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Chelicerae, distinctive feeding appendages in chelicerates, such as spiders, scorpions, or horseshoe crabs, can be classified based on their orientation relative to the body axis simplified as either orthognathous (parallel) or labidognathous (inclined), exhibiting considerable diversity across various taxa. Among extinct chelicerates, sea scorpions belonging to the Pterygotidae represent the only chelicerates possessing markedly elongated chelicerae relative to body length. Despite various hypotheses regarding the potential ecological functions and feeding movements of these structures, no comprehensive 3D kinematic investigation has been conducted yet to test these ideas. In this study, we generated a comprehensive 3D model of the pterygotid Acutiramus, making the elongated right chelicera movable by equipping it with virtual joint axes for conducting Range of Motion analyses. Due to the absence in the fossil record of a clear indication of the chelicerae orientation and their potential lateral or ventral movements (vertical or horizontal insertion of joint axis 1), we explored the Range of Motion analyses under four distinct kinematic settings with two orientation modes (euthygnathous, klinogathous) analogous to the terminology of the terrestrial relatives. The most plausible kinematic setting involved euthygnathous chelicerae being folded ventrally over a horizontal joint axis. This configuration positioned the chelicera closest to the oral opening. Concerning the maximum excursion angle, our analysis revealed that the chela could open up to 70°, while it could be retracted against the basal element to a maximum of 145°. The maximum excursion in the proximal joint varied between 55° and 120° based on the insertion and orientation. Our findings underscore the utility of applying 3D kinematics to fossilized arthropods for addressing inquiries on functional ecology such as prey capture and handling, enabling insights into their possible behavioral patterns. Pterygotidae likely captured and processed their prey using the chelicerae, subsequently transporting it to the oral opening with the assistance of other prosomal appendages. How pterygotid sea scorpions used their tripartite elongate cheliceres to get prey items close to the mouth region remains a conundrum. We applied four different 3D kinematic settings with regard to insertion and orientation of the cheliceres to examine the most likely way this was realized. We found orthognathous cheliceres with a horizontal proximal joint axis allowing for a ventral movement the most logical to have been established.

Despite the diversity in fish auditory structures, it remains elusive how otolith morphology and swim bladder-inner ear (= otophysic) connections affect otolith motion and inner ear stimulation. A recent study visualized sound-induced otolith motion; but tank acoustics revealed a complex mixture of sound pressure and particle motion. To separate sound pressure and sound-induced particle motion, we constructed a transparent standing wave tube-like tank equipped with an inertial shaker at each end while using X-ray phase contrast imaging. Driving the shakers in phase resulted in maximised sound pressure at the tank centre, whereas particle motion was maximised when shakers were driven out of phase (180°). We studied the effects of two types of otophysic connections-i.e. the Weberian apparatus (Carassius auratus) and anterior swim bladder extensions contacting the inner ears (Etroplus canarensis)-on otolith motion when fish were subjected to a 200 Hz stimulus. Saccular otolith motion was more pronounced when the swim bladder walls oscillated under the maximised sound pressure condition. The otolith motion patterns mainly matched the orientation patterns of ciliary bundles on the sensory epithelia. Our setup enabled the characterization of the interplay between the auditory structures and provided first experimental evidence of how different types of otophysic connections affect otolith motion.

The last common ancestor of all living arthropods had biramous postantennal appendages, with an endopodite and exopodite branching off the limb base. Morphological evidence for homology of these rami between crustaceans and chelicerates has, however, been challenged by data from clonal composition and from knockout of leg patterning genes. Cambrian arthropod fossils have been cited as providing support for competing hypotheses about biramy but have shed little light on additional lateral outgrowths, known as exites. Here we draw on microtomographic imaging of the Cambrian great-appendage arthropod Leanchoilia to reveal a previously undetected exite at the base of most appendages, composed of overlapping lamellae. A morphologically similar, and we infer homologous, exite is documented in the same position in members of the trilobite-allied Artiopoda. This early Cambrian exite morphology supplements an emerging picture from gene expression that exites may have a deeper origin in arthropod phylogeny than has been appreciated. The common ancestor of all living arthropods had biramous postantennal appendages, with an endopodite and exopodite branching off the limb base. This study uses microtomographic imaging of the Cambrian arthropod Leanchoilia to reveal a previously undetected exite at the base of most appendages, suggesting a deeper origin for exites in arthropod phylogeny.

