A new species of Pycnothelidae Chamberlin, 1917 from the Pampean mountain ranges, Córdoba, Argentina is described and illustrated: Acanthogonatus monicae sp. nov. Here, we combine morphological analyses, molecular phylogeny based on the COI gene, species delimitation methods (bPTP, ABGD), and ecological niche modeling. These approaches consistently support two independent evolutionary lineages previously assigned to A. centralis Goloboff, 1995. The new species is morphologically similar to A. centralis and A. parana Goloboff, 1995, but differs from both by genitalic characters in males and females. Additionally, an updated identification key for Argentine species of Acanthogonatus is provided.

Understanding thermal responses in ectotherms is key to assessing vulnerability to climate change. Tarantulas (Theraphosidae) are informative models due to their sedentary lifestyle, long life cycles, and reliance on specific microhabitats. We present the first integrative assessment of the thermal ecology of Plesiopelma longisternale, a widespread Argentine species, combining experimentally derived thermal limits and thermal preferences with species distribution models, and compare its thermal profile with the sympatric Grammostola vachoni to explore patterns of thermal niche differentiation. Plesiopelma longisternale showed a minimum thermal limit near 4 °C, a maximum near 44 °C, a thermal optimum of 29.5 °C, a narrow thermal performance breadth, and a preferred temperature of approximately 32 °C. Models integrating climatic and thermal parameters predicted strong reductions in climatically suitable habitat under future warming scenarios, exceeding 70

We propose establishing a new genus of mygalomorph spiders in the family Theraphosidae Thorell, 1869, from the Province Calca, Department of Cusco, Peru. The monotypic genus Allpamayu n. gen. with its type species Allpamayu suyuwixsa n. gen, n. sp. is described. Allpamayu n. gen. differs from the known Ischnocolinae Simon, 1892 by the following unique combination of characters: abdomen with stripes, labium with a low number of cuspules, and clavate trichobothria on tarsi forming two parallel rows along half of tarsus length. Additional characters are palpal bulb of males with two keels, metatarsal ventral tumescence on the first pair of legs, cymbium with long erected setae, spermathecae of females with large subquadrate receptacles and a short wide duct oriented laterally and pointing upwards carrying two to three rounded lobes.

Sexual selection is a pervasive evolutionary force shaping the extraordinary diversity of animal genitalia, often driving rapid morphological divergence and complex interactions between male and female reproductive structures. In spiders, sexual selection acts through both pre- and postcopulatory mechanisms, frequently resulting in elaborate male intromittent organs, specialized female sperm-storage structures, and intricate mating behaviours. Despite this diversity, mygalomorph spiders have traditionally been regarded as morphologically conservative, with comparatively simple genitalia and stereotyped reproductive patterns. In this study, we provide the first integrative analysis of genital functional morphology, copulatory mechanics, and mating behaviour in a mygalomorph species, Mecicobothrium thorelli. Our results reveal a surprising degree of anatomical and behavioural complexity. Most notably, we document the first known instance of directional genital asymmetry in a mygalomorph spider. Female genitalia are characterized by two distinct spermathecal types, with one being asymmetric. This asymmetry is matched behaviourally by differential, selective use of the symmetric male copulatory organs. The consistent preference for specific male-female genitalia combinations suggests finely tuned mechanical and functional coordination during copulation. By uncovering these hidden complexities, our study expands current understanding of sexual selection and genital evolution in early-diverging spider lineages.

Actinopus comprises 98 species of trapdoor spiders endemic to the Neotropic region. In southwestern Buenos Aires, Argentina, four species are recorded: Actinopus casuhati Rios-Tamayo and Goloboff, 2018, A. laventana Miglio, Perez-Miles & Bonaldo, 2020, Actinopus patagonia Rios-Tamayo and Goloboff, 2018, and Actinopus puelche Rios-Tamayo and Goloboff, 2018; females of A. puelche are unknown. By the examination of Actinopus from Bahia Blanca district, southwestern Buenos Aires province, we found specimens that do not fit within any of the known species. Thus, we implemented an integrative approach combining molecular and morphological evidence to describe, diagnose and illustrate Actinopus obrerografico sp. nov. In addition, we describe for the first time the female of A. puelche. We also present new distributional records for A. patagonia and A. puelche. Males of A. obrerografico sp. nov. Can be distinguished by having red tarsi and metatarsi, and bulb with well developed keels and apophysis, and no denticles along the inferior prolateral keel; females, can be distinguished by the spermathecae, bilobed with external lobe well developed and an internal basal proejection. Females of A. puelche can be distinguished by having a spermathecae with slight marked lobes. A first molecular phylogeny using Maximum likelihood yielded Actinopus as monophyletic, A. obrerografico sp. nov. as a distinct clade and A. puelche more related to the remaining Argentinean species despite living in sympatry with A. obrerografico sp. nov.

