Chelal growth in pseudoscorpions

There is a linear relationship between the successive positions of named trichobothria on the pedipalpal chelae during the course of post-embryonic development of five British pseudoscorpions belonging to the family Neobisiidae. Growth constants calculated from the trichobothrial data are higher than those calculated for the chelal axis. This discrepancy is resolved in terms of a model, based on growing and non-growing regions, which is a good approximation to the data. The extent of these regions is calculated for all stages and differences between the species are noted. The assumptions implicit in the model, its realism and its predictive value are discussed.     

THE EXTERNAL MORPHOLOGY OF TWO PSEUDOSCORPIONS NEOBISIUM CARPENTERI AND NEOBISIUM MARITIMUM

All stages of Neobisium carpenteri and N. maritimum are described and compared. Details are given of the chaetal counts, measurements, ratios and morphological characters which can be used to distinguish the species. These are compared with the corresponding stages of N. muscorum (Gabbutt & Vachon, 1965). A study of the positions of the trichobothria, on the fingers of the chelae of the three species, during successive stages, indicates the approximate place at which the increments are added at the moults. The different positioning of these growth zones results in disparities in the disposition of the trichobothria in the adult condition. The importance of the relative positions of the trichobothria, as well as the stage at which certain trichobothria first appear, are discussed briefly in relation to the systematics of this order.     

Central nervous projection patterns of trichobothria and other cuticular sensilla in the wandering spider Cupiennius salei (Arachnida,Araneae)

Summary Central projections of mechano-and chemoreceptors on the legs and pedipalps of the wandering spider Cupiennius salei were traced by anterograde cobalt fills. The primary afferent fibres from trichobothria, tactile hairs, lyriform organs and contact chemoreceptive hairs enter the leg ganglia and pedipalpal ganglia ventrally. On their way through these ganglia there is very little arborization. The main areas of arborization are in the sensory longitudinal tracts in the suboesophageal nervous mass. The central projections of all mechano-and chemoreceptors examined show somatotopic organization. Sensilla located proximally on the legs are represented in dorsally located sensory longitudinal tracts, whereas those located on distal leg segments enter more ventral tracts. The afferent fibres of receptors of identifical modality on a specific segment of all legs and of the pedipalps overlap in the same tracts. No indication for a tonotopic arrangement of the trichobothrial afferences was found, which might have been associated with the mechanical frequency tuning of the trichobothria known from other experiments. The convergence of the projections of different types of receptors in the sensory longitudinal tracts is considered to be an anatomical basis for their functional interaction in behaviour. Both the convergence of the projections of receptors from the same segment of different legs and the somatotopy are connectivity patterns possibly associated with the orientation of the spiders towards mechanical or chemical cues.     

