Arthropod

Xiphosurids are an archaic group of aquatic chelicerate arthropods, generally known by the colloquial misnomer of ‘horseshoe crabs’. Known from marine envi- ronments as far back as the early Ordovician, horseshoe crabs are generally considered ‘living fossils’ – descendants of a bradytelic lineage exhibiting little morphological or ecological variation throughout geological time. However, xiphosurids are known from freshwater sediments in the Palaeozoic and Mesozoic; furthermore, the contention that xiphosurids show little morphological variation has never been tested empirically. Attempts to test this are hampered by the lack of a modern phylogenetic framework with which to explore different evolutionary scenarios. Here, I present a phylogenetic analysis of Xiphosurida and explore patterns of morphospace and environmental occupation of the group throughout the Phanerozoic. Xiphosurids are shown to have invaded non-marine environments indepen- dently at least five times throughout their evolutionary history, twice resulting in the radiation of major clades – bellinurines and austrolimulids – that occupied novel regions of morphospace. These clades show a convergent ecological pattern of differentiation, speciation and subse- quent extinction. Horseshoe crabs are shown to have a more dynamic and complex evolutionary history than previ- ously supposed, with the extant species representing only a fraction of the group’s past ecological and morphological diversity.

The order Decapoda represents a species-rich group of crustaceans. Numerous economically important and morphologically diverse members of this group have been studied extensively for many decades, in part to understand their phylogeny. There are several competing hypotheses concerning relationships among the major lineages of Decapoda. Our laboratories are estimating a robust decapod phylogeny based on molecular and morphological data in an attempt to resolve relationships among major lineages. The order includes roughly 175 families and more than 15,000 described species (extant and extinct). Interpretations are complicated by the estimated 437 million years since origin of the Decapoda, with all the major lineages likely established by 325 million years ago. Constructing a molecular phylogeny across such a timescale requires markers with enough variation to infer relationships at the fi ne scale (at and within the family level) but which are conservative enough to refl ect deeper divergences across infraorders. Here we present a molecular phylogeny for the order Decapoda, combining nuclear and mitochondrial sequences, to investigate relationships among nine pleocyemate infraorders, one dendrobranchiate superfamily, 56 families, 113 genera, and 128 species. New and available sequence data are assembled to build the most extensive decapod phylogeny to date both in terms of taxon representation and genetic coverage. We discuss current and new hypotheses of decapod relationships and suggest a plan for the movement towards a consensus of decapod evolution.

Inventory of free-living freswater arthropods, with synonymical bibliography, occurring in the Pakistani fresh waters is drawn up, almost entirely from taxonomical literature checked until now. Six hundred and thirty two taxa have been recorded since 1892, of these 239 species and sub-species are of Crustacea, 368 species and sub-species are of Insecta, 25 species and sub-species are of Arachnida as well as few unidentified species. The present inventory is composed of the collated records from the publications of the library and internet. Totally 266 selected publications are arranged as resource references.

X-ray microtomography (XMT) was applied to three species of the extinct arachnid order Trigonotarbida, hosted in siderite nodules from the late Carboniferous British Middle Coal Measures. All three, Cryptomartus hindi (Pocock, 1911), Cleptomartus plautus (Petrunkevitch, 1949) and Maiocercus celticus (Pocock, 1902), belong to the family Anthracomartidae. As well as providing interactive three-dimensional visualisations of their likely appearance in life, XMT study has resolved new morphological detail, yielding key data about the likely stance and habitus of these early arachnids. Similarities in the form of the carapace, eyes and coxosternal region between anthracomartids and the Devonian genus PalaeocharinusHirst, 1923 are highlighted. Analogies in limb disposition are drawn between anthracomartids and modern crab spiders (Araneae: Thomisidae), which exhibit sit-and-wait style predatory behaviour. Anthracomartids are relatively common fossils at many Coal Measures localities. Although they appear to exhibit limited morphological variation, numerous genera and species have been proposed in the literature, often distinguished from each other on rather trivial characters. From our reconstruction of well-preserved examples, we have resolved a number of common features likely to be present in a typical anthracomartid. Comparisons to this model suggest that the characters on which many anthracomartid genera are distinguished may be artefacts of preservation. We hence treat PromygaleFrič, 1901, BrachylycosaFrič, 1904, PerneriaFrič, 1904, CoryphomartusPetrunkevitch, 1945, CryptomartusPetrunkevitch, 1945, PleomartusPetrunkevitch, 1945, CleptomartusPetrunkevitch, 1949 and OomartusPetrunkevitch, 1953 as junior synonyms of the type genus of the family, AnthracomartusKarsch, 1882. Only the genera BrachypygeWoodward, 1878 and MaiocercusPocock, 1911 are additionally retained. Within Anthracomartus, Cleptomartus planusPetrunkevitch, 1949, Cryptomartus meyeriGuthörl, 1964, Cleptomartus hangardiGuthörl, 1965 and Cryptomartus rebskeiBrauckmann, 1984 are treated as junior synonyms of A. hindiPocock, 1911 (all syn. nov.). Cleptomartus plautusPetrunkevitch, 1949 and Anthracomartus denuitiPruvost, 1922 are treated as junior synonyms of A. priestiPocock, 1911 (both syn. nov.).

