Skeletomuscular anatomy of the harvestman Leiobunum aldrichi (Weed, 1893) (Arachnida: Opiliones: Palpatores) and its evolutionary significance

Skeletal muscles of the North American harvestman Leiobunum aldrichi are exhaustively surveyed and compared with other chelicerates to clarify the evolutionary morphology and phylogenetic relationships of arachnids. Representatives of 104 muscle groups are described and illustrated, and their possible functions are proposed. Comparisons of the feeding apparatus of L. aldrichi with that of other opilions, especially Sim (Cyphophthalmi) and Acromares (Laniatores), and two scorpion genera ( Centruroides, Pandinus ) indicate that the pharyngeal apparatus in L. aldrichi is derived and that its ability to accommodate large food particles is a secondary rather than primitive condition. Comparisons reveal several possible synapomorphies between Opiliones and Scorpiones suggesting that these orders may be sister groups. Apparently unique synapomorphies include an extrinsic cheliceral muscle that arises from the carapace and inserts on the second cheliceral article (deutomerite); an epistome divided into distal and proximal parts by a transverse sulcus; pharyngeal dilator muscles supported by a peripharyngeal skeleton formed by one dorsomedial and two ventrolateral epistomal processes, the latter also with muscular attachments to the endosternite; a specialized preoral chamber (stomodieca) derived from extensions (coxapophyses) of the coxae of the pedipalp and first two leg pairs; internal processes associated with the coxapophyses that serve, in part, as an attachment for muscles operating the coxa-trochanter joints, and lateral endosternal suspensor muscles that insert on the arthrodial membrane between the leg coxae. These are the first observations providing explicit support for an Opiliones-Scorpiones clade.     

Muscular anatomy of the giant whipscorpion Mastigoproctus giganteus (Lucas) (Arachnida: Uropygi) and its evolutionary significance

Skeletal muscles in the whipscorpion Mastigoproctus giganteus are surveyed and compared with those of several other to clarify the evolutionary morphology and phylogenetic relationships of arachnids. Representatives from 90 muscle groups are described and illustrated, and their possible functions are proposed. Principal results of this analysis include new proposed homologies for the anterior opisthosomal appendages and sclerites in tetrapulmonate arachnids (that is, Trigonotarbida, Araneae, Amblypygi, Uropygi), the discovery that muscular attachments in arthropods can shift from the mesodermal endosternite to the ectodermal exoskeleton, a reconstruction of the evolutionary transformations associated with the apparent uncoupling of pharyngeal and locomotor complexes in the prosoma of Pedipalpi (that is, Amblypygi and Uropygi), and an expanded list of unique synapomorphies supporting the sister-group status of Amblypygi and Uropygi.     

Muscular anatomy of the millipede Phyllogonostreptus nigrolabiatus (Diplopoda: Spirostreptida) and its bearing on the millipede "thorax"

The muscular anatomy of the millipede Phyllogonostreptus nigrolabiatus (Newport, 1844) (Diplopoda; Spirostreptida; Harpagophoridae) is comprehensively surveyed. The musculature of the first three postcollum pleurotergites, the "thorax," and their associated appendages was found to be more complex than that of the postthoracic rings. It is hypothesized that the musculature of the postthoracic segments is derived relative to that of the thoracic segments, which retain primitively free sternites and are not diplosegments. This hypothesis is discussed relative to previous hypotheses positing that the anteriormost three leg-bearing rings in millipedes are diplosegments. The musculature of spirostreptid gonopods is described in detail for the first time. Comparison of the cephalic musculature is made with previously described musculature in Julida showing that, while many aspects of the musculature are conserved, there exist interordinal differences, documenting the potential utility of comparative anatomical studies for resolving millipede phylogeny.     