Cheliceral chelal design in free-living astigmatid mites

Cheliceral chelal design in free-living astigmatid mites (Arthropoda: Acari) is reviewed within a mechanical model. Trophic access (body size and cheliceral reach) and food morsel handling (chelal gape and estimated static adductive crushing force) are morphologically investigated. Forty-seven commonly occurring astigmatid mite species from 20 genera (covering the Acaridae, Aeroglyphidae, Carpoglyphidae, Chortoglyphidae, Glycyphagidae, Lardoglyphidae, Pyroglyphidae, Suidasiidae, and Winterschmidtiidae) are categorised into functional groups using heuristics. Conclusions are confirmed with statistical tests and multivariate morphometrics. Despite these saprophagous acarines in general being simple ‘shrunken/swollen’ versions of each other, clear statistical correlations in the specifics of their mechanical design (cheliceral and chelal scale and general shape) with the type of habitat and food consumed (their ‘biome’) are found. Using multivariate analyses, macro- and microsaprophagous subtypes are delineated. Relative ratios of sizes on their own are not highly informative of adaptive syndromes. Sympatric resource competition is examined. Evidence for a maximum doubling of approximate body volume within nominal taxa is detected but larger mites are not more ‘generalist’ feeding types. Two contrasting types of basic ‘Bauplan’ are found differing in general scale: (i) a large, chunk-crunching, ‘demolition’-feeding omnivore design (comprising 10 macrosaprophagous astigmatid species), and (ii) a small selective picking, squashing/slicing or fragmentary/‘plankton’ feeding design (which may indicate obligate fungivory/microbivory) comprising 20 microsaprophagous acarid-shaped species. Seventeen other species appear to be specialists. Eleven of these are either: small (interstitial/burrowing) omnivores—or a derived form designed for processing large hard food morsels (debris durophagy, typified by the pyroglyphid Dermatophagoides farinae), or a specialist sub-type of particular surface gleaning/scraping fragmentary feeding. Six possible other minor specialist gleaning/scraping fragmentary feeders types each comprising one to two species are described. Details of these astigmatid trophic-processing functional groups need field validation and more corroborative comparative enzymology. Chelal velocity ratio in itself is not highly predictive of habitat but with cheliceral aspect ratio (or chelal adductive force) is indicative of life-style. Herbivores and pest species are typified by a predicted large chelal adductive force. Pest species may be ‘shredders’ derived from protein-seeking necrophages. Carpoglyphus lactis typifies a mite with tweezer-like chelae of very feeble adductive force. It is suggested that possible zoophagy (hypocarnivory) is associated with low chelal adductive force together with a small or large gape depending upon the size of the nematode being consumed. Kuzinia laevis typifies an oophagous durophage. Functional form is correlated with taxonomic position within the Astigmata—pyroglyphids and glycyphagids being distinct from acarids. A synthesis with mesostigmatid and oribatid feeding types is offered together with clarification of terminologies. The chelal lyrifissure in the daintiest chelicerae of these astigmatids is located similar to where the action of the chelal moveable digit folds the cheliceral shaft in uropodoids, suggesting mechanical similarities of function. Acarid astigmatids are trophically structured like microphytophagous/fragmentary feeding oribatids. Some larger astigmatids (Aleuroglyphus ovatus, Kuzinia laevis, Tyroborus lini) approximate, and Neosuidasia sp. matches, the design of macrophytophagous oribatids. Most astigmatid species reviewed appear to be positioned with other oribatid secondary decomposers. Only Dermatophagoides microceras might be a primary decomposer approximating a lichenivorous oribatid (Austrachipteria sp.) in trophic form. Astigmatid differences are consilient with the morphological trend from micro- to macrophytophagy in oribatids. The key competency in these actinotrichid mites is a type of ‘gnathosomisation’ through increased chelal and cheliceral height (i.e., a shape change that adjusts the chelal input effort arm and input adductive force) unrestricted by the dorsal constraint of a mesostigmatid-like gnathotectum. A predictive nomogram for ecologists to use on field samples is included. Future work is proposed in detail.

     

Testing compatibility between molecular and morphological techniques for arthropod systematics: a minimally destructive DNA extraction method that preserves morphological integrity, and the effect of lactic acid on DNA quality

Three practical aspects related to the preservation and destruction of DNA and/or morphological characters of spiders were examined: potential morphological damage during non-destructive DNA extraction was assessed by counting trichobothria, a fragile sensorial feature found on spider legs; the effect on yield of non-destructive DNA extraction; and whether possible DNA degradation is caused by residues of lactic acid, which is used as a temporary mounting medium for the study of morphological structures in spiders and insects. Destructive extractions yielded higher amounts of DNA than non-destructive methods. However, non-destructive methods yielded usable amounts of DNA while leaving delicate trichobothria intact. Of the non-destructive extractions, a longer digestion period (36 h vs. 12) yielded higher amounts of DNA and did not damage trichobothria. Lactic acid did not induce short-term DNA degradation or inhibit PCR reactions, even at high concentrations. These results show compatibility between molecular and morphological requirements without compromising DNA quality or specimen integrity.     

The evolution of pedipalps and glandular hairs as predatory devices in harvestmen (Arachnida,Opiliones)

Pedipalps are the most versatile appendages of arachnids. They can be equipped with spines (Amblypygi), chelae (Scorpiones), or adhesive pads (Solifugae), all of which are modifications to grasp and handle fast‐moving prey. Harvestmen (Opiliones) show a high diversity of pedipalpal morphologies. Some are obviously related to prey capture, like the enlargement and heavy spination of Laniatores pedipalps. Many Dyspnoi, by contrast, exhibit thin, thread‐like pedipalps that are covered with complex glandular setae (clavate setae). These extrude viscoelastic glue that is used to immobilize prey items. Comparable setae (plumose setae) have previously been found in representatives of both Eupnoi and Dyspnoi, yet comprehensive data on their distribution are lacking. This study examined the distribution and ultrastructure of glandular setae in harvestmen and related them to pedipalpal morphology. Pedipalpal and setal characters were analysed in a phylogenetic framework. We found that glandular setae are synapomorphic for and widespread in the Palpatores clade (Eupnoi plus Dyspnoi). Their occurrence correlates with pedipalp morphology and feeding habit. Remnants of arthropod cuticular structures or secretions, frequently found attached to glandular setae, and behavioural observations, underlined the importance of the setae for capturing and securing prey. We hypothesize that glandular setae evolved as an adaptation to capture small and agile prey, which are hard to catch with a capture basket. Details of ultrastructure indicate that the setae are derived sensilla chaetica, with both a secretory and sensory function. Derived ultrastructural characters of the glandular setae, such as slit‐like channel openings and a globular arrangement of the microtrichia, may increase their effectiveness. The functional role of further pedipalpal modifications, such as apophyses, stalked and hyperbendable joints, and curved segments, as well as sexual dimorphism and ontogenetic polymorphism, are discussed. Some implications of the results obtained for the taxonomic treatment of Phalangiidae are also discussed. These results shed new light on the biology and evolutionary history of this fascinating group of arthropods.     

蜘蛛听毛的电镜观察

选用新蛛类的9种蜘蛛作为研究的对象，通过听毛的电镜观察探讨听毛在不同类群的差异。研究结果表明：管网蛛科的北京马蹄蛛的毛窝和听毛显然与中纺类，原蛛类和新蛛类中其他科的种类均不相同。拟壁钱科的居室拟壁钱（有筛器蜘蛛）和北国壁钱（无筛器蛛蛛）的毛窝和听毛的结构相差悬殊，很难看出亲缘上的关系，刺瓣似隙蛛和机敏漏斗蛛的毛窝差别大，无法表明它们之间近缘，园蛛科和肖蛸科种类的听毛窝和听毛数目表明两者之间近缘。     

Reinterpretation of Dracochela deprehendor (Arachnida: Pseudoscorpiones) as a stem‐group pseudoscorpion

Abstract: The middle Devonian (Givetian–Eifelian) pseudoscorpion Dracochela deprehendor Schawaller, Shear and Bonamo is redescribed from the type material and an additional palpal fragment. Dracochela differs from extant pseudoscorpions in having numerous spinules on the leg tarsi, the femur at least as long as the patella on the posterior legs, the stem of the arolia thick, most blades of the serrulae only weakly fused and in lacking a spinneret on the chelicera. The blades of the cheliceral rallum are shown to have been arranged in two rows, as in most Heterosphyronida. The cheliceral serrulae are compared with analogous structures in other arachnids (Notostigmata, Opiliones, Palpigradi, Schizomida and Scorpiones), and it is concluded that the panctenal state (all lamellae attached to finger) is plesiomorphic relative to the hemictenal state (apical lamellae raised), which has evolved independently in Heterosphyronida and Neobisioidea. The trichobothriotaxy of the chela of Dracochela is shown to be similar to that of the extant family Pseudotyrannochthoniidae. The growth of the chelal fingers followed the same pattern as that seen in modern pseudoscorpions, with most of the increase in length occurring at the base of the fingers. The family Dracochelidae Schawaller, Shear and Bonamo is treated as a plesion and assigned to the stem‐group of Pseudoscorpiones. The ordinal name Chelonethi Thorell is restricted to crown‐group pseudoscorpions, and the superordinal name Pseudoscorpiones Latreille is adopted for the total‐group (i.e. stem‐group plus Chelonethi).     

First molecular phylogeny of the major clades of Pseudoscorpiones (Arthropoda: Chelicerata)

The phylogenetic relationships of the major lineages of the arachnid order Pseudoscorpiones are investigated for the first time using molecular sequence data from two nuclear ribosomal genes and one mitochondrial protein-encoding gene. The data were analyzed using a dynamic homology approach with the new program POY v.4 under parsimony as the optimality criterion. The data show monophyly of Pseudoscorpiones as well as many of its superfamilies (Feaelloidea, Chthonioidea, Cheiridioidea and Sternophoroidea), but not for Neobisiodea or Garypoidea. Cheliferoidea was not monophyletic either due to the position of Neochelanops, which grouped with some garypoids. In all the analyses, Feaelloidea constituted the sister group to all other pseudoscorpions; Chthonioidea is the sister group to the remaining families, which constitute the group Iocheirata sensu Harvey--a clade including pseudoscorpions with venom glands within the pedipalpal fingers. This phylogenetic pattern suggests that venom glands evolved just once within this order of arachnids.     

