An early form of eurypterids (Chelicerata), Archopterus anjiensis n. gen. n. sp., is described from the uppermost Ordovician Wenchang Formation of Anji County, Zhejiang Province, South China. It is the earliest record of eurypterids in China and likely the oldest representative of the Adelophthalmidae. The species, represented by a single specimen, is diagnosed by a ventrally preserved prosoma with a parabolic carapace, Hughmilleria-type prosomal appendages, a short vase-shaped metastoma, and a three-segmented type A (female) genital appendage. The specimen is preserved, together with diverse sponges, graptolites and occasional nautiloids, in a 10 m thick shale of marine deep-water setting. This finding extends the stratigraphic range of adelophthalmids from the previously recorded early Silurian into the Late Ordovician (some 10 million years older) and supports an earlier cryptic phase of eurypterid evolution in Gondwana.

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Palmichnium gallowayi (Sharpe, 1932) new combination from the Middle Ordovician Martinsburg Formation (proximal deltaic facies) of Rondout, near Kingston, New York State, is redescribed. It consists of opposing series of five tracks, the outer two large and pear-shaped, the inner three smaller and elliptical, arranged in a chevron converging in the direction of travel, on either side of a wide medial impression. It is attributed to a medium-sized stylonurid eurypterid using a decapodous gait, crawling onto the shoreline, traversing the intertidal zone, a behavior interpreted as part of its reproductive life cycle. This provides the earliest ichnological evidence for the ‘mass-molt-mate’ hypothesis, which proposes that eurypterids migrated en masse into nearshore environments to molt and mate.

A new genus and species of eurypterid (Eurypterida: Chelicerata) is described as Orcanopterus manitoulinensis from the Upper Ordovician Kagawong Submember (Upper Member) of the Georgian Bay Formation, Manitoulin Island, Ontario, Canada. The material comprises several partial specimens in addition to disarticulated carapaces, appendages, metastomas, opisthosomal segments, and telsons. Associated fossils include rare bryozoans, a conularid, ostracodes, and conodonts. A restricted marine lagoon, or very shallow subtidal to intertidal environment is inferred. This assemblage, perhaps representing an accumulation of molted exuviae, was apparently preserved as the result of rapid burial by carbonate muds and silts during a storm event. O. manitoulinensis shares a number of traits with both the Hughmilleriidae and the Carcinosomatidae. Diagnostic features include curved preabdominal segments, a petaloid A metastoma with deep anterior emargination, spiniferous appendages of Carcinosoma type, paddle with enlarged, symmetrical podomere 9, and a xiphous telson. It is only the fourth (the first Canadian) well-documented Ordovician eurypterid genus, and provides the oldest reliable record of the Hughmillerioidea to date.

A new synziphosurine (Chelicerata: Xiphosura) is described from the Late Llandovery (Silurian) Konservat-Lagerstätte of Waukesha, Wisconsin, USA. Venustulus waukeshaensis n.gen. and sp. is characterized by a semicircular carapace with a slightly procurved posterior margin lacking genal spines and an opisthosoma composed of 10 freely articulating segments, divided into a preabdomen of seven segments with blunt pleurae and a postabdomen of three segments lacking pleurae. The tail spine is short and styliform. This is the earliest known unequivocal synziphosurine, extending their fossil record from the Wenlock to the Llandovery, and only the second species to be described with prosomal appendages; the presence of six pairs (a pair of chelicerae and five pairs of walking legs) contrasts with the seven in the synziphosurine Weinbergina opitzi, but is comparable to the number in modern horseshoe crabs. V. waukeshaensis n. gen. and sp. is not assigned to a family here pending a wider revision, but it bears most resemblance to the Weinberginidae.

Stomatopods, or mantis shrimps, are malacostracan crustaceans. Known as “lean, mean, killing machines” (Watling et al., 2000, p. 1), modern stomatopods are obligate carnivores, feeding exclusively on live prey (Schram, 1986). Characteristically, their second thoracic appendages are enlarged to form powerful, raptorial claws. Modern stomatopods are divided into two broad functional groups based on the shape and usage of their raptorial claws: ‘spearing’ and ‘smashing’ stomatopods (Caldwell and Dingle, 1976).

