Prosomal Appendages Research Articles

Pedipalp anatomy of the Australian black rock scorpion, Urodacus manicatus, with implications for functional morphology

Pedipalps – chelate ‘pincers’ as the second pair of prosomal appendages – are a striking feature of scorpions and are employed in varied biological functions. Despite the distinctive morphology and ecological importance of these appendages, their anatomy remains underexplored. To rectify this, we examined the pedipalps of the Australian black rock scorpion, Urodacus manicatus, using a multifaceted approach consisting of microcomputed tomography, scanning electron microscopy, energy dispersive X-ray spectroscopy, and live pinch force measurements. In doing so, we document the following aspects of the pedipalps: (1) the musculature in three dimensions; (2) the cuticular microstructure, focusing on the chelae (tibial and tarsal podomeres); (3) the elemental construction of the chelae teeth; and (4) the chelae pinch force. We recognise 25 muscle groups in U. manicatus pedipalps, substantially more than previously documented in scorpions. The cuticular microstructure – endo-, meso-, and exocuticle – of U. manicatus pedipalps is shown to be similar to other scorpions and that mesocuticle reinforces the chelae for predation and burrowing. Elemental mapping of the chelae teeth highlights enrichment in calcium, chlorine, nickel, phosphorus, potassium, sodium, vanadium, and zinc, with a marked lack of carbon. These elements reinforce the teeth, increasing robustness to better enable prey capture and incapacitation. Finally, the pinch force data demonstrate that U. manicatus can exert high pinch forces (4.1 N), further highlighting the application of chelae in subduing prey, as opposed to holding prey for envenomation. We demonstrate that U. manicatus has an array of adaptions for functioning as a sit-and-wait predator that primarily uses highly reinforced chelae to process prey.

Lower Ordovician synziphosurine reveals early euchelicerate diversity and evolution

Euchelicerata is a clade of arthropods comprising horseshoe crabs, scorpions, spiders, mites and ticks, as well as the extinct eurypterids (sea scorpions) and chasmataspidids. The understanding of the ground plans and relationships between these crown-group euchelicerates has benefited from the discovery of numerous fossils. However, little is known regarding the origin and early evolution of the euchelicerate body plan because the relationships between their Cambrian sister taxa and synziphosurines, a group of Silurian to Carboniferous stem euchelicerates with chelicerae and an unfused opisthosoma, remain poorly understood owing to the scarce fossil record of appendages. Here we describe a synziphosurine from the Lower Ordovician (ca. 478 Ma) Fezouata Shale of Morocco. This species possesses five biramous appendages with stenopodous exopods bearing setae in the prosoma and a fully expressed first tergite in the opisthosoma illuminating the ancestral anatomy of the group. Phylogenetic analyses recover this fossil as a member of the stem euchelicerate family Offacolidae, which is characterized by biramous prosomal appendages. Moreover, it also shares anatomical features with the Cambrian euarthropod Habelia optata, filling the anatomical gap between euchelicerates and Cambrian stem taxa, while also contributing to our understanding of the evolution of euchelicerate uniramous prosomal appendages and tagmosis.

The "elongate chelicera problem": A virtual approach in an extinct pterygotid sea scorpion from a 3D kinematic point of view.

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.

The first documentation of an Ordovician eurypterid (Chelicerata) from China

AbstractAn 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.UUID: http://zoobank.org/a2d090e5-1a15-40b6-8e2a-dda45b01e94d

Identification and Morphology of the Two Horseshoe Crab Species, Tachypleus tridentatus (Leah, 1819) and Carcinoscorpius rotundicauda (Latreille, 1802) (Merostomata: Limulidae) from Honda Bay, Palawan, Philippines

