Systematic Revision of the Giant Vinegaroons of theMastigoproctus giganteusComplex (Thelyphonida: Thelyphonidae) of North America

Pinheiro A, Silva TA, Lima D. Description of a new fossil Thelyphonida (Arachnida, Uropygi) and further record of Cratosolpuga wunderlichi Selden, in Selden and Shear, 1996 (Arachnida, Solifugae) from Crato Formation (Aptian/Albian), Araripe Basin, Brazil

Background

A new fossil species of whipscorpion, Mesoproctus rayoli n. sp., is described. The specimen originates from the Crato Formation, dating to the Lower Cretaceous (Aptian/Albian) period within the Araripe Sedimentary Basin. This species has been provisionally assigned to Mesoproctus Dunlop, 1998, as it represents the sole known Thelyphonida fossil genus discovered in South America and within Araripe Lagerstätte.

Methods

The material underwent detailed description and illustration processes. Key diagnostic characters, such as body length, pedipalpal coxae apophysis, the form of the opisthosoma, and the length of leg IV, were meticulously examined. SEM methods were applied in this study.

Results

Through the detailed analysis, comparisons and differences to Mesoproctus rowlandi Dunlop, 1998 were made possible. Additionally, a well-preserved specimen of the rare camel spider, Cratosolpuga wunderlichi Selden, in Selden and Shear, 1996, was identified from the limestones of the Crato Formation. The newly discovered fossil specimen of Cratosolpuga wunderlichi suggests two characters not previously described: (i) a segmented tarsomere on leg IV; and (ii) a leg I with one tarsal claw.

Sexual selection and predation drive the repeated evolution of stridulation in Heteroptera and other arthropods

Acoustic and substrate-borne vibrations are among the most widely used signalling modalities in animals. Arthropods display a staggering diversity of vibroacoustic organs generating acoustic sound and/or substrate-borne vibrations, and are fundamental to our broader understanding of the evolution of animal signalling. The primary mechanism that arthropods use to generate vibroacoustic signals is stridulation, which involves the rubbing together of opposing body parts. Although stridulation is common, its behavioural context and evolutionary drivers are often hard to pinpoint, owing to limited synthesis of empirical observations on stridulatory species. This is exacerbated by the diversity of mechanisms involved and the sparsity of their description in the literature, which renders their documentation a challenging task. Here, we present the most comprehensive review to date on the systematic distribution and behavioural context of stridulation. We use the megadiverse heteropteran insects as a model, together with multiple arthropod outgroups (arachnids, myriapods, and selected pancrustaceans). We find that stridulatory vibroacoustic signalling has evolved independently at least 84 times and is present in roughly 20% of Heteroptera, representing a remarkable case of convergent evolution. By studying the behavioural context of stridulation across Heteroptera and 189 outgroup lineages, we find that predation pressure and sexual selection are the main behaviours associated with stridulation across arthropods, adding further evidence for their role as drivers of large-scale signalling and morphological innovation in animals. Remarkably, the absence of tympanal ears in most Heteroptera suggests that they typically cannot detect the acoustic component of their stridulatory signals. This demonstrates that the adoption of new signalling modalities is not always correlated with the ability to perceive those signals, especially when these signals are directed towards interspecific receivers in defensive contexts. Furthermore, by mapping their morphology and systematic distribution, we show that stridulatory organs tend to evolve in specific body parts, likely originating from cleaning motions and pre-copulatory displays that are common to most arthropods. By synthesising our understanding of stridulation and stridulatory organs across major arthropod groups, we create the necessary framework for future studies to explore their systematic and behavioural significance, their potential role in sensory evolution and innovation, and the biomechanics of this mode of signalling.

Taxonomy of the thelyphonid genus Typopeltis Pocock, 1894, including homology proposals for the male gonopod structures (Arachnida, Thelyphonida, Typopeltinae)

The genus Typopeltis Pocock, 1894 is poorly known regarding its systematics, natural history, and distribution, despite important taxonomic advances during the 1990s. Currently, only 13 species are known from East Asia, including areas in south China, Japan, Vietnam, Laos, Thailand, and Taiwan. In this work, we describe and illustrate a new species of Typopeltis from Vietnam and provide a new description for the male of T.guangxiensis Haupt & Song, 1996. Additionally, we describe and illustrate the female gonopod of T.guangxiensis for the first time and propose a new homology hypothesis for the male gonopod parts. The male of T.laurentianus sp. n. is characterized by the unique patellar apophysis that presents a smooth texture and no spines. Typopeltislaurentianus sp. n. is the third species of this genus to be described from Vietnam.

Miniaturisation in Chelicerata

Arachnids and their relatives (Chelicerata) range in body length from tens of centimetres in horseshoe crabs down to little more than 80-200 μm in several groups of mites. Spiders (Araneae) show the widest range within a given Bauplan - the largest species being ca. 270 times longer than the smallest - making them excellent models to investigate scaling effects. The two mite clades (Parasitiformes and Acariformes) are the main specialists in being small. Miniaturisation, and its consequences, is reviewed for both fossil and extant chelicerates. Morphological changes potentially related to miniaturisation, or adapting to the ecological niches that small size allows, include reduction in the length and number of legs, loss of prosomal arteries (and eventually also the heart), replacement of book lungs by tracheae, or even loss of all respiratory organs. There may also be evolutionary novelties, such as the acquisition of structures by which some mites attach themselves to larger hosts. The observed character distributions suggest a fairly fundamental division between larger pulmonate (lung-bearing) arachnids and smaller, non-pulmonate, groups which could reflect a phylogenetic dichotomy. However, it is worth noting that lineages of tiny spiders were originally fully pulmonate, but have acquired some typically non-pulmonate features, while camel spiders (Soli-fugae) can be large but have a Bauplan suggestive of smaller, non-pulmonate, ancestors.