Background The early Cambrian arthropod clade Megacheira, also referred to as great appendage arthropods, comprised a group of diminutive and elongated predators during the early Palaeozoic era, around 518 million years ago. In addition to those identified in the mid-Cambrian Burgess Shale biota, numerous species are documented in the renowned 518-million-year-old Chengjiang biota of South China. Notably, one species, Tanglangia longicaudata , has remained inadequately understood due to limited available material and technological constraints. In this study, we, for the first time, examined eight fossil specimens (six individuals) utilizing state-of-the-art μ CT and computer-based 3D rendering techniques to unveil the hitherto hidden ventral and appendicular morphology of this species. Results We have identified a set of slender endopodites gradually narrowing distally, along with a leaf-shaped exopodite adorned with fringed setae along its margins, and a small putative exite attached to the basipodite. Our techniques have further revealed the presence of four pairs of biramous appendages in the head, aligning with the recently reported six-segmented head in other early euarthropods. Additionally, we have discerned two peduncle elements for the great appendage. These findings underscore that, despite the morphological diversity observed in early euarthropods, there exists similarity in appendicular morphology across various groups. In addition, we critically examine the existing literature on this taxon, disentangling previous mislabelings, mentions, descriptions, and, most importantly, illustrations. Conclusions The μ CT-based investigation of fossil material of Tanglangia longicaudata , a distinctive early Cambrian euarthropod from the renowned Chengjiang biota, enhances our comprehensive understanding of the evolutionary morphology of the Megacheira. Its overall morphological features, including large cup-shaped eyes, raptorial great appendages, and a remarkably elongated telson, suggest its potential ecological role as a crepuscular predator and adept swimmer in turbid waters.

Background Only a few studies have examined the visual systems of Amblypygi (whip spiders) until now. To get new insights suitable for phylogenetic analysis we studied the axonal trajectories and neuropil architecture of the visual systems of several whip spider species ( Heterophrynus elaphus , Damon medius , Phrynus pseudoparvulus , and P. marginemaculatus ) with different neuroanatomical techniques. The R-cell axon terminals were identified with Cobalt fills. To describe the morphology of the visual neuropils and of the protocerebrum generally we used Wigglesworth stains and μCT. Results The visual system of whip spiders comprises one pair of median and three pairs of lateral eyes. The R-cells of both eye types terminate each in a first and a second visual neuropil. Furthermore, a few R-cell fibres from the median eyes leave the second median eye visual neuropil and terminate in the second lateral eye neuropil. This means R-cell terminals from the lateral eyes and the median eyes overlap. Additionally, the arcuate body and the mushroom bodies are described. Conclusions A detailed comparison of our findings with previously studied chelicerate visual systems (i.e., Xiphosura, Scorpiones, Pseudoscorpiones, Opiliones, and Araneae) seem to support the idea of close evolutionary relationships between Xiphosura, Scorpiones, and Amblypygi.

This article emphasises the importance of parasitological research in understanding ecological dynamics and biodiversity conservation through a global analysis of quill mites (Syringophilidae) parasitising Sunbirds (Nectariniidae). Data from 764 Sunbird individuals across seventy-six species revealed twelve quill mite species, including three newly described species: Aulonastus aethopygus Sikora and Unsoeld sp. n., Syringophiloidus haeckeli Sikora and Unsoeld sp. n., and Aulonastus arachnotherus Sikora and Unsoeld sp. n. A bipartite network analysis indicated a low connectance of 0.10, suggesting that only 10% of potential bird–parasite connections are realised. This high specialisation is further supported by an H2′ index of 0.94 and a C score of 0.83, indicating low co-occurrence among mite species. The temperature of nestedness at 13.49 suggests a well-organised network structure. Additionally, normalised specialisation (d’) ranged from 0.60 to 1, reflecting unique host–parasite interactions. High modularity (likelihood = 0.80) with nine modules was identified, with hosts ranging from one to seven. The study concludes by discussing the host–parasite dynamics and their ecological implications within this system.

While birds-of-paradise (Passeriformes: Paradisaeidae) are a well-known group of birds, our understanding of their parasites is still limited. This study reports on parasitic quill mites of the subfamily Picobiinae (Acariformes: Syringophilidae), which have never before been recorded on this group of birds. The mite specimens presented in this paper were collected from birds-of-paradise that had been captured in Papua New Guinea and Indonesia in the years 1910–1911 and are now deposited in the Bavarian State Collection of Zoology, Munich, Germany. Two syringophilid species are described as new to science: (i) Picobia frankei sp. n. from the magnificent riflebird Lophorina magnifica, the glossy-mantled manucode Manucodia ater, and the crinkle-collared manucode Manucodia chalybatus, and (ii) Gunabopicobia garylarsoni sp. n. from the twelve-wired bird-of-paradise Seleucidis melanoleucus and the lesser bird-of-paradise Paradisaea minor. We hypothesise that the presence of both picobiine species on phylogenetically unrelated paradisaeids may be caused by the sexual behaviour of these birds, where interspecific copulations may play a role in the switching of parasites between non-closely related host species.

Mites associated with birds comprise representatives of numerous families and display a remarkable diversity of ecological strategies, ranging from commensalism, in which the mite benefits without causing measurable harm to its host, to parasitism, which can lead to direct damage through feeding on host tissues or resources [...]

More than half a billion years ago, a high diversity of organisms appeared in the fossil record. All major clades we know today already existed, and arthropods dominated the marine faunas. Many were already equipped with a pair of elaborated compound eyes on top of movable eye stalks. Some of them also possessed 3-4 small single-aperture eyes, so-called median eyes. Just trilobites possessed sessile dorsal eyes. One pair of compound eyes/lateral eyes is considered plesiomorphic and is a common trait for euarthropods. Here, we describe an arthropod that possessed two independent compound eye systems—a pair of stalked and a pair of tiny sessile dorsal trilobite-like compound eyes, unique in the arthropod kingdom so far. A competition between prey and predators for the capacity of vision triggered the evolution of visual systems, and we discuss this newly described system(s) in its evolutionary context and ecological significance. Regarding its eye system phylogenetically, P. daziensis reinforces the position of a now non-missing link between the non-trilobite artiopodans and trilobites. Arthropods typically possess two eye systems—one pair of compound eyes and ocellar median eyes. Pygmaclypeatus daziensis , a Lower Cambrian arthropod, is equipped with two pairs of different compound eyes—ventrally stalked, movable compound eyes and dorsally, trilobite-like sessile ones.

Quill mites of the family Syringophilidae (Acariformes: Prostigmata) are highly specialised avian ectoparasites that inhabit feather quills. Despite their widespread occurrence, their diversity, distribution, and host associations remain poorly understood. This study examined the diversity and ecological interactions of syringophilid mites parasitising Euphoninae hosts. We analysed 298 dry bird skins representing 25 species deposited in the Bavarian State Collection for Zoology in Munich, Germany. Quill mite infestations were detected in 15 host species, identifying 4 mite species, including 2 newly described taxa: Aulonastus neotropicalis sp. n. and Syringophilopsis euphonicus sp. n. Infestation prevalence ranged from 2% to 25%. Quill mite–host interactions exhibited high specialisation and niche differentiation, with no co-occurring species sharing the same microhabitat. Network analysis indicated moderate connectance (0.35) and significant host specificity (H2′ = 0.77, p = 0.007). Biogeographic history suggests that divergence from Carduelinae and subsequent evolutionary events shaped syringophilid diversity in Euphoninae. These findings underscore the importance of museum collections in uncovering cryptic parasite diversity and provide new insights into host–parasite co-evolutionary dynamics.