There were reports of the existence of horseshoe crabs in Palawan, Philippines, but there is a need to identify and confirm these species. A total of 128 adult horseshoe crabs were collected from Honda Bay, Palawan, Philippines. These were identified as Tachypleus tridentatus (68 males, 40 females) and Carcinoscorpius rotundicauda (2 males, 18 females). Morphology, morphometric measurements, and ratios of male and female of each species were described. Morphological characteristics in differentiating a male from a female crab involve examination of the appearance of the genitalia. Morphological characteristics in identifying the species include the presence or absence of notches in the frontal margin, arching in the frontal view, appearance of the chelae of the 2nd and 3rd prosomal appendages, number of lateral spines and the immovable spines in the opisthosoma, the presence of spinnerets on the surface of the telson, and shape of the telson and its cavity in cross-section. This study confirmed the identification of the two species found in Palawan, Philippines, and the morphological characteristics of the male and female of each species. In addition, a comparison was made of the size of the horseshoe crab species in Palawan with those found in other locations in the Asia-Pacific region.

The Chelicerae of Slimonia (Eurypterida; Pterygotoidea)

Pterygotid eurypterids are the most speciose eurypterid clade, accounting for almost a fifth of the approximately 250 known species, although it is unclear whether this increase in diversity is due to their increased dispersal ability, shift in predation style to cheliceral-driven prey capture, or some other factor. Determining if the development of their characteristic large chelicerae represents a key trait facilitating increased diversification is hindered by uncertainty regarding the form of the chelicerae in Slimonia, the sister taxon to Pterygotidae. Here I report the discovery of a specimen of Slimonia acuminata preserving the chelicerae in detail and corroborate reports from the 1800s suggesting that the chelicerae of Slimonia were short and robust. The evidence from the new specimen, taken in concert with the morphology of the rest of the animal, indicates that Slimonia was an active predator that captured prey with its robust prosomal appendages. The apparent increase in pterygotid species diversity therefore does indeed seem to be associated with the development of the large chelicerae; however, further work is needed to determine whether taphonomic biases in preservation due to increased sclerotization of the chelicerae or taxonomic oversplitting due to minor changes in denticle morphology are driving this phenomenon.

It takes Two: Discovery of Spider Pax2 Duplicates Indicates Prominent Role in Chelicerate Central Nervous System, Eye, as Well as External Sense Organ Precursor Formation and Diversification After Neo- and Subfunctionalization

Paired box genes are conserved across animals and encode transcription factors playing key roles in development, especially neurogenesis.Pax6is a chief example for functional conservation required for eye development in most bilaterian lineages except chelicerates.Pax6is ancestrally linked and was shown to have interchangeable functions withPax2.Drosophila melanogaster Pax2plays an important role in the development of sensory hairs across the whole body. In addition, it is required for the differentiation of compound eyes, making it a prime candidate to study the genetic basis of arthropod sense organ development and diversification, as well as the role of Pax genes in eye development. Interestingly, in previous studies identification of cheliceratePax2was either neglected or failed. Here we report the expression of twoPax2orthologs in the common house spiderParasteatoda tepidariorum, a model organism for chelicerate development. The twoPax2orthologs most likely arose as a consequence of a whole genome duplication in the last common ancestor of spiders and scorpions.Pax2.1is expressed in the peripheral nervous system, including developing lateral eyes and external sensilla, as well as the ventral neuroectoderm ofP. tepidariorumembryos. This not only hints at a conserved dual role ofPax2/5/8orthologs in arthropod sense organ development but suggests that in chelicerates,Pax2could have acquired the role usually played byPax6. For the other paralog,Pt-Pax2.2, expression was detected in the brain, but not in the lateral eyes and the expression pattern associated with sensory hairs differs in timing, pattern, and strength. To achieve a broader phylogenetic sampling, we also studied the expression of bothPax2genes in the haplogyne cellar spiderPholcus phalangioides. We found that the expression difference between paralogs is even more extreme in this species, sincePp-Pax2.2shows an interesting expression pattern in the ventral neuroectoderm while the expression in the prosomal appendages is strictly mesodermal. This expression divergence indicates both sub- and neofunctionalization afterPax2duplication in spiders and thus presents an opportunity to study the evolution of functional divergence after gene duplication and its impact on sense organ diversification.

