Almost a spider: a 305-million-year-old fossil arachnid and spider origins

Spiders are an important animal group, with a long history. Details of their origins remain limited, with little knowledge of their stem group, and no insights into the sequence of character acquisition during spider evolution. We describe a new fossil arachnid, Idmonarachne brasieri gen. et sp. nov. from the Late Carboniferous (Stephanian, ca 305–299 Ma) of Montceau-les-Mines, France. It is three-dimensionally preserved within a siderite concretion, allowing both laboratory- and synchrotron-based phase-contrast computed tomography reconstruction. The latter is a first for siderite-hosted fossils and has allowed us to investigate fine anatomical details. Although distinctly spider-like in habitus, this remarkable fossil lacks a key diagnostic character of Araneae: spinnerets on the underside of the opisthosoma. It also lacks a flagelliform telson found in the recently recognized, spider-related, Devonian–Permian Uraraneida. Cladistic analysis resolves our new fossil as sister group to the spiders: the spider stem-group comprises the uraraneids and I. brasieri. While we are unable to demonstrate the presence of spigots in this fossil, the recovered phylogeny suggests the earliest character to evolve on the spider stem-group is the secretion of silk. This would have been followed by the loss of a flagelliform telson, and then the ability to spin silk using spinnerets. This last innovation defines the true spiders, significantly post-dates the origins of silk, and may be a key to the group''s success. The Montceau-les-Mines locality has previously yielded a mesothele spider (with spinnerets). Evidently, Late Palaeozoic spiders lived alongside Palaeozoic arachnid grades which approached the spider condition, but did not express the full suite of crown-group autapomorphies.     

The significance of relatedness and gene flow on population genetic structure in the subsocial spider Eresus cinnaberinus (Araneae: Eresidae)

Interdemic selection, inbreeding and highly structured populations have been invoked to explain the evolution of cooperative social behaviour in the otherwise solitary and cannibalistic spiders. The family Eresidae consists of species ranging from solitary and intermediate subsocial to species exhibiting fully cooperative social behaviour. In this study we, in a hierarchical analysis, investigated relatedness of putative family clusters, inbreeding and population genetic structure of the subsocial spider Eresus cinnaberinus. Five hierarchical levels of investigation ranging from large scale genetic structure (distances of 250 and 50 km level 1 and 2) over microgeographic structure (20 km² and 4 km², level 3 and 4) to a single hill transect of 200 m (level 5) were performed. The purpose of level 5 was two-fold: (1) to investigate the relatedness of putative family groups, and (2) to evaluate the influence of both family living and sampling design on higher level estimates. Relatedness estimates of putative family groups showed an average relatedness of R=0.26. There was no indication of inbreeding. In contrast to social spiders, genetic variation was abundant, H_e?0.10. The population genetic structure was intermediate between social and asocial spiders. Genetic variance increased continually across hierarchical levels. Family structured neighbourhoods biased differentiation estimates among level 5 samples (F_ST? 0.04) and level 3 and 4 samples (0.07ST<0.18), and apparent inbreeding among level 3 and 4 samples, F_IS>0, was caused by disjunct sampling from separate neighbourhoods. Larger scale samples were highly differentiated 0.12ST<0.26, depending on level and sampling design. Due to a distance effect family living did not influence estimates of the higher level 1. Although the dispersing sex among social spiders and the subsocial E. cinnebarinus differ, females versus males, female behaviour of both sociality classes lead to high genetic variance.     

SPIRACLE STRUCTURE IN TICKS (IXODIDA: ANACTINOTRICHIDA: ARACHNIDA): RÉSUMÉ, TAXONOMIC AND FUNCTIONAL SIGNIFICANCE

Spiracle and tracheal structure in the extant Ixodida is revised and shown to comprise 29 distinct component characters, some of which are common to all Anactinotrichida, while others are unique to the Ixodida or one of its six component clades of ((Argasidae Nuttalliellidae) (Prostriata Metastriata)). Structural variation both between and within families is based upon combinations of minor differences in the component characters, only one of which, spiracular position, proved to be incongruent within the most parsimonious cluster- and tree-analysis solutions. Tracheal airflow in ticks is mediated via passive diffusion gradients. In the argasid spiracle, both aeropyles and ostium are functional, although the latter is only opened briefly during infrequent periods of activity. The ixodid ostium is sealed and all gas exchange takes place via an enlarged sieveplate which reduces transpiration via small aeropyles, an underlying dense array of pedicels and possibly hygroscopic sub-atrial glands. Changes in spiracular morphology from a more ‘ancestral’ argasid type to a more ‘derived’ ixodid type are correlated with changes in tick behaviour, particularly with increased activity associated with the change from nidicoly to host-seeking.     

The first karyotype study in palpigrades, a primitive order of arachnids (Arachnida: Palpigradi)

Chromosomes of palpigrades (Arachnida: Palpigradi), a rare arachnid order with numerous primitive characters, were studied for the first time. We analysed two species of the genus Eukoenenia, namely E. spelaea and E. mirabilis. Their karyotypes are uniform, consisting of a low number of tiny chromosomes that decrease gradually in size. Study of the palpigrade karyotype did not reveal morphologically differentiated sex chromosomes. Analysis of E. spelaea showed that constitutive heterochromatin is scarce, GC-rich, and restricted mostly to presumed centromeric regions. Meiosis is remarkable for the presence of a short diffuse stage and prominent nucleolar activity. During prophase I, nuclei contain a large nucleolus. Prominent knob at the end of one bivalent formed by constitutive heterochromatin is associated to the nucleolus by an adjacent NOR. Presence of a nucleolus-like body at male prophase II suggests activity of NOR also during beginning of the second meiotic division. The data suggest acrocentric morphology of palpigrade chromosomes. Palpigrades do not display holocentric chromosomes which appear to be apomorphic features of a number of arachnid groups. These are: acariform mites, buthid scorpions, and spiders of the superfamily Dysderoidea. Therefore, cytogenetic data do not support a close relationship of palpigrades and acariform mites as suggested previously.     