Exceptionally preserved fossils from the Palaeozoic era provide crucial insights into arthropod evolution, with recent discoveries bringing phylogeny and character homology into sharp focus. Integral to such studies are anomalocaridids, a clade of stem arthropods whose remarkable morphology illuminates early arthropod relationships and Cambrian ecology. Although recent work has focused on the anomalocaridid head, the nature of their trunk has been debated widely.Here we describe new anomalocaridid specimens from the Early Ordovician Fezouata Biota of Morocco, which not only show well-preserved head appendages providing key ecological data, but also elucidate the nature of anomalocaridid trunk flaps, resolving their homology with arthropod trunk limbs. The new material shows that each trunk segment bears a separate dorsal and ventral pair of flaps, with a series of setal blades attached at the base of the dorsal flaps. Comparisons with other stem lineage arthropods indicate that anomalocaridid ventral flaps are homologous with lobopodous walking limbs and the endopod of the euarthropod biramous limb, whereas the dorsal flaps and associated setal blades are homologous with the flaps of gilled lobopodians (for example, Kerygmachela kierkegaardi,  Pambdelurion whittingtoni) and exites of the ‘Cambrian biramous limb’. This evidence shows that anomalocaridids represent a stage before the fusion of exite and endopod into the ‘Cambrian biramous limb’, confirming their basal placement in the euarthropod stem, rather than in the arthropod crown or with cycloneuralian worms. Unlike other anomalocaridids, the Fezouata taxon combines head appendages convergently adapted for filter-feeding with an unprecedented body length exceeding 2m, indicating a new direction in the feeding ecology of the clade. The evolution of giant filter-feeding anomalocaridids may reflect the establishment of highly developed planktic ecosystems during the Great Ordovician Biodiversification Event.

The discovery of the Fezouata biota in the latest Tremadocian of southeastern Morocco has significantly changed
our understanding of the early Phanerozoic radiation. The shelly fossil record shows a well-recognized pattern of macroevolutionary
stasis between the Cambrian Explosion and the Great Ordovician Biodiversification Event, but the rich soft-bodied
Fezouata biota paints a different evolutionary picture. The Fezouata assemblage includes a considerable component of
Cambrian holdovers alongside a surprising number of crown group taxa previously unknown to have evolved by the Early
Ordovician. Study of the Fezouata biota is in its early stages, and future discoveries will continue to enrich our view of the
dynamics of the early Phanerozoic radiation and of the nature of the fossil record.

A new aglaspidid arthropod, Chlupacaris dubia gen. et sp. nov., is described from the Pusgillian (lower Ashgill, Upper Ordovician) Upper Tiouririne Formation near Erfoud, southeastern Morocco. Although disarticulated, careful documenting of the tergites allows a reconstruction of the exoskeleton to be made. Although somewhat trilobite-like in appearance, the lack of facial sutures, a well-defined axis with articulating half-rings and a pygidium clearly prove Chlupacaris gen. nov. is not a trilobite. An interesting feature is the presence of a hypostome in this non-trilobite arthropod. In contrast to other aglaspidids usually considered to be carnivorous, a filter-feeding mode of life is proposed for Chlupacaris gen. nov., based on the strongly vaulted cephalon, subvertical orientation of the hypostome and less strongly vaulted trunk. Chlupacaris gen. nov. is probably most closely related to the atypical aglaspidid Tremaglaspis unite from the Tremadoc (Lower Ordovician) of the U.K., but it can also be tentatively linked to the problematic Lower Cambrian arthropods Kodymirus vagans and Kockurus grandis from the Czech Republic. The relevance and validity of previous definitions and of possibly significant characters used for identifying aglaspidids are evaluated, and as a result, a new combination of characters diagnosing Aglaspidida is proposed. Contrary to previous reports, it is suggested that aglaspidids are probably more closely related to trilobites than they are to chelicerates. This notion may be supported by the shared possession of a mineralised cuticle, a possibly similar number of cephalic appendages, and the presence of a hypostome in some forms, although this last character may alternatively be homoplastic.

Anomalocaridids, giant lightly sclerotized invertebrate predators,
occur in a number of exceptionally preserved early and middle
Cambrian (542–501 million years ago) biotas and have come to
symbolize the unfamiliar morphologies displayed by stem organisms in faunas of the Burgess Shale type. They are characterized by a pair ofanterior, segmented appendages, a circlet of plates around the mouth, and an elongate segmented trunk lacking true tergites with a pair of flexible lateral lobes per segment. Disarticulated body parts, such as the anterior appendages and oral circlet, had been assigned to a range of taxonomic groups—but the discovery of complete specimens from the middle Cambrian Burgess Shale showed that these disparate elements all belong to a single kind of animal. Phylogenetic analyses support a position of anomalocaridids in the arthropod stem, as a sister group to the euarthropods. The anomalocaridids were the largest animals in Cambrian communities. The youngest unequivocal examples occur in the middle Cambrian Marjum Formation of Utah but an arthropod retaining some anomalocaridid characteristics is present in the Devonian of Germany. Here we report the post-Cambrian occurrence of anomalocaridids, from the Early Ordovician (488–472 million years ago) Fezouata Biota in southeastern Morocco, including specimens larger than any in Cambrian biotas. These giant animals were an important element of some marine communities for about 30 million years longer than previously realized. The Moroccan specimens confirm the presence of a dorsal array of flexible blades attached to a transverse rachis on the trunk segments; these blades probably functioned as gills.