Spines and baskets in apex predatory sea scorpions uncover unique feeding strategies using 3D-kinematics

SummaryMegalograptidae and Mixopteridae with elongate, spinose prosomal appendages are unique early Palaeozoic sea scorpions (Eurypterida). These features were presumably used for hunting, an untested hypothesis. Here, we present 3D model-based kinematic range of motion (ROM) analyses of Megalograptus ohioensis and Mixopterus kiaeri and compare these to modern analogs. This comparison confirms that the eurypterid appendages were likely raptorial, used in grabbing and holding prey for consumption. The Megalograptus ohioensis model illustrates notable Appendage III flexibility, indicating hypertrophied spines on Appendage III may have held prey, while Appendage II likely ripped immobilized prey. Mixopterus kiaeri, conversely, constructed a capture basket with Appendage III, and impaled prey with Appendage II elongated spines. Thus, megalograptid and mixopterid frontalmost appendages constructed a double basket system prior to moving dismembered prey to the chelicerae. Such 3D kinematic modeling presents a more complete understanding of these peculiar euchelicerates and highlights their possible position within past ecosystems.

Three-dimensional kinematics of euchelicerate limbs uncover functional specialization in eurypterid appendages

AbstractSea scorpions (Euchelicerata: Eurypterida) explored extreme limits of the aquatic euchelicerate body plan, such that the group contains the largest known marine euarthropods. Inferences on eurypterid life modes, in particular walking and eating, are commonly made by comparing the group with horseshoe crabs (Euchelicerata: Xiphosura). However, no models have been presented to test these hypotheses. Here, we reconstruct prosomal appendages of two exceptionally well-preserved eurypterids, Eurypterus tetragonophthalmus and Pentecopterus decorahensis, and model the flexure and extension of these appendages kinematically in three dimensions (3D). We compare these models with 3D kinematic models of Limulus polyphemus prosomal appendages. This comparison highlights that the examined eurypterid prosomal appendages could not have moved prey items effectively to the gnathal edges and would therefore not have emulated the motion of an L. polyphemus walking leg. It seems that these eurypterid appendages were used primarily to walk or grab prey, and other appendages would have moved prey for mastication. Such 3D kinematic modelling highlights how eurypterid appendage morphologies placed substantial limits on their function, suggesting a high degree of specialization, especially when compared with horseshoe crabs. Such three-dimensional kinematic modelling of these extinct groups therefore presents an innovative approach to understanding the position of these animals within their respective palaeoecosystems.

New trace fossil evidence for eurypterid swimming behaviour

AbstractWe describe a recently discovered trace fossil from a eurypterid Konservat‐Lagerstätte in the upper Silurian Tonoloway Formation of Pennsylvania, and formally describe contemporaneous traces from the Williamsville Formation Lagerstätte of Ontario. The traces from both localities are assigned here to Arcuites bertiensis igen. et isp. nov. Based on comparisons with previously described eurypterid trackways, neoichnological experiments, and the co‐occurrence with eurypterid remains, Arcuites is interpreted as having been made by the swimming leg (sixth prosomal appendage) of swimming juvenile to adult eurypteroid eurypterids, and represents the first unambiguous trace fossil evidence for eurypterid swimming behaviour. The morphology of Arcuites indicates that eurypteroid eurypterids swam using drag‐based rowing, whereby the animal propelled itself forward by moving its oar blade‐like swimming paddles in an in‐phase backstroke. Arcuites morphology also indicates that the eurypteroid swimming appendage had a greater degree of movement than was previously suggested, and a revised rowing model is proposed. Differences in the abundance of A. bertiensis in the Tonoloway and Williamsville formations suggest a bathymetric control on eurypterid swimming behaviour and trace production. The association of Arcuites with eurypterid body fossils in both units indicates that these Lagerstätten were autochthonous assemblages and provides additional evidence for eurypterid inhabitation of shallow subtidal marine environments in the late Silurian.

