we present finite element analysis (FEA) models of four different pterygotid chelicerae-those of Acutiramus bohemicus, Erettopterus bilobus, Jaekelopterus rhenaniae, and Pterygotus anglicus-informed through muscle data and finite element models (FEMs) of chelae from 16 extant scorpion taxa. We find that Er. bilobus and Pt. anglicus have comparable stress patterns to modern scorpions, suggesting a generalised diet that probably included other eurypterids and, in the Devonian species, armoured fishes, as indicated by co-occurring fauna. Acutiramus bohemicus is markedly different, with the stress being concentrated in the proximal free ramus and the serrated denticles. This indicates a morphology better suited for targeting softer prey. Jaekelopterus rhenaniae exhibits much lower stress across the entire model. This, combined with an extremely large body size, suggests that the species likely fed on larger and harder prey, including heavily armoured fishes. The range of cheliceral morphologies and stress patterns within Pterygotidae demonstrate that members of this family had variable diets, with only the most derived species likely to feed on armoured prey, such as placoderms. Indeed, increased sizes of these forms throughout the mid-Palaeozoic may represent an 'arms race' between eurypterids and armoured fishes, with Devonian pterygotids adapting to the rapid diversification of placoderms.

A Comparative Morphometric Study on Odontobuthus bidentatus and Odontobuthus doriae (Scorpionida: Buthidae) in Iran.

Scorpions are one of the most venomous animals which cause serious public health problems. The sting of scorpions can sometimes be fatal depending on the scorpion species involved. So far, sixty-six (66) scorpion species have been identified in Iran. Annually, about 40-50000 cases of scorpionism are reported in Iran. Odontobuthus doriae and O. bidentatus are among the most medically important scorpion species in Iran, and they are very similar to each other in coloration, carination, and trichobotrial patterns. This morphometric study aimed to compare some of the important morphological characteristics in order to identify the key differences between these two species. A total of 45 morphological characters were measured using calipers and stereomicroscope, and 55 morphological characters and ratios (relative of length to width ratio of morphological characters of scorpions) were analyzed. The independent sample t-test in SPSS software (version 24) was used for the statistical analyses in this study. The mean total length, carapace width, length of fixed and moveable fingers, and chelicerae length of O. doriae were greater than those of O. bidentatus in our study area. The morphological measurements displayed a clear distinction between O. doriae and O. bidentatus in our study area; therefore, they can be used as morphological identification keys for distinguishing between these two species.

Burrowing into the forest: Phylogeny of the Asian forest scorpions (Scorpionidae: Heterometrinae) and the evolution of ecomorphotypes.

Asian forest scorpions (Scorpionidae Latreille, 1802: Heterometrinae Simon, 1879) are distributed across South and Southeast Asia. All are fossorial, constructing burrows under stones or in open ground, in habitats differing in precipitation and vegetation cover, from rainforests and tropical deciduous forests to savanna and scrubland. The systematics of these scorpions has long been confused due to bad taxonomy and the absence of a phylogenetic framework. Although the monophyly of the group was previously confirmed as part of broader phylogenetic analyses based on exemplar species, the only quantitative analysis of species-level variation to date was based on overall similarity. This contribution presents the first species-level phylogenetic analysis of Asian Scorpionidae, based on 186 morphological characters and 4188 aligned base-pairs of DNA sequence data from two nuclear and three mitochondrial loci for 132 terminals including all 41 ingroup species and four outgroup species. Simultaneous analyses of the morphological and molecular datasets with parsimony, Maximum Likelihood and Bayesian Inference provided the framework for a revised classification presented elsewhere. In order to understand how adaptation following dispersal into new habitats has driven the morphological diversification of Asian forest scorpions, species were scored for 10 characters concerning morphology and burrow architecture, which contributed to an ensemble index of adaptation to habitat aridity. Species were classified into three ecomorphotypes based on the index, and ancestral state reconstruction of ecomorphotypes performed on the phylogeny. A pattern was recovered in which lineages and species occurring in different habitats on a continuum from wet (evergreen forest) to dry (savanna, scrubland) exhibited characters presumed to be adaptive and hence responsible for driving scorpion diversification.