Fossil age data and molecular sequences are increasingly combined to establish a timescale for the Tree of Life. Arthropods, as the most species-rich and morphologically disparate animal phylum, have received substantial attention, particularly with regard to questions such as the timing of habitat shifts (e.g. terrestrialisation), genome evolution (e.g. gene family duplication and functional evolution), origins of novel characters and behaviours (e.g. wings and flight, venom, silk), biogeography, rate of diversification (e.g. Cambrian explosion, insect coevolution with angiosperms, evolution of crab body plans), and the evolution of arthropod microbiomes. We present herein a series of rigorously vetted calibration fossils for arthropod evolutionary history, taking into account recently published guidelines for best practice in fossil calibration. These are restricted to Palaeozoic and Mesozoic fossils, no deeper than ordinal taxonomic level, nonetheless resulting in 80 fossil calibrations for 102 clades. This work is especially timely owing to the rapid growth of molecular sequence data and the fact that many included fossils have been described within the last five years. This contribution provides a resource for systematists and other biologists interested in deep-time questions in arthropod evolution.

The Weeks Formation in Utah is the youngest (c. 499 Ma) and least studied Cambrian Lagerstätte of the western USA. It preserves a diverse, exceptionally preserved fauna that inhabited a relatively deep water environment at the offshore margin of a carbonate platform, resembling the setting of the underlying Wheeler and Marjum formations. However, the Weeks fauna differs significantly in composition from the other remarkable biotas of the Cambrian Series 3 of Utah, suggesting a significant Guzhangian faunal restructuring. This bioevent is regarded as the onset of a transitional episode in the history of life, separating the two primary diversifications of the Early Paleozoic. The Weeks fossils have been strongly affected by late diagenetic processes, but some specimens still preserve exquisite anatomical details. Supplementary material: a supplementary text (material and methods), four supplementary tables (compositions of the lower and upper Weeks faunas, structure of the upper Weeks fauna, and results of the similarity analyses), and a supplementary data file (generic presence/absence matrix) are available at https://doi.

When I found the first fossil... I knew right away that it was an arthropod with paired appendages, extending forward, as if it was swimming on the moistened surface of a mudstone. But I realized that you could see the impression of the soft body parts. That night I put the fossils under my bed. But because I was so excited, I couldn't sleep very well. I got up often and pulled out the fossils just to look at them.

Backobourkia, a new Australasian genus of orb-weaving spider (family Araneidae Clerck, 1758) is proposed with Backobourkia heroine (L. Koch, 1871) as type species. Two other species are included in the genus: B. brounii (Urquhart, 1885) comb. nov. (here removed from synonymy with B. heroine) and B. collina ) comb. nov. (= Araneus reversus Hogg, 1914. A phylogenetic analysis places Backobourkia within the 'coxal hook clade' of the subfamily Araneinae Clerck, 1758 and close to Eriophora Simon, 1864; however, Backobourkia differs from other Australasian Araneinae by the proposed synapopomorphy of a long fl ange at the base of the median apophysis in males. Molecular phylogenetic analysis of a fragment of the mitochondrial gene cytochrome c oxidase subunit 1 (COI) supports the monophyly of Backobourkia in a limited dataset that includes exemplars of Australasian Araneidae and Eriophora ravilla (C.L. Koch, 1844) (type species of Eriophora Simon, 1864). Backobourkia brounii and B. heroine are sister taxa in this analysis. Backobourkia collina is unusual within the genus and amongst most Araneinae as it displays extreme sexual size dimorphism (SSD), with females on average more than four times the size of males. Comparison with the other two Backobourkia species (and other Araneinae) suggests male dwarfi sm rather than female gigantism for this SSD. Some morphological differences of B. collina males to its congeners are evident, possibly due to its reduced size. These include characters of putative phylogenetic signal at the genus level such as eye position, shape of male pedipalp sclerites and the absence or presence of endite teeth or coxal hooks. Backobourkia species are common throughout Australia, with B. heroine more prevalent in the western and B. brounii in the eastern parts of the country. Backobourkia collina is mainly found throughout the arid regions. Backobourkia brounii is also found in New Zealand and B. heroine in New Caledonia. Araneus felinus (Butler, 1876), originally described as 'Allied to E. heroine', is here considered a nomen dubium as the type specimen appears to be lost and an accurate identifi cation based on the original description is not possible. The New Zealand Eriophora decorosa (Urquhart, 1894) is transferred to Acroaspis Karsch, 1878, A. decorosa (Urquhart, 1894) comb. nov.