Rapid diversification of homothorax expression patterns after gene duplication in spiders

BackgroundGene duplications provide genetic material for the evolution of new morphological and physiological features. One copy can preserve the original gene functions while the second copy may evolve new functions (neofunctionalisation). Gene duplications may thus provide new genes involved in evolutionary novelties.ResultsWe have studied the duplicated homeobox gene homothorax (hth) in the spider species Parasteatoda tepidariorum and Pholcus phalangioides and have compared these data with previously published data from additional spider species. We show that the expression pattern of hth1 is highly conserved among spiders, consistent with the notion that this gene copy preserves the original hth functions. By contrast, hth2 has a markedly different expression profile especially in the prosomal appendages. The pattern in the pedipalps and legs consists of several segmental rings, suggesting a possible role of hth2 in limb joint development. Intriguingly, however, the hth2 pattern is much less conserved between the species than hth1 and shows a species specific pattern in each species investigated so far.ConclusionsWe hypothesise that the hth2 gene has gained a new patterning function after gene duplication, but has then undergone a second phase of diversification of its new role in the spider clade. The evolution of hth2 may thus provide an interesting example for a duplicated gene that has not only contributed to genetic diversity through neofunctionalisation, but beyond that has been able to escape evolutionary conservation after neofunctionalisation thus forming the basis for further genetic diversification.

Note on the morphology and systematic position of Alkenopterus burglahrensis (Chelicerata: Eurypterida: Eurypterina) from the Lower Devonian of Germany

The holotype of the eurypterid Alkenopterus burglahrensis from the Lower Devonian (Siegenian) of the Westerwald area (Rhineland-Palatinate, SW Germany) is re-examined. In contrast to a previous concept, this species has flattened distal podomeres seven and eight and a movable flattened spine on the seventh podomere of the sixth prosomal appendage (podomere VI-7a). Based on the presence of such a slender paddle, A. burglahrensis has to be regarded as a basal ‘swimming eurypterid’ (Eurypterina) and is formally transferred here to the family Onychopterellidae, extending the stratigraphical range of this family into the Lower Devonian.

Babes in the wood--a unique window into sea scorpion ontogeny.

BackgroundFew 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.ResultsThe 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.ConclusionsThe 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 sejugal furrow in camel spiders and acariform mites

Camel spiders (Arachnida: Solifugae) are one of the arachnid groups characterised by a prosomal dorsal shield composed of three distinct elements: the pro-, meso- and metapeltidium. These are associated respectively with prosomal appendages one to four, five, and six. What is less well known, although noted in the historical literature, is that the coxae of the 4 th and 5 th prosomal segments (i.e. walking legs 2 and 3) of camel spiders are also separated ventrally by a distinct membranous region, which is absent between the coxae of the other legs. We suggest that this essentially ventral division of the prosoma specifically between coxae 2 and 3 is homolo - gous with the so-called sejugal furrow (the sejugal interval sensu van der Hammen). This division constitutes a fundamental part of the body plan in acariform mites (Arachnida: Acariformes). If homologous, this sejugal furrow could represent a further potential synapomorphy for (Solifugae + Acariformes); a relationship with increasing morphological and molecular support. Alternatively, outgroup comparison with sea spiders (Pycnogonida) and certain early Palaeozoic fossils could imply that the sejugal furrow defines an older tagma, derived from a more basal grade of organisation. In this scenario the (still) divided prosoma of acariform mites and camel spiders would be plesiomorphic. This interpretation challenges the textbook arachnid character of a peltidium (or 'carapace') covering an undivided prosoma.