A phylogenetic analysis and taxonomic revision of ricefishes,Oryzias and relatives (Beloniformes,Adrianichthyidae)

Ricefishes, known best by the model organism, the medaka, Oryzias latipes Temminck & Schlegel, 1846, comprise the family Adrianichthyidae, which ranges broadly throughout fresh and brackish waters of Central, South and Southeast Asia and the Indo‐Malay‐Philippines Archipelago as far east as Timor. Twenty‐eight Recent species are recognized here in two monophyletic genera, Adrianichthys and Oryzias. Xenopoecilus and Horaichthys are placed in synonymy of Oryzias for the first time. Adrianichthys comprises four species from Lake Poso, Sulawesi, Indonesia. Oryzias comprises 24 species that live throughout the range of the family. A fossil genus and species, ?Lithopoecilus brouweri from the Miocene of central Sulawesi, is included tentatively in the Adrianichthyidae. Evidence for the sister group relationship of adrianichthyids and exocoetoids is reviewed briefly and that relationship corroborated. Monophyly of adrianichthyids is likewise strongly supported here. Species groups within Oryzias are diagnosed as monophyletic largely based on osteology, colour pattern and meristic variation. They correspond only in part to species groups previously recognized based on chromosome constitution. Miniature species do not comprise a monophyletic group; disjunct absolute size in close relatives has evolved repeatedly. Oryzias latipes is a member of a species complex that includes O. luzonensis, O. curvinotus and the miniatures O. sinensis and O. mekongensis. A new species, Oryzias bonneorum sp. nov. , is described from Lake Lindu, Sulawesi, Indonesia. Lectotypes are designated for Haplochilus celebensis Weber, 1894 and Haplochilus timorensis Weber & de Beaufort, 1922. No claim to original US Government works. Journal compilation © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 154 , 494–610.     

MYGALOMORPH SPIDERS (ARANEAE: DIPLURIDAE) FROM THE LOWER CRETACEOUS CRATO LAGERSTÄTTE, ARARIPE BASIN, NORTH-EAST BRAZIL

Abstract:  The first mygalomorph spiders from the Lower Cretaceous Crato Lagerstätte of Cearà Province, north-east Brazil, are described, from adult males and females, in two new genera and species: Cretadiplura ceara Selden, gen. et sp. nov. and Dinodiplura ambulacra Selden, gen. et sp. nov. They belong to the extant family Dipluridae, hitherto known as fossils only from Tertiary strata; thus this occurrence extends the family record by some 90 myr.     

Morphology of locomotor appendages in Arachnida: evolutionary trends and phylogenetic implications

The morphological diversity of locomotor appendages in Arachnida is surveyed lo reconstruct phylogenetic relationships and discover evolutionary trends in form and function. The appendicular skeleton and musculature of representatives from the ten living arachnid orders ate described, and a system of homology is proposed. Character polarities are established through comparison with an outgroup. Limulus polyphemus Xiphosura). Cladistic analysis suggests that Arachnida is monophyletic and that absence of extensor muscles is a primitive condition. Extensors are primitively absent in Araneae. Amblypygi, Uropygi, Palpigradi, Ricinulei and Acari. Most similarities in the appendages of these orders are symplesiomorphic so that phylogenetic relationships among the 'extensorless' groups cannot be resolved solely on the basis of appendicular characters. Extensor muscles appear to have evolved once, and their presence is considered a synapomorphic feature of Opiliones, Scorpiones, Pseudoscorpiones and Solifugae. Solifugae lack extensors, but a parsimonious interpretation of other characters indicates that this is a secondary, derived condition. The phylogenetic relationships among these four orders are clarified by modifications of the patellotibial joint. Cladistic analysis indicates that Opiliones may be the sister group of the other three orders and that Scorpiones is the sister group of Pseudoscorpiones and Solifugae. Conclusions concerning phylogenetic relationships and evolutionary morphology presented here differ substantially from those of earlier studies on the locomotor appendages of Arachnida.     

Morphology of locomotor appendages in Arachnida: evolutionary trends and phylogenetic implications