Pectines are unique, midventral sensory appendages that help direct mating and food-finding behaviors in scorpions. Dense two-dimensional arrays of bimodally sensitive (chemical and mechanical) peg sensilla form the primary sensory structures on pectines. Several qualities of peg sensilla make them well suited to electrophysiological investigation, including accessibility, stability of extracellular recordings, and the ease with which spiking cells can be identified and categorized. Cross-correlations of spontaneous neural activity show signs of synaptic interactions between sensillar neurons in all species examined to date (Paruroctonus mesaensis, Hadrurus arizonensis, Centruroides vittatus) representing three families and two superfamilies. Both excita-tory and inhibitory interactions have been observed, as well as possible dyadic synaptic arrange-ment. Computer simulations of cross-correlograms are consistent with experimental data and may help provide additional insight into fun...

The enigmatic Upper Carboniferous arthropod genus Camptophyllia is known from 11 fossils, found at five Coal Measures Lagerstätten. These siderite-hosted fossils reveal only the organism's dorsal surface – its ventral and appendage morphology is entirely unknown, hampering efforts to place the genus taxonomically or phylogenetically. This study reports the application of high-resolution X-ray micro-tomography (XMT) to six Camptophyllia specimens, from four Carboniferous Lagerstätten. This XMT-based restudy has provided new morphological detail, confirming the anteriormost segment is cephalic and facilitating more informed speculation regarding the organism's mode of life. However, despite scanning all but one of the known representatives of the genus, ventral anatomy has not been resolved; it is possible this is taphonomic, resulting from a poorly sclerotized ventral region. Pending the discovery of further material, the affinities of Camptophyllia remain unclear.

The basic arrangement of limbs in euarthropods consists of a uniramous head appendage followed by a series of biramous appendages. The body is divided into functional units or tagmata which are usually distinguished by further differentiation of the limbs. The living horseshoe crabs are remnants of a much larger diversity of aquatic chelicerates. The limbs of the anterior and posterior divisions of the body of living horseshoe crabs differ in the loss of the outer and inner ramus, respectively, of an ancestral biramous limb. Here we report a new fossil horseshoe crab from the mid-Silurian Lagerstätte in Herefordshire, United Kingdom (approximately 425 Myr B.P.), a site that has yielded a remarkably preserved assemblage of soft-bodied fossils. The limbs of the new form can be homologized with those of living Limulus, but retain an ancestral biramous morphology. Remarkably, however, the two limb branches originate separately, providing fossil evidence to suggest that repression or loss of gene expression might have given rise to the appendage morphology of Limulus. Both branches of the prosomal limbs of this new fossil are robust and segmented in contrast to their morphology in Cambrian arthropods, revealing that a true biramous limb was once present in chelicerates as well as in the mandibulates.

Fossil age data and molecular sequences are increasingly combined to establish a timescale for the 15 Tree of Life. Arthropods, as the most species-rich and morphologically disparate animal phylum, have 16 received substantial attention, particularly with regard to questions such as the timing of habitat shifts 17 (e.g. terrestrialisation), genome evolution (e.g. gene family duplication and functional evolution), 18 origins of novel characters and behaviours (e.g. wings and flight, venom, silk), biogeography, rate of 19 diversification (e.g. Cambrian explosion, insect coevolution with angiosperms, evolution of crab body 20 plans), and the evolution of arthropod microbiomes. We present herein a series of rigorously vetted 21 calibration fossils for arthropod evolutionary history, taking into account recently published guidelines 22 for best practice in fossil calibration. These are restricted to Palaeozoic and Mesozoic fossils, no 23 deeper than ordinal taxonomic level, nonetheless resulting in 80 fossil calibrations for 102 clades. This 24 work is especially timely owing to the rapid growth of molecular sequence data and the fact that many 25 included fossils have been described within the last five years. This contribution provides a resource 26 A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT 2 for systematists and other biologists interested in deep-time questions in arthropod evolution. ACCEPTED MANUSCRIPT 4 et al., 2014; Wheat and Wahlberg, 2013), evolution of parasites and disease (Ibarra-Cerdeña et al., 79 2014; Palopoli et al., 2014; Rees et al., 2014; Zhou et al., 2014), rate of diversification and its 80 relationship to morphology and ecology (Lee et al., 2013; Wiens et al., 2015), coevolution (Kaltenpoth 81 et al., 2014; Shelomi et al., 2016; Wilson et al., 2013), conservation (Owen et al., 2015), and the use 82 of arthropods as a model for methodological development (O'Reilly et al., 2015; Ronquist et al., 2012; 83 Warnock et al., 2012; Zhang et al., 2016). 84 Recent consensus on best practices for selecting calibration fossils comes with several 85 requirements. There must be references to specific fossil specimen(s), phylogenetic or morphological 86 evidence justifying placement of the fossil, and stratigraphic and/or radiometric dating information for 87 the fossil (Parham et al., 2012). The importance of accurate phylogenetic knowledge of calibration 88 fossils is underscored by recent controversies in dating the evolution of insects, where arguments 89 hinge on the classification of particular 'roachoid' fossils on the stem lineage of Dictyoptera, with 90 resulting differences on the order of 100 Myr (Kjer et al., 2015; Tong et al., 2015). With the explosion of 91 taxonomic sampling in molecular phylogenies due to improvements in sequencing technology, 92 improving the coverage of fossil calibrations is equally important. Recommendations include, for 93 example, including as many as one fossil per ten extant taxa for precise ages, with a varied 94 distribution across lineages and clade depth (Bracken-Grissom et al., 2014). As a response, we have 95 compiled an atlas of 80 rigorously scrutinized calibration fossils for 102 key nodes in arthropod 96 phylogeny. These represent four basal ecdysozoan and arthropod clades, 17 chelicerates, 12 97 myriapods, 30 non-hexapod pancrustaceans, and 39 hexapod clades.

A new exceptionally preserved marginal marine biota is reported from the Late Ordovician Big Hill Formation of Stonington Peninsula in Michigan's Upper Peninsula. The new Lagerstätte hosts a moderately diverse fauna of medusae, linguloid brachiopods, non-mineralized arthropods and orthocone nautiloids, alongside dasycladalean green algae. The biota is similar to those of Lagerstätten from the Late Ordovician of Canada, revealing an extensive distribution of a distinctive marginal marine palaeocommunity in Laurentia at this time. The Big Hill biota extends the geographical range of exceptionally preserved Late Ordovician faunas in Laurentia and indicates that further examples remain to be discovered.

A new aglaspidid euarthropod with a six-segmented trunk from the Lower Ordovician Fezouata Konservat-Lagerstätte, Morocco Abstract – A new euarthropod with an uncommon morphology, Brachyaglaspis singularis gen. et sp. nov., is described from the Early Ordovician (middle Floian) Fezouata biota of Morocco. The presence of a pair of postventral plates, widely attached to each other and located under the posterior-most trunk tergite and the base of the tailspine, indicates a phylogenetic relationship with the enigmatic group Aglaspidida. The overall morphology of Brachyaglaspis most closely resembles that of the 'Ordovician-type' aglaspidids, more specifically the late Cambrian – Early Ordovician genus Tremaglaspis. However, the presence of a prominent cephalon and only six trunk tergites in the new genus deviates from the organization of all other known aglaspidid species, notably extending the known range of morphological disparity of the group. A taxonomic revision of this euarthropod group indicates that the most accurate name and authorship combination correspond to Aglaspidida Walcott, 1912.

A single specimen of a new species of the chasmata-spidid Diploaspis Størmer, 1972 is described from the upper Silurian (Pridoli) Phelps Member of the Fiddlers Green Formation (Bertie Group) in Herkimer County, New York State, USA. Diploaspis praecursor sp. nov. is distinguished by the shape of the posterolateral margins of the buckler, which are drawn out into angular epimera, and by the lack of elongate tubercles on the postabdomen. This discovery increases the taxonomic diversity of the Bertie Group by extending the geographic extent of Diploaspididae into North America. D. praecursor pre-dates previously known species of Diploaspis by more than 10 million years.

The Carboniferous eurypterid Eurypterus dumonti STAINIER, 1917 from Mechelen-aan-de-Maas (Maasmechelen), Belgium is redescribed and assigned to the genus Adelophthalmus. It is diagnosed as having a raised triangle of unknown function, dorsally on opisthosomal segment 7 and a carapace articulating laterally against the second opisthosomal segment. Earlier assignments of this species to the genus Unionopterus, based on the carapace shape figured in the original description (STAINIER 1917), are incorrect and the existence of a Carboniferous eurypterid with the characteristics described for Unionopterus must be questioned. The appendages in A. dumonti are completely exposed and provide an unrivalled insight into the number of appendage podomeres in the genus; this species is interpreted to have a podomere count consistent with most other eurypterids. Small pustules previously thought to be cuticle sculpture are here interpreted as diagenetic``dumb-bells'' (see BRIGGS & WILBY 1996) following microbial activity on the carcase prior to fossilisation. Thesè`dumb-bells'' are the oldest non-marine record of this diagenetic feature. A number of other features are also interpreted differently from the original description. Possible lineages within the Adelophthalmus clade are identified, A. dumonti is probably closely related to A. imhofi (Czech Republic) and A. moyseyi (United Kingdom).

Specimens of Euproops sp. (Xiphosura, Chelicerata)
from the Carboniferous Piesberg quarry near Osnabrück,
Germany, represent a relatively complete growth series of 10
stages. Based on this growth sequence, morphological changes
throughout the ontogeny can be identified. The major change
affects the shape of the epimera of the opisthosoma. In earlier
stages, they appear very spine-like, whereas in later stages the
bases of these spine-like structures become broader; the broadened bases are then successively drawn out distally. In the most mature stage known, the epimera are of trapezoidal shape and approach each other closely to form a complete flange around the thoracetron (fused tergites of the opisthosoma). These ontogenetic changes question the taxonomic status of different species of Euproops, as the latter appear to correspond to different stages of the ontogenetic series reconstructed from the Piesberg specimens. This means that supposed separate species could, in fact, represent different growth stages of a single species. It could alternatively indicate that heterochrony (evolutionary change of developmental timing) plays an important role in the evolution of Xiphosura. We propose a holomorph approach, i.e., reconstructing ontogenetic sequences for fossil and extant species as a sound basis for a taxonomic, phylogenetic, and evolutionary discussion of Xiphosura.

Background

Few studies on eurypterids have taken into account morphological changes that occur throughout postembryonic development. Here two species of eurypterid are described from the Pragian Beartooth Butte Formation of Cottonwood Canyon in Wyoming, and included in a phylogenetic analysis. Both species comprise individuals from a number of instars, and this allows for changes that occur throughout their ontogeny to be documented, and how ontogenetically variable characters can influence phylogenetic analysis to be tested.
Results

The two species of eurypterid are described as Jaekelopterus howelli (Kjellesvig-Waering and Størmer, 1952) and Strobilopterus proteus sp. nov. Phylogenetic analysis places them within the Pterygotidae and Strobilopteridae respectively, both families within the Eurypterina. Jaekelopterus howelli shows positive allometry of the cheliceral denticles throughout ontogeny, while a number of characteristics including prosomal appendage length, carapace shape, lateral eye position, and relative breadth all vary during the growth of Strobilopterus proteus.
Conclusions

The ontogeny of Strobilopterus proteus shares much in common with that of modern xiphosurans, however certain characteristics including apparent true direct development suggest a closer affinity to arachnids. The ontogenetic development of the genital appendage also supports the hypothesis that the structure is homologous to the endopods of the trunk limbs of other arthropods. Including earlier instars in the phylogenetic analysis is shown to destabilise the retrieved topology. Therefore, coding juveniles as individual taxa in an analysis is shown to be actively detrimental and alternative ways of coding ontogenetic data into phylogenetic analyses should be explored.

The order Decapoda represents a species-rich group of crustaceans. Numerous economically important and morphologically diverse members of this group have been studied extensively for many decades, in part to understand their phylogeny. There are several competing hypotheses concerning relationships among the major lineages of Decapoda. Our laboratories are estimating a robust decapod phylogeny based on molecular and morphological data in an attempt to resolve relationships among major lineages. The order includes roughly 175 families and more than 15,000 described species (extant and extinct). Interpretations are complicated by the estimated 437 million years since origin of the Decapoda, with all the major lineages likely established by 325 million years ago. Constructing a molecular phylogeny across such a timescale requires markers with enough variation to infer relationships at the fi ne scale (at and within the family level) but which are conservative enough to refl ect deeper divergences across infraorders. Here we present a molecular phylogeny for the order Decapoda, combining nuclear and mitochondrial sequences, to investigate relationships among nine pleocyemate infraorders, one dendrobranchiate superfamily, 56 families, 113 genera, and 128 species. New and available sequence data are assembled to build the most extensive decapod phylogeny to date both in terms of taxon representation and genetic coverage. We discuss current and new hypotheses of decapod relationships and suggest a plan for the movement towards a consensus of decapod evolution.

Two new polyneopteran insect nymphs from the Montceau-les-Mines Lagerstätte of France are presented. Both are preserved in three dimensions, and are imaged with the aid of X-ray micro-tomography, allowing their morphology to be recovered in unprecedented detail. One–Anebos phrixos gen. et sp. nov.–is of uncertain affinities, and preserves portions of the antennae and eyes, coupled with a heavily spined habitus. The other is a roachoid with long antennae and chewing mouthparts very similar in form to the most generalized mandibulate mouthparts of extant orthopteroid insects. Computer reconstructions reveal limbs in both specimens, allowing identification of the segments and annulation in the tarsus, while poorly developed thoracic wing pads suggest both are young instars. This work describes the morphologically best-known Palaeozoic insect nymphs, allowing a better understanding of the juveniles’ palaeobiology and palaeoecology. We also consider the validity of evidence from Palaeozoic juvenile insects in wing origin theories. The study of juvenile Palaeozoic insects is currently a neglected field, yet these fossils provide direct evidence on the evolution of insect development. It is hoped this study will stimulate a renewed interest in such work

Ecosystem engineering is a process by which organisms change the distribution of resources and create new habitats for other species via non-trophic interactions. Leaf-rolling caterpillars can act as ecosystem engineers because they provide shelter to secondary users. In this study, we report the influence of leaf-rolling caterpillars on speciose tropical arthropod communities along both spatial scales (leaf-level and plant-level effects) and temporal scales (dry and rainy seasons). We predict that rolled leaves can amplify arthropod diversity at both the leaf and plant levels and that this effect is stronger in dry seasons, when arthropods are prone to desiccation. Our results show that the abundance, richness, and biomass of arthropods within several guilds increased up to 22-fold in naturally and artificially created leaf shelters relative to unaltered leaves. These effects were observed at similar magnitudes at both the leaf and plant scales. Variation in the shelter architecture (funnel, cylinders) did not influence arthropod parameters, as diversity, abundance, or biomass, but rolled leaves had distinct species composition if compared with unaltered leaves. As expected, these arthropod parameters on the plants with rolled leaves were on average approximately twofold higher in the dry season. Empty leaf rolls and whole plants were rapidly recolonized by arthropods over time, implying a fast replacement of individuals; within 15-day intervals the rolls and plants reached a species saturation. This study is the first to examine the extended effects of engineering caterpillars as diversity amplifiers at different temporal and spatial scales. Because shelter-building caterpillars are ubiquitous organisms in tropical and temperate forests, they can be considered key structuring elements for arthropod communities on plants.

The biologically and geologically extremely diverse archipelagos of Wallacea, Australasia and Oceania have long stimulated ecologists and evolutionary biologists. Yet, few molecular phylogenetic analyses of the terrestrial fauna have been carried out to understand the evolutionary patterns. We use dense taxon and character sampling of more than 7000 bp DNA sequence data for a group of diving beetles ranging from the Holarctic throughout Asia to as far east as French Polynesia. We here show that an ecologically diverse, common and widespread (Portugal to New Zealand) arthropod supertramp species originated in the highlands of New Guinea, ca 6.0–2.7 Myr ago. The approximately 25 closely related species are narrow endemics in Australasia/Oceania. The ancestor of this clade colonized that region from Eurasia ca 9–7 Myr ago. Our finding contradicts the widely held view of local endemism as an evolutionary dead end, as we find multiple peripatric speciation events within the Pleistocene a...

Sampling was conducted at four different sites i.e., an agricultural field, a river basin, a brick field and a forest floor from the district of Uttar Dinajpur, West Bengal, India. Though abundance was higher at the forest site, the group diversities during summer, monsoon and post-monsoon seasons were highest at the river basin. Site-specific and temporal variation of abundance was significant among the sites (p<0.05).

The order Decapoda represents a species-rich group of crustaceans. Numerous economically important and morphologically diverse members of this group have been studied extensively for many decades, in part to understand their phylogeny. There are several competing hypotheses concerning relationships among the major lineages of Decapoda. Our laboratories are estimating a robust decapod phylogeny based on molecular and morphological data in an attempt to resolve relationships among major lineages. The order includes roughly 175 families and more than 15,000 described species (extant and extinct). Interpretations are complicated by the estimated 437 million years since origin of the Decapoda, with all the major lineages likely established by 325 million years ago. Constructing a molecular phylogeny across such a timescale requires markers with enough variation to infer relationships at the fi ne scale (at and within the family level) but which are conservative enough to refl ect deeper divergences across infraorders. Here we present a molecular phylogeny for the order Decapoda, combining nuclear and mitochondrial sequences, to investigate relationships among nine pleocyemate infraorders, one dendrobranchiate superfamily, 56 families, 113 genera, and 128 species. New and available sequence data are assembled to build the most extensive decapod phylogeny to date both in terms of taxon representation and genetic coverage. We discuss current and new hypotheses of decapod relationships and suggest a plan for the movement towards a consensus of decapod evolution.

ABSTRACT: Previously enigmatic, ovoid to sac-like fossils of organic, acid resistant substance which are common components of leaf cuticle and megaspore assemblages in limnic and terrestrial palaeoen- vironments are identified as cocoons of clitellates. They have been recorded for a long time by palaeobotanists and palynologists, particularly in the Mesozoic, and have been variously interpreted as being of megaspore, seed, or algal origins, although convincing homologues were lacking. The fossils agree in basic wall construction with cocoons of clitellates, and particularly with certain members of the Hirudinea. A clitellate affinity is further supported by a possible segmentation, their consistently non-marine occurrence, evidence for predation, and an example of amber-like inclusion of alien structures in the cocoon wall which indicates the presence of secretion. As a consequence of the new interpretation, two taxa established under the botanical code of nomenclature for such fossils, namely Burejospermum crassitestum Krassilov and Dictyoth- ylakos pesslerae Horst, are transferred to the zoological kingdom and classified under Clitellata (phylum Annelida), along with two new taxa, D. spitsbergensis sp.n. andPilothylakospilosus gen. et sp.n. With the present interpretation a consistent Mesozoic record is documented for clitellates, a group of softbodied, basically freshwater and terrestrial animals of which there was until now nearly no fossil record.

Specimens of Euproops sp. (Xiphosura, Chelicerata) from the Carboniferous Piesberg quarry near Osnabrück, Germany, represent a relatively complete growth series of 10 stages. Based on this growth sequence, morphological changes throughout the ontogeny can be identified. The major change affects the shape of the epimera of the opisthosoma. In earlier stages, they appear very spine-like, whereas in later stages the bases of these spine-like structures become broader; the broadened bases are then successively drawn out distally. In the most mature stage known, the epimera are of trapezoidal shape and approach each other closely to form a complete flange around the thoracetron (=fused tergites of the opisthosoma). These ontogenetic changes question the taxonomic status of different species of Euproops, as the latter appear to correspond to different stages of the ontogenetic series reconstructed from the Piesberg specimens. This means that supposed separate species could, in fact, represent different growth stages of a single species. It could alternatively indicate that heterochrony (=evolutionary change of developmental timing) plays an important role in the evolution of Xiphosura. We propose a holomorph approach, i.e., reconstructing ontogenetic sequences for fossil and extant species as a sound basis for a taxonomic, phylogenetic, and evolutionary discussion of Xiphosura.

Late Cambrian arthropod trackways from the Potsdam Sandstone have been known since the 1850s. A site in Clinton County, New York, USA, exposes _Protichnites_ in fine-grained, quartz-rich, rippled, micro-laminated Potsdam Sandstone. The study area includes evidence of microbial mat growth on the original surface where the trackways were produced. Ripple marks presumably underlie, and therefore were generated prior to, the microbial mat. Trackway preservation is variable over the outcrop and depositional setting indicates a high intertidal or a low supratidal environment with growth of benthic microbial mats. At least eleven distinguishable trackways of multi-legged, telson- bearing individuals show a range of widths. The trackways consist of repetitive sets of seven pairs of tracks converging in the direction of motion of the organism. A telson impression, either discontinuous or continuous, divides the trackways longitudinally and is nearly centered throughout the lengths of the tra...

Recently, we proposed a hierarchical model for the elastic properties of mineralized lobster cuticle using (i) ab initio calculations for the chitin properties and (ii) hierarchical
homogenization performed in a bottom-up order through all length scales. It has been found that the cuticle possesses nearly extremal, excellent mechanical properties in terms of stiffness that strongly depend on the overall mineral content and the specific microstructure of the mineral–protein matrix. In this study, we investigated how the overall cuticle properties changed when there are significant variations in the properties of the constituents (chitin, amorphous calcium carbonate (ACC), proteins), and the volume fractions of key structural elements such as chitin–protein fibers. It was found that the cuticle performance is very robust with respect to variations in the elastic properties of chitin and fiber proteins at a lower hierarchy level. At higher structural levels, variations of design parameters such as the volume fraction of the chitin–protein fibers have a significant influence on the cuticle performance. Furthermore, we observed that among the possible variations in the cuticle ingredients and volume fractions, the experimental data reflect an optimal use of the structural variations regarding the best possible performance for a given composition due to the smart hierarchical organization of the cuticle design.

Changing scenario of climate resulting from global warming and adversity of nature has also resulted in emergence and re-emergence of diseases transmitted by arthropods. Increasing trends of population growth of dogs has increased the chance of disease transmission due to readily available susceptible host. Babesiosis and Hepatozoonosis and Ehrlichiosis are the main arthropod borne diseases of dogs prevalent in India. The present article explains the importance of these arthropod transmitted infections in kennel dogs, research progress and reason for their emergence in the present scenario.

The Weeks Formation in Utah is the youngest (c. 499 Ma) and least studied Cambrian Lagerstätte of the western USA. It preserves a diverse, exceptionally preserved fauna that inhabited a relatively deep water environment at the offshore margin of a carbonate platform, resembling the setting of the underlying Wheeler and Marjum formations. However, the Weeks fauna differs significantly in composition from the other remarkable biotas of the Cambrian Series 3 of Utah, suggesting a significant Guzhangian faunal restructuring. This bioevent is regarded as the onset of a transitional episode in the history of life, separating the two primary diversifications of the Early Paleozoic. The Weeks fossils have been strongly affected by late diagenetic processes, but some specimens still preserve exquisite anatomical details.Supplementary material: a supplementary text (material and methods), four supplementary tables (compositions of the lower and upper Weeks faunas, structure of the upper Weeks...

The dramatic increase in soil degradation in the last few decades has led to the need to identify methods to define not only soil quality but also, in a holistic approach, soil health. In the past twenty years, indices based on living communities have been proposed alongside the already proven physical-chemical methods. Among them, some soil invertebrates have been included in monitoring programs as bioindicators of soil quality. Being an important portion of soil fauna, soil arthropods are involved in many soil processes such as organic matter decomposition and translocation, nutrient cycling, microflora activity regulation and bioturbation. Many studies have reported the use of soil arthropods to define soil quality; among taxa, some have been explored more in depth, typically Acari and Collembola, while generally less abundant groups, such as Palpigradi or Embioptera, have not been investigated much. This paper aims to evaluate and compare the use of different soil microarthropod...

DNA sequences offer powerful tools for describing the members and interactions of natural communities. In this paper, we establish the to-date most comprehensive library of DNA barcodes for a terrestrial site, including all known macroscopic animals and vascular plants of an intensively-studied area of the High Arctic, the Zackenberg Valley in Northeast Greenland. To demonstrate its utility, we apply the library to identify nearly 20 000 arthropod individuals from two Malaise traps, each operated for two summers. Drawing on this material, we estimate the coverage of previous morphology-based species inventories, derive a snapshot of faunal turnover in space and time, and describe the abundance and phenology of species in the rapidly changing arctic environment. Overall, 403 terrestrial animal and 160 vascular plant species were recorded by morphology-based techniques. DNA barcodes (CO1) offered high resolution in discriminating among the local animal taxa, with 92% of morphologicall...

We describe a compound trace fossil Stiaria cf. intermedia C Avolatichnium isp. from the lower
Permian of Southern Alps (North Italy) and confidently attribute it to a wingless (apterygote)
jumping insect producer belonging to the order Monura (Insecta: Archaeognatha). We discuss the
common features linking the ichnogenera Avolatichnium, Rotterodichnium and Tonganoxichnus, and
suggest a close affinity for their producers. Grounded on previous studies and on some exceptional
features preserved in the described material, we provide a biomechanical model for jumping in
Archaeognatha and hypothesize that Paleozoic Archaeognatha performed jumps with high vertical
and very low horizontal component and only later acquired the ability to heighten the horizontal
component of their jumps, therefore, becoming more efficient in propelling themselves far ahead
as extant species do.