The hemolymph vascular system in Cupiennius salei (Araneae: Ctenidae)

In terms of physiology and behavior, Cupiennius salei is one of the best-investigated spider species. However, parts of its anatomy have only been described superficially to date. In the course of a comparative survey of the hemolymph vascular system in Araneae we therefore investigated C. salei using several injection methods in combination with semi-thin sections and micro computer tomography (MicroCT). Like all other Arthropoda, C. salei possesses an open circulatory system. A tubular heart is suspended dorsally in the opisthosoma via a number of ligaments. It is equipped with three pairs of ostia, and three pairs of cardiac arteries. The heart is surrounded by a pericardial sinus in which we were able for the first time to describe an intra-pericardial membrane. Anteriorly, the heart is extended by an anterior aorta which runs through the pedicel and divides into two branches within the prosoma. Arteries emanating from the branches of the aorta supply the prosomal appendages and the central nervous system. The subesophageal ganglion is supplied by numerous fine vessels which emanate from the transganglionic arteries and form tight loops. A network of capillaries, i.e. interconnections between afferent and efferent vessels, is here demonstrated for the first time to exist in the central nervous system of chelicerates. Data are compared with existing literature on the morphology of the circulatory system in Araneae and discussed with regard to the extension of the respiratory system and the varying lifestyles of different spiders.

Redescription ofDrepanopterus pentlandicusLaurie, 1892, the earliest known mycteropoid (Chelicerata: Eurypterida) from the early Silurian (Llandovery) of the Pentland Hills, Scotland

ABSTRACTDrepanopterus pentlandicusLaurie, 1892 is redescribed from the original type material along with previously unfigured specimens. A cleft metastoma is confirmed as a characteristic of the genus, along with the armature of the second and third prosomal appendages being modified into flattened blades, while the species is shown to possess a somewhat enlarged second tergite and lateral prosomal margins that overlap the first opisthosomal tergite. Different ontogenetic stages ofD. pentlandicusare described, and reveal that these latter characters develop only later in ontogeny, suggesting that described specimens ofDrepanopterus abonensisSimpson, 1951 may represent juveniles. Cladistic analysis of Stylonurina shows the genusDrepanopterusto be monophyletic consisting ofD. pentlandicus,D. abonensisandD. odontospathussp. nov.: it forms a basal clade of mycteropoids. Hibbertopteroidea Kjellesvig-Waering, 1959 is shown to be a junior subjective synonym of Mycteropoidea Cope, 1886, with the synonymy of many of the hibbertopterid genera hypothesised andHibbertopterusKjellesvig-Waering, 1959 suggested to represent juvenile specimens ofCyrtoctenusStørmer & Waterston, 1968.Hibbertopterus permianusPonomarenko, 1985 is transferred toCampylocephalusEichwald, 1860. The role of heterochrony in the morphological development of the mycteropoid lineage is discussed, with both hibbertopterids and mycteropids suggested to be hypertrophic and pre-displacement peramorphs respectively.

The systematics and phylogeny of the Stylonurina (Arthropoda: Chelicerata: Eurypterida)

The first well-resolved phylogeny of stylonurine eurypterids (30 taxa, 58 characters) is presented, prompting a taxonomic revision at the familial and superfamilial levels. The monophyletic suborder Stylonurina consists of four superfamilies: Rhenopteroidea, Stylonuroidea, Kokomopteroidea and Hibbertopteroidea. The enigmatic hibbertopterids – large sweep-feeding forms from the Carboniferous to end-Permian – are therefore demonstrated to be an in-group Stylonurina clade, within Eurypterida, in contrast to some earlier hypotheses. Furthermore, the genus Drepanopterus is shown to be polyphyletic: ‘Drepanopterus’ bembycoides is transferred to Moselopteridae fam. nov. along with Moselopterus and Vinetopterus at the base of the Eurypterina, defined by their possession of a pediform appendage VI bearing a modified podomere 7a. Evolution towards a sweep-feeding mode of life occurred independently in stylonuroids and hibbertopteroids, involving either multiple rows of fixed spines on the prosomal appendages (in stylonuroids) or paired movable flattened spines (‘blades’) on the prosomal appendages alongside a posteriorly cleft metastoma and coxal laden (in hibbertopteroids). The Stylonurina have a relatively poor fossil record (RCI 15%), when compared to more derived Eurypterina clades (e.g. Adelophthalmoidea RCI 66%; Pterygotoidea RCI 53%), but is relatively more complete than basal Eurypterina clades (RCI -21%). The fit between phylogeny and stratigraphical occurrences of stylonurid taxa is good (SCI 0.65 and GER 0.77, with only 0.3% of 1000 randomisation tests yielding greater congruence; GER* 0.995), and generic-level collector curves of the Stylonurina and Eurypterina show no major discrepancies in their sampling histories. These differences could be explained by geographic collection bias, taxa having different habitat preferences (and hence fossilisation potential), and ontogenetic factors: these results support previous suggestions that stylonurine eurypterids are oversplit.