Transcriptomic and proteomic analyses of venom glands from scorpions Liocheles australasiae, Mesobuthus martensii, and Scorpio maurus palmatus.

Scorpion venom contains a cocktail of differing peptides and proteins. Previous studies focused on the identification of species-specific components in scorpion venoms, and whether there could be peptides and/or proteins conserved in the venom gland of a scorpion ancestor has been rarely investigated. Here, using a combination of transcriptomic and proteomic approaches, putative conserved toxins from the venom glands of scorpions Liocheles australasiae, Mesobuthus martensii, and Scorpio maurus palmatus were identified and compared. Similar to other studies, more than half of the conserved toxins are predominantly proteins including proteases. On the other hand, unique venom peptides, including ion channel toxins were revealed specifically in the M. martensii. The sodium channel toxin peptides revealed in M. martensii consolidated that scorpions in the Buthidae are able to envenomate their prey wih highly neurotoxic venom. This study suggested that these conserved proteins had already formed part of the arsenal in the venom gland of the common ancestor of scorpions, and likely perform important functional roles in envenomation during scorpion evolution.

The effect of change in mass distribution due to defensive posture on gait in fat-tailed scorpions.

In terrestrial legged locomotion, the distribution of mass can influence the gait characteristics. This can be due to a change in the magnitude or distribution of the load. The latter occurs in scorpions when they lift their large metasoma from a trailing position in ambulatory posture to the well-known arched forward position in the defensive posture. We measured how locomotion changes between these two postures by recording scorpions walking using high-speed video. We found that the metasoma in the fat-tailed scorpion (Androctonus australis) represents about a quarter of the total mass. Moving this mass anteriorly over the body changes the position of the center of mass forward 8.15 ± 1.86 mm. We found this increases the overall duty factor, and particularly that of the second leg pair, even when taking the reduced speed in defensive posture into account. In the five scorpions we recorded, also the ipsilateral phase of leg pairs 3 and 4 differed in defensive posture. We found that the trajectory the 4th foot describes during a single stride also differed significantly between postures, showing this to be a sensitive measure of changes in gait. The change from an ambulatory to a defensive posture places different demands on the gait of scorpions, possibly largely due to the forward displacement of the center of mass.

Contrasting patterns at interspecific and intraspecific levels in scorpion body size across a climatic gradient from rainforest to dryland vegetation.

Body size is believed to be one of the most fundamental functional traits in animals and is evolutionarily conserved in order to guarantee the survival of the species. Besides the phylogenetic backgrounds, body size patterns might be a product of environmental filters, especially within fine taxonomic levels (i.e., within species or geographical lineages). Here, we evaluated the responses of scorpion body size at different organizational levels (inter and intraspecific) along a dry-wet climatic gradient in Brazilian forests. Scorpions were collected from 20 localities in northeastern Brazil, covering 12 sites of dry forests and eight sites in rainforest environments. As a proxy for body size, we measured the carapace length of 368 adult scorpions belonging to 11 species and applied linear mixed-effects models to investigate the potential effects of climatic features and geographical tendencies in this trait at inter- and intraspecific levels. Our findings suggest the existence of a longitudinal pattern of body size in scorpions with species becoming larger in an east-west direction (i.e., towards the continent); such geographical tendency was also detected for one of the three species analyzed at the population level. In addition, the warmer temperature had a negative effect on body size in scorpions at inter- and intraspecific levels. Based on these findings, we assert that body size in scorpions is not affected solely by their phylogenetic history, but also by the physiological constraints imposed by the environment, which becomes more evident across climatic gradients.

Comparative morphology of scorpion metasomata: Muscles and cuticle.

Scorpions are among the most popular research objects within Arachnida and there is an impressive body of knowledge about their biology, distribution, morphology, etc. Although the poison sting has gained a lot of attention due to its potential lethal effects to humans, hitherto, there has been no comparative morphological study on the metasoma, the body part that delivers the poisonous injection. The metasoma always consists of five body segments terminated by a poison sting, but it presents significant morphological variations, both between sexes and between species. Its form ranges from long and thin to short and rather reduced to thick and dominant. In this study, we investigated species representing major scorpion clades and most of the known morphological disparity. Using high-resolution micro-computer-tomography and 3D-reconstruction, we present the first 3D visualizations of metasomal exo-skeletal elements in combination with their musculature. Despite of morphological varying metasomal forms, in all investigated species, a repeating pattern of muscles was found: four pairs of muscles in metasomal segment one to four and two pairs of muscles in metasomal segment five. However, the metasomal muscles are characterized by an antero-posterior change in their shapes and sizes and interspecific variation was also found in the extrinsic metasomal musculature, i.e. the muscles that link metasoma to mesosoma.

The central nervous system of whip spiders (Amblypygi): Large mushroom bodies receive olfactory and visual input.

Whip spiders (Amblypygi) are known for their nocturnal navigational abilities, which rely on chemosensory and tactile cues and, to a lesser degree, on vision. Unlike true spiders, the first pair of legs in whip spiders is modified into extraordinarily long sensory organs (antenniform legs) covered with thousands of mechanosensory, olfactory, and gustatory sensilla. Olfactory neurons send their axons through the leg nerve into the corresponding neuromere of the central nervous system, where they terminate on a particularly large number (about 460) of primary olfactory glomeruli, suggesting an advanced sense of smell. From the primary glomeruli, olfactory projection neurons ascend to the brain and terminate in the mushroom body calyx on a set of secondary olfactory glomeruli, a feature that is not known from olfactory pathways of other animals. Another part of the calyx receives visual input from the secondary visual neuropil (the medulla). This calyx region is composed of much smaller glomeruli ("microglomeruli"). The bimodal input and the exceptional size of their mushroom bodies may support the navigational capabilities of whip spiders. In addition to input to the mushroom body, we describe other general anatomical features of the whip spiders' central nervous system.

Structure of the pecten neuropil pathway and its innervation by bimodal peg afferents in two scorpion species.

The pectines of scorpions are comb-like structures, located ventrally behind the fourth walking legs and consisting of variable numbers of teeth, or pegs, which contain thousands of bimodal peg sensillae. The associated neuropils are situated ventrally in the synganglion, extending between the second and fourth walking leg neuromeres. While the general morphology is consistent among scorpions, taxon-specific differences in pecten and neuropil structure remain elusive but are crucial for a better understanding of chemosensory processing. We analysed two scorpion species (Mesobuthus eupeus and Heterometrus petersii) regarding their pecten neuropil anatomy and the respective peg afferent innervation with anterograde and lipophilic tracing experiments, combined with immunohistochemistry and confocal laser-scanning microscopy. The pecten neuropils consisted of three subcompartments: a posterior pecten neuropil, an anterior pecten neuropil and a hitherto unknown accessory pecten neuropil. These subregions exhibited taxon-specific variations with regard to compartmentalisation and structure. Most notable were structural differences in the anterior pecten neuropils that ranged from ovoid shape and strong fragmentation in Heterometrus petersii to elongated shape with little compartmentalisation in Mesobuthus eupeus. Labelling the afferents of distinct pegs revealed a topographic organisation of the bimodal projections along a medio-lateral axis. At the same time, all subregions along the posterior-anterior axis were innervated by a single peg's afferents. The somatotopic projection pattern of bimodal sensillae appears to be common among arachnids, including scorpions. This includes the structure and organisation of the respective neuropils and the somatotopic projection patterns of chemosensory afferents. Nonetheless, the scorpion pecten pathway exhibits unique features, e.g. glomerular compartmentalisation superimposed on somatotopy, that are assumed to allow high resolution of substrate-borne chemical gradients.

Phylogenetic and Morphological Analyses of Androctonus crassicuda from Khuzestan Province, Iran (Scorpiones: Buthidae).

The Androctonus crassicuda is the most diverse scorpion species in the family of Buthidae, which is endemic to Khuzestan province, Iran. Investigation of the relationship of species by means of a molecular study of specimens is one of the new approaches due to the limitations of the morphological approaches. In the current study, the analysis was based on 32 morphological characteristics of A. crassicuda native to southwest Iran. Moreover, the DNA sequencing of two mitochondrial markers, namely cytochrome oxidase subunit I and 12sRNA loci was performed, and the phylogenetic tree was constructed using maximum likelihood method with 1000 replications using MEGA software (version 7). Based on the results of the phylogenetic tree, A. crassicuda was classified into a monophyletic group. However, the genetic diversity of this species populations was not significant (0.001). The highest and lowest genetic distance of A. crassicuda was compared with the reports obtained in Urmia and west Azerbaijan, Iran. There was a clear divergence between the A. crassicuda isolated from northern and southern areas of Iran. This study showed the importance of geographical and climate features of the region and genetic distance among the populations. The phylogenetic analysis of Androctonus species from other regions showed the highest and lowest genetic distance with A. gonneti (Morocco) and A. amoreuxi (Portugal), respectively. The comparison of the morphological characteristics and morphometric results revealed that metasoma characteristics are important in the identification of A. crassicuda. The results of the analysis of the morphometric values of A. crassicuda were mainly compatible with the phylogenetic trees and supported the traditional morphological classification, thereby presenting a clearly definition of the genera of Androctonus species.

Air Breathing in an Exceptionally Preserved 340-Million-Year-Old Sea Scorpion.

Arachnids are the second most successful terrestrial animal group after insects [1] and were one of the first arthropod clades to successfully invade land [2]. Fossil evidence for this transition is limited, with the majority of arachnid clades first appearing in the terrestrial fossil record. Furthermore, molecular clock dating has suggested a Cambrian-Ordovician terrestrialization event for arachnids [3], some 60 Ma before their first fossils in the Silurian, although these estimates assume that arachnids evolved from a fully aquatic ancestor. Eurypterids, the sister clade to terrestrial arachnids [4-6], are known to have undergone major macroecological shifts in transitioning from marine to freshwater environments during the Devonian [7, 8]. Discoveries of apparently subaerial eurypterid trackways [9, 10] have led to the suggestion that eurypterids were even able to venture on land and possibly breathe air [11]. However, modern horseshoe crabs undertake amphibious excursions onto land to reproduce [12], rendering trace fossil evidence alone inconclusive. Here, we present details of the respiratory organs of Adelophthalmus pyrrhae sp. nov. from the Carboniferous of Montagne Noire, France [13], revealed through micro computed tomography (µ-CT) imaging. Pillar-like trabeculae on the dorsal surface of each gill lamella indicate eurypterids were capable of subaerial breathing, suggesting that book gills are the direct precursors to book lungs while vascular ancillary respiratory structures known as Kiemenplatten represent novel air-breathing structures. The discovery of air-breathing structures in eurypterids indicates that characters permitting terrestrialization accrued in the arachnid stem lineage and suggests the Cambrian-Ordovician ancestor of arachnids would also have been semi-terrestrial.

The morphology of mating plugs and its formation in scorpions: Implications for intersexual participation.

Mating plugs have been proposed as a mechanism that has evolved to avoid sperm competition. Their structure and composition vary across taxa and are related to the effectiveness of its function. This effectiveness could be related to different evolutionary interests of the sexes. Urophonius brachycentrus and Urophonius achalensis (Scorpiones, Bothriuridae) are highly suitable species to study mating plugs because both are monandrous species with specific morphological and physiological responses in the female's genitalia. Here, we analyze (a) the morphology and fine structure of the mating plugs of both species, (b) the site of production in males and the formation process of the mating plug, and (c) the changes that it undergoes over time in the female's reproductive tract. In both species, a complex mating plug obliterates the female's genital aperture and fills the genital atrium. We observed considerable interspecific variation in the mating plug morphology. A mating hemi-plug was found surrounding the capsular lobes of the hemispermatophore, which could have a mixed composition (involving portions of the hemispermatophore and glandular products). The glandular portion was transferred in a semi-solid state filling the female's genital atrium and then hardening. Changes that the plug undergoes in the female's genitalia (darkening and increase of the "distal" area of the plug) indicate a participation of the female to the formation of this type of plug. Our study provides new insights into the plugging phenomenon in scorpions, and we discussed the adaptive significance as a post-copulatory mechanism to avoid sperm competition.

Mouthpart homologies and life habits of Mesozoic long-proboscid scorpionflies.

Mesozoic long-proboscid scorpionflies (Mesopsychoidea) provide important clues to ancient plant-pollinator interactions. Among them, the family Aneuretopsychidae is especially important because its mouthparts are vital to deciphering the early evolution of Mesopsychoidea and putatively the origin of fleas (Siphonaptera). However, the identification of mouthpart homologs among Aneuretopsychidae remains controversial because of the lack of three-dimensional anatomical data. Here, we report the first Aneuretopsychidae from Late Cretaceous Burmese amber, which have short maxillary palpi and elongate mouthpart elements consisting of one pair of galeae and one hypopharynx. Their mouthparts are identical to those of Pseudopolycentropodidae (= Dualulidae, new synonym) but are not homologous to those of Siphonaptera. Our phylogenetic analysis provides robust evidence for the debated monophyly of Mesopsychoidea. Our results suggest that the long-proboscid condition has most likely evolved once in Mesopsychoidea, independently from fleas, and further reveal the variety and complexity of mid-Cretaceous pollinating insects.

A Silurian ancestral scorpion with fossilised internal anatomy illustrating a pathway to arachnid terrestrialisation.

Scorpions are among the first animals to have become fully terrestrialised. Their early fossil record is limited, and fundamental questions, including how and when they adapted to life on land, have been difficult to answer. Here we describe a new exceptionally preserved fossil scorpion from the Waukesha Biota (early Silurian, ca. 437.5-436.5 Ma) of Wisconsin, USA. This is the earliest scorpion yet reported, and it shows a combination of primitive marine chelicerate and derived arachnid characteristics. Elements of the circulatory, respiratory, and digestive systems are preserved, and they are essentially indistinguishable from those of present-day scorpions but share similarities with marine relatives. At this early point in arachnid evolution, physiological changes concomitant with the marine-to-terrestrial transition must have occurred but, remarkably, structural change in the circulatory or respiratory systems appear negligible. Whereas there is no unambiguous evidence that this early scorpion was terrestrial, this evidence suggests that ancestral scorpions were likely capable of forays onto land, a behavior similar to that of extant horseshoe crabs.

Nested helicoids in biological microstructures.

Helicoidal formations often appear in natural microstructures such as bones and arthropods exoskeletons. Named Bouligands after their discoverer, these structures are angle-ply laminates that assemble from laminae of chitin or collagen fibers embedded in a proteinaceous matrix. High resolution electron microscope images of cross-sections through scorpion claws are presented here, uncovering structural features that are different than so-far assumed. These include in-plane twisting of laminae around their corners rather than through their centers, and a second orthogonal rotation angle which gradually tilts the laminae out-of-plane. The resulting Bouligand laminate unit (BLU) is highly warped, such that neighboring BLUs are intricately intertwined, tightly nested and mechanically interlocked. Using classical laminate analysis extended to laminae tilting, it is shown that tilting significantly enhances the laminate flexural stiffness and strength, and may improve toughness by diverting crack propagation. These observations may be extended to diverse biological species and potentially applied to synthetic structures.

A new species of Centruroides (Scorpiones, Buthidae) from Colima, Mexico.

As part of an ongoing survey of scorpion diversity in Colima, Mexico, the isolated mountain Cerro Grande, part of the Biosphere Reserve Sierra de Manantlán, was investigated. Centruroides possanii sp. nov., the fifth species of the genus from the state, was discovered during fieldwork in the massif and is described in the present paper. Physiographical and climatic features of Cerro Grande may restrict the range of this new species; thus, we hypothesized that it may be a microendemic species that requires priority conservation. The new species is not assigned to any Centruroides species group recognized because some of its morphological features do not fit the current diagnosis of any of these groups, and these different groups are non-monophyletic and consequently ill-diagnosed. The new species is profusely illustrated, particularly the hemispermatophore. A distribution map is presented along with the other two more common species distributed in Colima. Because only indirect data on the potency of its venom is available, the medical importance of this new species described here is yet to be known.