Scorpions of the genus Odontobuthus Vachon, 1950 (Scorpiones: Buthidae) from Iran: Phylogenetic relationships inferred from mitochondrial DNA sequence data

The molecular phylogeny of the genus Odontobuthus Vachon, 1950 (Scorpiones: Buthidae) in Iran was evaluated using two mitochondrial DNA genes, cytochrome c oxidase, subunit I (COI) and 16S ribosomal RNA (16S rRNA). The molecular phylogenetic analyses were performed using Maximum Parsimony, Maximum Likelihood and Bayesian inference methods. The resulting topologies supported two main clades: the clade comprising Odontobuthus doriae, O. bidentatus, and O. tavighiae, and another one which is the O. tirgari clade. The results clearly presented additional support for the taxonomic validity of the recently described species, O. tirgari and O. tavighiae. In addition, the monophyly of two previously described species O. doriae and O. bidentatus was confirmed. According to the data presented here, three taxonomically valid species belonging to the genus Odontobuthus occur in Iran.     

中国甘肃拟蝇虎属一新种(蜘蛛目:跳蛛科)

记述甘肃跳蛛一新种：指状拟蝇虎Plexippoides digitatus sp.nov.。模式标本保存于中国科学院动物研究所,量度单位为mm。指状拟蝇虎Plexippoides digitatus sp.nov.（图1－4）正模♂,1998年7月14日,陈军采自甘肃康县清河林场,标本编号SP98040。鉴别特征新种与盘触拟蝇虎Plexippoides discifer(Schenkel,1953)相似,但有以下区别：1）新种的插入器起始于12点钟位置（图2）,而后者则起始于5点钟位置;2）生殖球的耳状突长,位于9点钟处（图2）,而后者则起如于12：30处;3）跗舟突出明显细长（图3－4）;4）后侧观（图3）肺节突明显大而短,端部宽、中央凹陷,而后者则为指纹。新种的种名取自胫节突的形状。     

Redescription of Paradiscocyrtus neglectus Mello-Leitão, 1927 (Opiliones: Gonyleptidae), with the designation of a neotype and two synonymies

Paradiscocyrtus neglectus Mello-Leitão, 1927 is here redescribed and for the first time illustrated. A neotype is proposed to clarify the taxonomic status of this species and to differentiate it from the other two species of Paradiscocyrtus and related genera (e.g., Discocyrtus). Two junior synonyms of this species, currently allocated in Discocyrtus Holmberg, 1876 are here detected. This harvestman is endemic from areas above 2000 meters of altitude, occurring in the Campos Rupestres montane savannas terrestrial eco-region in the states of Minas Gerais and Rio de Janeiro, Brazil. This species is characterized by the powerful retrodorsal apophysis of the coxa IV, the unique armature of dorsal scutum, trochanter IV, and femur IV.     

The role of bracket fungi in creating alpha diversity of invertebrates in the Białowieża National Park,Poland

Bracket fungi are seen mainly as the cause of economic losses in forestry, and their role as creators of biodiversity is relatively poorly understood. The aim of the study was defining the manner in which the degree of decay (DD) of the fruiting bodies determines the character of the invertebrate assemblages colonising them. The effect of this group of fungi on the modification of biodiversity of invertebrates (Aranae, Opiliones, Pseudoscorpionida, two groups of mites—Mesostigmata and Oribatida, and Collembola and Insecta) was investigated by analyzing 100 fruiting bodies of 10 species of bracket fungi divided into four DD classes. The material was collected at Białowieża National Park, which is considered to be the largest area of natural forests in the North European Plain. 16 068 invertebrate individuals classified into 224 species were obtained. Oribatid mites (12 543 individuals) constituted the largest group of individuals, which were classified into 115 species with the most numerous Carabodes femoralis (8,811 individuals). Representatives of this group of mites have been reported previously in the publications on bracket fungi; however, the contributions of Oribatida and other groups of invertebrates were not broadly compared. Moreover, the species such as Hoploseius mariae and H. oblongus, which were predominantly found in fruiting bodies of bracket fungi, have also been discerned. The invertebrate fauna differs depending on DD of the samples: In the more decayed samples, a higher number of both individuals and species were recorded compared to the samples with lower DDs; however, this trend proved to be nonlinear. The DCA and cluster analysis revealed a similarity of the invertebrate assemblages from the 2 DD and 4 DD samples. They also indicated that the group 3 DD differed the most from all the other samples. The indicator species analysis identified species characteristic to individual DDs: For group 1 DD, it was, for example, Hoploseius oblongus; for 2 DD—Orchesella bifasciata; and for 3 DD—Chernes cimicoides, while for 4 DD—Dinychus perforatus.     

A new species of Discocyrtanus from Mato Grosso,Brazil (Opiliones: Gonyleptidae) with a key to the species of the genus

Discocyrtanus canjinjim sp. n., belonging to the family Gonyleptidae Sundevall, 1833 is described based on nineteen specimens, eleven adult males and eight adult females, collected in the Vila Bela da Santíssima Trindade, in the State of Mato Grosso, Brazil. This new species represents an endemic component for the harvestmen fauna of Chiquitano Dry Forests terrestrial eco-region, being the most occidental point of distribution of the genus, notably found in the Cerrado and the Atlantic Forest. The new species is characterized by femur IV swollen with the same length of dorsal scutum, trochanter IV with prodorsal distal apophysis as a stout hook not bifurcated, and a unique form of genitalia in the genus. This paper also includes the first identification key to the species of the genus after its revalidation.