Like father, like son? Not amongst the eurypterids (Chelicerata) from Beartooth Butte, Wyoming

The eurypteridStrobilopterus princetoniifrom the Lower Devonian Beartooth Butte Formation of Wyoming is redescribed, and previously unknown morphological features, including shape and position of eyes and ocelli are identified, and the prosomal appendages are described in more detail. The monotypicErieopterus latus, based on a much smaller specimen from the same locality, shares a large number of characters withS. princetonii, and must be interpreted as belonging to the genusStrobilopterus.It is here interpreted as a juvenileS. princetonii, but exhibits extreme ontogenetic variation in the morphology of the swimming leg. The other monotypic eurypterid from the locality,Dorfopterus angusticollis, remains mysterious. It might be aS. princetoniitelson, but evidence is inconclusive. The name of the Devonian eurypterid genusSyntomopterusis preoccupied for a beetle (Coleoptera: Insecta) and the replacement nameSyntomopterellais proposed. The phylogenetic position ofS. princetoniiis problematic since it lacks unequivocal synapomorphies with other eurypterids, but the genus is showing more similarities toSyntomopterella, ErieopterusandBuffalopterusthan it does toDolichopterus, contrary to earlier suggestions.

Kiaeropterus (Eurypterida; Stylonurina) recognized from the Silurian of the Pentland Hills

Synopsis Eurypterus cyclophthalmus Laurie, 1892 from the Llandovery of the Pentland Hills, Scotland, is redescribed and assigned to the stylonurid eurypterid genus Kiaeropterus Waterston. 1979, previously only known from Kiaeropterus ruedemanni (Størmer, 1934) from the Wenlock of Norway. Another species previously assigned to Kiaeropterus, K. otisius Clarke 1907, is reassigned to the previously monotypic genus Clarkeipterus Kjellesvig-Waering 1966. The genus Kiaeropterus shares a previously unrecognized synapomorphy with the genus Brachyopterus Størmer 1951, namely a large bulbous ‘ocellar area’. In Kiaeropterus this area is cardioid whereas it is triangular in Brachyopterus. The two genera also share a number of less significant characters such as large anteriorly converging crescentic eyes, a lack of cuticular ornament and podomeres of the prosomal appendages with pronounced ridges, supporting a phylogenetic relationship between Kiaeropterus and Brachyopterus.

Eurypterida (Chelicerata) from the Welsh Borderlands, England

Eurypterids from the Welsh Borderlands of England are redescribed from most available material. Hughmilleria banksii is here interpreted to represent a new genus. The poorly known Hughmilleria (?) acuminata (Salter, 1859a) is considered a junior synonym of H. banksii. Furthermore, Slimonia? stylops is suspected to be a junior synonym of Salteropterus abbreviatus, although they are not formally synonymized as the location of the only known specimen of S.? stylops is unknown. Morphological differences in carapace shape, eye position, walking leg, genital appendage and telson in H. banksii are noted compared to previous descriptions. A prosomal appendage earlier assigned to H. banksii is here assigned with caution to S. abbreviatus and the reported ‘segments’ in the posterior part of the telson of S. abbreviatus are shown to be cracks. The phylogenetic position of the new genus is inferred to lie between the Hughmilleria and the Slimonia/Salteropterus clades.