The morphological diversity of locomotor appendages in Arachnida is surveyed lo reconstruct phylogenetic relationships and discover evolutionary trends in form and function. The appendicular skeleton and musculature of representatives from the ten living arachnid orders ate described, and a system of homology is proposed. Character polarities are established through comparison with an outgroup. Limulus polyphemus Xiphosura). Cladistic analysis suggests that Arachnida is monophyletic and that absence of extensor muscles is a primitive condition. Extensors are primitively absent in Araneae. Amblypygi, Uropygi, Palpigradi, Ricinulei and Acari. Most similarities in the appendages of these orders are symplesiomorphic so that phylogenetic relationships among the ‘extensorless’ groups cannot be resolved solely on the basis of appendicular characters. Extensor muscles appear to have evolved once, and their presence is considered a synapomorphic feature of Opiliones, Scorpiones, Pseudoscorpiones and Solifugae. Solifugae lack extensors, but a parsimonious interpretation of other characters indicates that this is a secondary, derived condition. The phylogenetic relationships among these four orders are clarified by modifications of the patellotibial joint. Cladistic analysis indicates that Opiliones may be the sister group of the other three orders and that Scorpiones is the sister group of Pseudoscorpiones and Solifugae. Conclusions concerning phylogenetic relationships and evolutionary morphology presented here differ substantially from those of earlier studies on the locomotor appendages of Arachnida.     

The giant fiber system in the forelegs (whips) of the whip spider Heterophrynus elaphus Pocock (Arachnida: Amblypygi)

Summary The front legs of the whip spider H. elaphus are strongly modified to serve sensory functions. They contain several afferent nerve fibers which are so large that their action potentials can be recorded externally through the cuticle. In recordings from the tarsus 7 different types of afferent spikes were identified; 6 additional types of afferent spikes were discriminated in recordings from the tibia and femur. Most of the recorded potentials could be attributed to identifiable neurons serving different functions. These neurons include giant interneurons and giant fibers from diverse mechanoreceptors such as slit sense organs, trichobothria, and a joint receptor. In the present report these neurons are characterized using electrophysiological and histological methods. Their functions are discussed in the context of the animal's behavior.Abbreviations GN giant neuron - S segment     

The water-repellent cerotegument of whip-spiders (Arachnida: Amblypygi)

The cuticle of arthropods is usually composed of layers of a chitin-protein-microcomposite, a proteinaceous epicuticle and a thin lipid coating. However, in some instances a thick cement layer (cerotegument) covers the cuticle and may produce elaborate microstructures. This has previously been described for millipedes and mites. Here we report the previously unknown presence of a superhydrophobic cerotegument in whip-spiders (Ambypygi) and reveal its variation in ultrastructure and water-repellence between species. We discuss the relevance of found micro-morphological and physical characters for taxonomy and phylogenetics of this group, and the potential biological functions.     

Evolutionary morphology of whip spiders: towards a phylogenetic system (Chelicerata: Arachnida: Amblypygi)*

The aim of this study is to present a cladogram and phylogenetic system and to use this to discuss the phylogeny and biogeography of the Amblypygi. A total of 29 morphological structures were studied, their plesiomorphic and apomorphic characters or character states were identified, and the resulting data matrix was analysed. As a result, the ‘old’Charontidae or Pulvillata emerge as a paraphyletic group; the genus Paracharon is the sister group of all other amblypygids, which are now termed Euamblypygi. The ‘new’Charontidae (sensu Quintero: the genera Stygophrynus and Charon) are the sister group of the Phrynida or Apulvillata; together they form the Neoamblypygi. The relationships of the genera of the Charinidae cannot be resolved with the available data. They may be a paraphyletic group. The genus Catageus is a possible candidate for being the sister group of the Neoamblypygi. The new system allows a discussion of the phylogeny and biogeography of whip spiders. It also points to unresolved taxa and thus indicates the questions future research should address.     

Morphology and physiology of peripheral giant interneurons in the forelegs (whips) of the whip spider Heterophrynus elaphus Pocock (Arachnida: Amblypygi)

Summary The tarsi of the modified front legs (whips) of the whip spider Heterophrynus elaphus contain two afferent giant fibers, GN1 and GN2, with diameters at the tibia-tarsus joint of ca. 21 m and 14 m, respectively. The somata of these two neurons lie in the periphery, about 25 cm away from the CNS. These two neurons are interneurons which receive mechanoreceptive inputs from approximately 750 and 1500 bristles, respectively. The receptive fields of GN1 and GN2 overlap; they extend for 40 mm (GN1) and 90 mm (GN2) along the length of the tarsus. About 90% of the synapses onto the giant fibers are axo-axonic. Mechanical stimulation of a single bristle is sufficient to elicit action potentials in one or both interneurons. The response of the interneurons adapts quickly. