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The fine structure of the book lungs in 29 species representing ten monophyletic taxa of the Scorpiones (Arachnida) was investigated using scanning electron microscopy (SEM). Scorpion lungs are not homogeneous across the group. Here we describe and score three sets of phylogenetically informative characters: (1) the surface ornament of the lung lamellae, (2) the distal margins of the lamellae and (3) the fine structure of the spiracle margin. Provisional results suggest that reticulation on the surface of the lung lamellae is characteristic of the Buthidae. By contrast, non-buthid scorpions maintain the air space between adjacent lamellae using projecting trabeculae. Typically they are simple struts, but the trabeculae are distally branched in all investigated Scorpionidae, plus at least one species belonging to the Liochelidae. Simple thorns on the lamellar margins probably represent the plesiomorphic condition, while more complex, branched, arcuate morphologies appear to be homoplastic, occurring sporadically in numerous scorpion sub-groups. The tightly packed, hexagonal pillars around the posterior margin of the spiracle support a close relationship between Scorpionidae and Liochelidae, to the exclusion of the Urodacidae.

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The book lungs of an exceptionally preserved fossil arachnid (Trigonotarbida) from the Early Devonian (approx. 410 Myr ago) Rhynie cherts of Scotland were studied using a non-destructive imaging technique. Our three-dimensional modelling of fine structures, based on assembling successive images made at different focal planes through the translucent chert matrix, revealed for the first time fossil trabeculae: tiny cuticular pillars separating adjacent lung lamellae and creating a permanent air space. Trabeculae thus show unequivocally that trigonotarbids were fully terrestrial and that the microanatomy of the earliest known lungs is indistinguishable from that in modern Arachnida. A recurrent controversy in arachnid evolution is whether the similarity between the book lungs of Pantetrapulmonata (i.e. spiders, trigonotarbids, etc.) and those of scorpions is a result of convergence. Drawing on comparative studies of extant taxa, we have identified explicit characters (trabeculae, spines on the lamellar edge) shared by living and fossil arachnid respiratory organs, which support the hypothesis that book lungs were derived from a single, common, presumably terrestrial, ancestor.

A fossil trigonotarbid (Arachnida: Trigonotarbida) assigned to Palaeocharinus sp. from the Early Devonian (c. 410 Ma) Rhynie cherts of Aberdeenshire, Scotland, UK is described, speciWcally for a previously unrecognised feature of the distal end of the pedipalp. This exhibits a small chela formed from a movable, unpaired apotele articulating against a slightly shorter, Wxed projection from the inferior surface of the tarsus. Among other arachnids, this morphology has only previously been observed in the rare and enigmatic Carboniferous-Recent taxon Ricinulei. This character oVers explicit support for a monophylum (Trigonotarbida + Ricinulei); a hypothesis previously based on opisthosomal characters which (if correct) would draw Ricinulei within the so-called Pantetrapulmonata clade (i.e. spiders and their closest relatives). Our data is not consistent with Ricinulei's traditional position as sister-group of mites (Acari) and is an example of how considering extinct taxa may help to resolve the position of a 'diYcult' living group.

wl-N 8 fiGUFES AND 1 "IABIE POSCHMANN, M.; DUNLOP, J.A.; KAMENZ, C. & SCHOLTZ, G. 2008. The Lower Devonian scorpion Waeringoscorpio and the respiratory nature of its filamentous structures, with the description of a new species from the Westerwald area, Germany. -Pal~iontologische Zeitschrift 82 (4): 418-436, 8 figs., 1 tab., Stuttgart, 31.12. 2008. Abstract:The fossil scorpion Waeringoscorpio hefteri STORMER, 1970 (Arachnida: Scorpiones) from the Lower Devonian of the Rhenish Massif of Germany is redescribed based on both the original type and newly collected material. A second, more tuberculate species from Siegenian strata near BiJrdenbach in the Westerwald (also part of the Rhenish Massif) is described as W. westerwaldensis n. sp. Details of the coxo-stemal region -including the lack of an oral tube -and the number of ventral mesosomal plates are discussed. Waeringoscorpio STORMER, 1970 is I~est known for its possession of extemally-projecting 'gills'. Our new material reveals that these are indeed pair-wise bundles of rigid, branching filaments which originate laterally, quite possibly from those segments of the mesosoma associated with the book lungs in extant scorpions. Their gross morphology is most consistent with a respiratory organ adapted for use in water. Indeed their closest modem analogues are the tracheal gills of secondarily aquatic insects. We suggest that the morphology and likely palaeoenvironment of Waeringoscorpio could indicate an aquatic animal, but we draw attention to the uniqueness of its gill-structures, which may not be part of the scorpion groundpattern. Thus, Waeringoscorpio was perhaps a secondarily aquatic scorpion adapted for benthic life in oxygenstressed, freshwater-brackish environments.Kurzfassung: Der fossile Skorpion Waeringoscorpio hefieri STORMER, 1970 (Arachnida: Scorpiones) aus dem Unterdevon (Emsium) des Rheinischen Schiefergebirges wird anhand des Typusmaterials und weiterer Funde neu beschrieben. Eine zweite, st~irker tuberkulierte Art aus dem Siegenium von Btirdenbach im Westerwald wird als W. westerwaldensis n. sp. beschrieben. Details der Coxo-Stemal-Region -ein Mundvorraum ist nicht ausgebildet -und die Anzahl der ventralen, mesosomalen Platten werden diskutiert. Waeringoscorpio STORMER, 1970 ist aufgrund der Ausbildung seitlich abstehender, mrglicherweise schlauchartiger Filamente am Mesosoma und ihrer mrglichen Funktion als ,,Kiemen" yon besonderem Interesse. Unser neues Material zeigt, dass es sich bei diesen Strukturen um paarige Btindel steifer, sich distad verzweigender Rrhren handelt, die seitlich der mesosomalen Segmente entspringen, welche bei rezenten Skorpionen die Buchhmgen tragen. Ihre ~iuBere Anatomie l~isst sich am ehesten mit einer Funktion als Atmungsorgan, angepasst an ein aquatisches Milieu, in Einklang bringen. Eine bemerkenswert grol3e morphologische Ubereinstimmung zeigen die Tracheenkiemen einiger Larven heutiger, sekund/~r aquatischer Insekten. Morphologie und der wahrscheinliche Lebensraum von Waeringoscorpio weisen auf ein wasserlebende...

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Invasion of the land by arachnids required adaptations of numerous organs, such as gills evolving into lungs, as well as mechanisms facilitating sperm transfer in a terrestrial environment. Many modern arachnids use spermatophores for this purpose, i.e. sperm transmitters detached from the body. Exceptionally preserved Silurian (423 Ma) fossils of Eurypterus tetragonophthalmus Fischer, 1839 (Chelicerata: Eurypterida) preserve so-called 'horn organs' which we here demonstrate as being equivalent to the spermatophore-producing parts of the genital tract in certain modern arachnids. This clarifies a long-running debate about sexing eurypterids based on the shape of the median abdominal (or genital) appendage. To our knowledge this is also the oldest direct evidence for spermatophore-mediated sperm transfer in the fossil record and suggests that eurypterids had evolved mating techniques using spermatophores as early as the Silurian, a valuable prerequisite for life on land. Spermatophores are absent in sea spiders (Pycnogonida) and horseshoe crabs (Xiphosura); thus the shared presence of sclerotized sperm-transfer devices in eurypterids and arachnids is a novel character, newly elucidated here, which offers explicit support for (Eurypterida + Arachnida). For this clade the name Sclerophorata n. nov. is proposed. Arachnida can be further defined by fusion of the originally paired genital opening.