The present study contributes to the understanding of the diversity within the tarantula genus Euathlus Ausserer, 1875. Through a combination of cladistic, molecular, and morphological analyses, three new species are described: Euathlus basalticus sp. nov. from Neuquén, Euathlus kupal sp. nov. from Mendoza, and Euathlus susanae sp. nov. from the La Pampa-Mendoza provinces. Additionally, the female of Euathlus tenebrarum Ferretti, 2015 is described for the first time, revealing that the previously attributed female of this species belongs to E. basalticus sp. nov. Phylogenetic trees from both morphological and molecular datasets are presented. Preliminary molecular analyses reveal the identity and support the proposal of the species treated here. Morphological analyses found considerable diversity within Euathlus, particularly in genitalic structures, challenging the general assumption of morphological homogeneity among mygalomorph spiders. Cladistic analyses recovered the genus Phrixotrichus within Euathlus, though this hypothesis could not be tested with molecular data due to the lack of available sequences for Phrixotrichus. These results suggest that future taxonomic revisions may be complemented once molecular data become available. Altogether, our results provide new insights into the systematics and diversity of Euathlus and highlight the importance of integrative approaches for unraveling evolutionary relationships within this group.

ABSTRACT The family Pycnothelidae comprises medium to small-sized spiders that construct silk tubes under stones or logs or dig burrows in open environments. In Argentina, Acanthogonatus centralis Goloboff, 1995 and Stenoterommata platensis Holmberg, 1881 are two species commonly found in central region, associated to the mountainous grasslands or to the La Plata River Basin. The Tandilia mountainous grassland is an extended belt located southeastern Buenos Aires province, Argentina. Although some pycnothelid spiders are distributed close to this mountainous system, they are not recorded in Tandilia. Through niche modeling we attempt to evaluate the influence of bioclimatic variables in shaping the distribution of these species and explore their absence in the mountainous belt under past, present and future climatic conditions. We found that Tandilia is a non-suitable area for the establishment of the populations of these species with the exception of Stenoterommata platensis under a future scenario of climatic change.

This work aims to describe a new species of Thrixopelma Schmidt, 1994 from southcentral Peru in the Department of Cusco. Thrixopelma choquequirao sp. nov. can be easily distinguished from congeneric species by the low number of labial cuspules, a very long palpal tibia, morphology of the male palpal bulb and female spermathecae. Currently the genus Thrixopelma comprises seven formally described species which inhabit Peru and Ecuador, distributed in Amazonian rainforest, Coastal Dry Forest, and Andean Dry Forest.

A new species of Chaco Tullgren, 1905 was discovered and is formally described. Chaco aoni sp. nov. from the Santa Cruz River in Santa Cruz Province, Argentina, is the southernmost recorded species of this genus. The new species is diagnosed on the basis of the morphology of the palpal organ and tibial apophysis of males and the shape of the spermathecae of females. A cladistic analysis was carried out based on an already published morphological matrix, which now also includes the new species. This new species is part of a monophyletic group including also Chaco tingua Indicatti, Goloboff, 1995 and C. ansilta Ferretti, 2014.

Plesiopelma longisternale is a widespread tarantula in Argentina and its limit is difficult to determine due to their morphological variation among populations. Males are distinguishable by the following character combination: a field of spines on the apical half of the palpal tibia, a very long embolus and a field of spines on the reotrolateral face of cymbium; females are characterized by long spiraled ducts distant from each other. Here, we used mitochondrial DNA (cox1) to reconstruct the first phylogeny of P. longisternale, in combination with morphological data and molecular species delimitation, to assess the taxonomic limits of this species. Our phylogenetic results confirm a close relationship among the populations from central Argentina and a new evolutionary independent lineage identified as a new species, Plesiopelma absconditus, which is here diagnose, described and illustrated. We further analyzed the diagnostic characters of P. longisternale through the examination of the types and specimens from many populations and found that their morphological intraspecific variations largely overlap. Altogether, our results demonstrate that some of the variability of P. longisternale in central Argentina represent polymorphisms of a single species supported by molecular data. In addition, we discovered a new species from this genus distinguishable by molecular and morphological data and highlight the need for multiple lines of evidence to solve the taxonomic problems in species of tarantulas.

Environmental characteristics act as limiting factors for the establishment and survival of organisms, and this holds particular significance for ectothermic. Grammostola vachoni is an endemic Argentinean tarantula that inhabits central mountainous grasslands. In this study, we model their potential distribution and assess thermal parameters and vulnerability indices in unstudied populations to understand the species’ survival limits. The models to explain the geographic distribution of G. vachoni demonstrate a non-random pattern and robust predictive capabilities. The monthly variables in December, October, and March were the greatest influence. Respect to thermal parameters calculated throughout locomotor performance, the critical thermal limits were 4.9 °C and 51.1 °C, and the preferred temperatures were correlated whit optimal temperature. According the occurrence probability, the species has a low probability of persisting in extreme coldest and hottest environments. In a more temperate environment, the probability increases, mostly at temperatures of about 35 °C. The thermal performance breadth was 19.30, the thermal tolerance range was 46.1 °C and the inferior and superior limits of B80 were 18.9 °C and 37.1 °C. Grammostola vachoni show a better performance at higher temperatures, and a preference for higher temperatures than other ectotherms. The diverse microclimates provide by the heterogeneous nature of mountain grassland outcrops can act as a refuge. Implications for insect conservation: Our results show that grassland outcrops play a key role in maintaining the G. vachoni population, as these environments appear to be less affected in the future. Moreover, the species’ locomotor performance could cope with future thermal shifts.

Two new species of Euathlus (Verhandlungen der Kaiserlich-K & ouml;niglichen Zoologisch-Botanischen Gesellschaft in Wien, 1875, 25, 125) from Argentina are described. Euathlus ameghinoi sp. n. and Euathlus ventus sp. n. are the first records for the Patagonian Steppe. Here we used mitochondrial DNA (cox1) to perform the first molecular phylogeny of some representatives of the genus. In addition, we present the first description of the sexual behaviour of the genus. Both molecular and cladistic morphological analysis showed the genus Euathlus as monophyletic, and new species were recovered as sister groups. New species show new morphological variations of typical characters for the genus (e.g. tibial apophyses and palpal organs).

In this contribution, Heterothele caudicula Simon, 1886 (Theraphosidae) is transferred to the genus Thalerommata Ausserer, 1875. Thalerommata caudicula new combination is based on the examination of the type that is characterized by flattened iridescent setae covering the abdomen, a synapomorphy of this genus. Thus, this is the ninth species of the genus known and Heterothele caudicula is removed from the Argentinean theraphosid fauna.

The loss of biodiversity due to the effects of a number of human activities is a cause for great concern. Protected areas are currently one of the main conservation tools worldwide and their correct selection and design play a key role. Since 2000, there have been protocols for systematic conservation planning, which emphasize the identification of priority conservation areas (PCAs) to ensure the persistence of species habitats and the environmental processes associated with them. Spiders of the family Theraphosidae (tarantulas) have biological characteristics that make them vulnerable to fragmentation in time and space and also are underrepresented in current conservation efforts. The geographical distribution of endemic species, such as tarantulas, represents a historical and ecological footprint of all biological entities; therefore, such endemic areas are recognized as priority areas for biodiversity conservation plans. The present work aims to develop an integrative biogeographical approach to conservation through the evaluation of multispecies distribution patterns, and the study of species richness and areas of endemism of tarantulas in Argentina with the ultimate goal of assessing their relationship to existing protected areas and proposing PCAs.

Trapdoor spiders are known for digging deep burrows into the ground closed with a thick trapdoor. Actinopus balcarce Ríos-Tamayo & Goloboff was described based on two males from Balcarce, Buenos Aires, Argentina. In a recent survey in the type locality, we found females probably belonging to this species. Morphology of the females found allowed us to attribute them to Actinopus balcarce, which are described for the first time. Photographs of the spermathecae are presented along with comments on the natural history of the species. Some morphological insights on the female of this species are also discussed.

Thermal preference and thermal performance are used to describe the thermal biology of an ectothermic organism through parameters, i.e., estimating locomotor performance by maximum running speed. In this study, we assessed the thermal preference and locomotor performance of the spider Mecicobothrium thorelli Holmberg, 1882, a wintry mygalomorph spider endemic to the native mountainous grasslands of central Argentina and Uruguay. The preferred temperatures of the 72.4% of the individuals were in the range of 10–20 °C. The highest frequencies of preferred temperatures were 10–15 °C in males and 15–20 °C in females. The sprint speed showed significant differences between all the temperatures evaluated and showed the highest speeds at 25 °C and the lowest at 3 °C. The optimal temperature was 26.09 °C, which was significantly higher than the preferred temperature in both males and females. We concluded that M. thorelli selects a wide range of temperatures and prefers to stay in medium and low temperatures, which are correlated with winter activity in the wild. However, the species showed maximum speed at higher temperatures, which implies that spiders would perform even better in nature and maximize their locomotion by being active during a warmer period.