Evidence for air movement signals in the agonistic behaviour of a nocturnal arachnid (order Amblypygi)

Many arthropods possess filiform hair sensilla (termed trichobothria in arachnids), which are extremely sensitive detectors of medium particle displacement. Electrophysiological evidence in some taxa suggests that these sensilla can detect air particle displacements resulting from intraspecific communication signals. However, it has not yet been shown for any species that the air particle displacements detected by the filiform hairs are themselves perceived as a 'signal' (i.e. that individuals make behavioural decisions based upon the responses of these organs to the displays of conspecifics). We investigate the agonistic behaviour of the whip spider Phrynus marginemaculatus and the role of its trichobothria in receiving agonistic signals. Whip spiders have extremely elongated 'antenniform' first legs, which they vibrate close to their opponents during agonistic interactions, inducing air movements that excite their opponents' trichobothria. We find that ablation of the trichobothria causes significant increases in: (I) contest duration, and (II) the probability of contest escalation past aggressive displays to physical fighting. Therefore, in the absence of air movement-sensitive sensilla, contest assessment is impaired. This suggests that whip spiders exploit true air movement signals during agonistic interactions, and that these are received by the trichobothria. Furthermore, these results indicate that, in whip spiders, such signals help mitigate the cost of agonistic interaction.     

On the threshold of dispersal: hitchhiking on a giant fly favours exaggerated male traits in a male‐dimorphic pseudoscorpion

The evolution of exaggerated male traits is frequently driven by competition between males to control resources critical for female survival and/or reproductive success. For flightless arthropods specializing on patchy habitats, dispersal agents may represent one such critical resource. The Neotropical pseudoscorpion, Semeiochernes armiger, disperses to new habitats by attaching to the giant timber fly, Pantophthalmus tabaninus, as it ecloses from pupal boreholes within decaying Ficus trees. In a study that combined field observations of mating with experimental removal of individuals from a large, pre‐dispersal population, our morphometric analyses revealed that S. armiger is among the most highly sexually dimorphic pseudoscorpions known, with males possessing unusual, triangular‐shaped pedipalpal chelae (hands) and a male‐specific, dimorphic chela peg that exhibits threshold trait expression. Several lines of evidence indicate that extreme sexual dimorphism in S. armiger results from male competition to monopolize pantophthalmid bores as strategic sites for inseminating females on the verge of dispersal. Sexually dimorphic pedipalpal characters were significantly larger in males located in and around pantophthalmid boreholes, compared with males collected at the periphery of the pantophthalmid emergence zone. Removal of pseudoscorpions resulted in a significant decline in pedipalpal size of males associated with pantophthalmid bores, followed by a rebound in size after collected individuals were returned to the tree. Most significantly, field observations of mating indicate that this competition translates into intense selection for exaggerated male traits, with all traits of the sexually dimorphic chelae exhibiting highly significant sexual selection differentials in males. © 2013 The Linnean Society of London     

Copulatory Mechanism in Holocnemus pluchei and Pholcus opilionoides,With Notes on Male Cheliceral Apophyses and Stridulatory Organs in Pholcidae (Araneae)

Huber, B. A. 1994. Copulatory mechanism in Holocnemus pluchei and Pholcus opilionoides, with notes on male cheliceral apophyses and stridulatory organs in Pholcidae (Araneae).—Acta Zoologica (Stockholm) 76: 291–300. The pholcid spiders Holocnemus pluchei (Scopoli, 1763) and Pholcus opilionoides (Schrank, 1781) are investigated with respect to functional morphology of their genital organs using freeze-fixation of spiders during copula in liquid nitrogen and subsequent preparation of histological serial sections of the copulatory organs in functional contact. Special attention is paid to the mode of male pedipalpal arrestation before copulation, which is achieved in two quite different ways: in Pholcus by contact of the lateral cheliceral apophysis with the pedipalpal trochanter-apophysis, in Holocnemus by locking the pedipalpal trochanter between chelicera and pedipalpal coxa. The condition in Pholcus is considered to be apomorphic and to present a synapomorphy of about a dozen genera for which the name “Pholcus-group” is proposed. The stridulatory apparatus of Holocnemus pluchei is described, its biological significance discussed and an overview of accounts on stridulation in Pholcidae given.     