New Mexico contains a significant record of trace fossil assemblages, in terms of both abundance and ichnodiversity, from Lower Permian nonmarine depositional settings. Most notable amongst these are the trace fossil assemblages in the Robledo Mountains Formation of the Robledo Mountains in Doña Ana County, southern New Mexico, as recognized by the recent proposal to designate this area as a national monument. These trace fossil assemblages formed on a tidal flat under largely non-marine conditions (Mack and James, 1986; Hunt et al., 1993; Lucas et al., 1995a, 1998) and are dominated by the trackways of tetrapods and arthropods, yielding important information on the paleoecology, diversity and behavior of late Paleozoic arthropods (Braddy and Briggs, 2002; Minter and Braddy, 2006a), as well as evidence of specialized foraging strategies (Minter et al., 2006). Additional Lower Permian trace fossil assemblages occur at a number of localities in New Mexico and represent a variety of nonmarine depositional settings.

A new genus and species of synziphosurine (Chelicerata) is described from the Silurian (Wenlock) Scotch Grove Formation Konservat-Lagerstätte in Clinton County, Iowa. Camanchia grovensis n. gen. n. sp. is characterized by a sub-triangular carapace, ten opisthosomal segments divided into a preabdomen of seven and a postabdomen of three, and a tuberculate ornament on the carapace and pleural margins. A single new specimen from the same location is assigned to Venustulus waukeshaensis, originally described from the Late Llandovery Waukesha Konservat-Lagerstätte of Wisconsin. A comparison of the musculature of C. grovensis with that of living Limulus polyphemus and the Jurassic Mesolimulus walchi from Nusplingen, Germany shows that it is much simpler, consistent with the status of synziphosurines as stem xiphosurids.

The Lower Permian (Late Wolfcampian) marginal marine facies of the Robledo Mountains Member (Hueco Formation) of the Robledo Mountains, New Mexico, contains a diverse ichnofauna dominated by vertebrate trackways. Four new arthropod ichnotaxa are described. Tonganoxichnus robledoensis new ichnospecies, consists of repeated small traces comprising imprints of anteriorly directed legs, an elongate tapering abdomen, and a thin tail. Hedriumichnus apacheensis new ichnogenus and ichnospecies consists of isolated small traces comprising imprints of laterally-directed legs, a broad tapering abdomen, and a short tail. Rotterodichnium major new ichnospecies is a large trace with imprints of the head and thorax, a long thin abdomen and three pairs of legs, increasing in length posteriorly. Quadrispinichna parvia new ichnogenus and ichnospecies consists of four diverging or sub-parallel linear or curvilinear imprints of approximately equal length.

Tonganoxichnus, previously known from the Upper Carboniferous of eastern Kansas, is interpreted as produced by a jumping monuran (an extinct group of wingless insects). Hedriumichnus, known only from the Robledo Mountains, is interpreted as the resting trace of a nymph of a primitive Ephemeroptera or Plecoptera. Rotterodichnium, previously known from the Lower Permian of Germany, is interpreted as the resting trace of a large dragonfly-like form (Protodonata, Odonata, or Megasecoptera). Quadrispinichna, previously recorded but not named, from the Lower Permian Ecca succession of South Africa, is interpreted as a resting trace of a crustacean. These rare traces increase our understanding of the diversity and behavior of nonmarine arthropod communities in the Lower Permian.

The Late Carboniferous whip spider Graeophonus anglicus Pocock, 1911 (Arachnida: Amblypygi), is redescribed on the basis of the holotype and nine other specimens all preserved in sideritic nodules from the British Middle Coal Measures of Coseley, Staffordshire, UK. This species is clearly basal with respect to most living whip spiders, expressing numerous plesiomorphic character states and can be referred to both the suborder Paleoamblypygi and the ‘living fossil’ family Paracharontidae (with one Recent species), the latter based on an explict character of dorsal spination on the pedipalp femur. This suggests that crown-group Amblypygi originated by at least the mid-Palaeozoic.

A new chasmataspid (Chelicerata: Chasmataspidida) is described from the Early Silurian (Late Llandovery–Early Wenlock) of Lesmahagow, Scotland, as Loganamaraspis dunlopi gen. et sp. nov. It is distinguished from related forms by the low tapering ratio of the postabdomen, pediform sixth prosomal appendage and a heart-shaped metastoma. Additionally, a genital operculum with a genital appendage is preserved. The recognisable morphology of L. dunlopi gen. et sp. nov. bridges some of the gap between the Ordovician Chasmataspididae and the Devonian Diploaspididae. Traces of the gut are reported for the first time from a chasmataspid. Chasmataspids are regarded as sister group to the eurypterids: an anterior opercular plate anterior to the genital appendage in L. dunlopi gen. et sp. nov. is regarded as homologous to the anterior opercular plate of the three-segmented genital operculae of Dolichopterus and Stylonurina. This is considered a plesiomorphic character within Eurypterida, whilst the two-segmented genital operculum (with deltoid plates) of Eurypterina is considered apomorphic.

The type material of Chasmataspis laurencii Caster & Brooks, 1956 (Chelicerata: Chasmataspidida) from the Middle Ordovician (Tremadoc to Caradoc) of Sevier County, Tennessee, USA, is redescribed, and comparisons are drawn with recently discovered Devonian chasmataspids from Scotland, Germany and Russia. The depositional setting of the C. laurencii fossils is reinterpreted as an ash fall into shallow marine/tidal sediments. Chasmataspis laurencii confirms the presence of 13 opisthosomal segments in Chasmataspidida, a character of unresolved polarity. The phylogenetic position ofC. laurencii is difficult to resolve. A monophyletic Chasmataspidida has one convincing autapomorphy in the nine-segmented postabdomen, but C. laurencii shares a number of characters with xiphosurans (i.e. cardiac lobe, pre-abdomen with axial region, biramous and chelate limbs), while the Devonian taxa more closely resemble eurypterids (i.e. through pediform limbs and a genital appendage). Earlier interpretations of the respiratory system in C. laurencii appear unconvincing in the light of new evidence from Devonian forms with opisthosomal opercula. Resting impressions of a Chasmataspis-like animal from the Upper Cambrian Hickory Sandstone of Texas, USA, also appear to show evidence of opercula. These Texan fossils could represent the oldest record of Euchelicerata. Two chasmataspid families are recognised, and C. laurencii is placed in the monotypic Chasmataspididae Caster & Brooks, 1956, redefined here on the fused pre-abdominal buckler with an axial region and the narrow, elongate post-abdomen ending in a long, lanceolate telson.

Study of abundant phalangiotarbid (Arachnida: Phalangiotarbida) material – provisionally assigned here to Bornatarbus mayasii (Haupt in Nindel 1955) – from the Upper Carboniferous of Writhlington, UK, has revealed new information about some previously equivocal characters. The present authors report a trifurcate apotele, possible spiracles on sternite 5, and confirm the presence of 10 opisthosomal tergites plus a dorsal anal operculum. The affinities of phalangiotarbids are obscure, with most authors favouring affinities with Opiliones (harvestmen) and/or Acari (mites and ticks). Phalangiotarbida is scored for characters used in previous studies of arachnid relationships. A cladistic analysis based on 63 characters using 13 terminal arachnid taxa (plus a hypothetical outgroup), resolves Phalangiotarbida as sister group to (Palpigradi + Tetrapulmonata): the taxon Megoperculata sensu Shultz (1990). Even under cladistic analysis, the position of the Phalangiotarbida remains hard to resolve, but a prosomal sternite with distinct sclerites potentially groups them with the Megoperculata.

A new hypothesis of the relationships between arachnomorph arthropods, and the origin of chelicerates, is presented based on a cladistic analysis of 34 taxa and 54 characters. The present study provides a detailed discussion of primary hypotheses of homology and includes a more complete range of terminal taxa than previous analyses. The analysis provides the first convincing synapomorphies for the Arachnomorpha, and suggests that the marrellomorphs are not arachnomorphs. The assignment of Cambrian ‘great appendage’ (or megacheiran) arthropods to the Arachnomorpha is confirmed, and potential synapomorphies uniting them with chelicerates are discussed and tested. Principal amongst these are the loss of the first cephalic appendages (the antennae), loss of the exopods of the second cephalic appendages and modification of the endopods of these appendages into spinose grasping organs. The Arachnomorpha consists of two major clades: (1) a ‘chelicerate-allied’ clade, including chelicerates, megacheirans, Emeraldella, Sidneyia, cheloniellids and aglaspidids, in which chelicerates and a paraphyletic group of megacherian arthropods form the sister group to the remaining taxa; and; (2) a ‘trilobite-allied’ clade, including trilobites, xandarellids, helmetiids, tegopeltids and naraoiids, the relationships of which are more fully resolved than in previous studies.

A new chasmataspid (Chelicerata, Chasmataspida) is described as Forfarella mitchelli gen. et sp. nov. from the Lower Devonian of Scotland. This species is problematic in that it was catalogued under the name Forfarella mitchelli Waterston (no date), but was never formally described. Furthermore, its type locality is uncertain. Chasmataspids are a poorly known taxon within Chelicerata which appear to be closely related to eurypterids. F. mitchelli is only the fourth chasmataspid species to be described. Though poorly preserved, it shows affinities with other Devonian chasmataspids and supports the hypothesis that this group may have been more geographically widespread in the Devonian than has previously been recognised.