A new high-elevation scorpion species of the genus Scorpiops Peters, 1861 (Scorpiones: Euscorpiidae: Scorpiopinae) from the Himalayas,India

A new high-elevation scorpion species of the genus Scorpiops is described from the Indian state of Himachal Pradesh. Scorpiops spitiensis sp. nov. is the second highest-elevation scorpion species in Asia and the first one from India occurring at elevations above 4200 m. The new species closely resembles Scorpiops petersii, but it can be distinguished from it based on a suit of characters, one of which is the presence of 16 trichobothria on the external aspect of the patella, which is unique to the new species.     

Agonistic signals received by an arthropod filiform hair allude to the prevalence of near-field sound communication

Arthropod filiform hairs respond to air particle movements and are among the most sensitive animal sensory organs. In many species, they are tuned to detect predators or prey and trigger escape or prey capture behaviours. Here we show for the first time that these hairs also receive intraspecific near-field sound signals in an arachnid. During agonistic encounters, whip spiders (Arachnida, Amblypygi) perform antenniform leg vibration (ALV) displays that have significantly longer duration in contest winners than losers. During an ALV display: (i) the vibrating antenniform leg of the displaying whip spider is positioned close to the trichobothria (filiform hairs) on its opponent's walking legs, (ii) the vibrating antenniform leg can excite these trichobothria via air movements and without direct contact, (iii) the antenniform leg of the displaying whip spider vibrates at a frequency that causes particularly strong, sustained excitation and little adaptation in the trichobothria, and (iv) the duration of an ALV display can be extracted from the response of a trichobothrium. Since filiform hairs are widespread among arthropods, communication via such hairs could be extremely prevalent.     

The release of attack and escape behavior by vibratory stimuli in a wandering spider (Cupiennim salei keys.)

Summary The wandering spiderCupiennius salei responds to vibration of the substrate either with predatory behavior (approach) or with a startle reaction or escape behavior (withdrawal) (Fig. 3). The effects of different parameters of the signal in releasing this behavior were studied by applying various artificial stimuli to a spider standing on a vibrating platform with one or more legs. Receptors sensitive to substrate vibration and the trichobothria, which respond to airborne vibration, together determine the response. Spiders without trichobothria: The type of response to vertical vibrations isfrequency-dependent (Fig. 4a), with predatory reactions predominant at low frequencies (3–4 Hz), and withdrawal reactions at high frequencies (350–460 Hz). Whereas approach is most likely to occur at an intermediate, frequency-dependentamplitude, the probability of withdrawal increases continuously with increasing amplitude (Fig. 6). With sine wave stimuli the lowest threshold amplitude for approach is 9 m peak-to-peak (550 Hz, range tested 1–550 Hz) whereas that for withdrawal is 17 m (800 Hz, range tested 1–800 Hz). The threshold for approach is lower by 6–8 dB whenband-limited noise is used, and the probability of an approach response increases as the bandwidth is expanded. The threshold curve for withdrawal, however, is the same in all cases (Fig. 4b and 5). The spider is capable of both frequency and amplitude discrimination.The metatarsal and pretarsal slit sense organs contribute to these responses as is shown by increased thresholds following their destruction (Fig- 7). Intact animals, with functional trichobothria as well as slit sense organs: They have lower thresholds for withdrawal (by ca. 10 dB; Fig. 9) and shorter reaction times than do spiders without trichobothria. Unlike animals without trichobothria the amplitude thresholds of intact animals to bandlimited noise are ca. 7.5 dB lower than those to sine wave stimuli. The approach threshold is the same as that of spiders without trichobothria. According to direct observation the trichobothria are deflected by airborne sound generated by the substrate motion; the deflection angle increases with both amplitude and frequency of substrate vibration (Fig. 10).There is acentral nervous interaction between the signals from the trichobothria and the slit sense organs with the following basic properties: when both of the two receptor systems receive either a prey-like stimulus or a stimulus eliciting withdrawal their effects add, but when the trichobothria receive stimuli unlike prey they inhibit the approach reaction that would otherwise be triggered by substrate vibration.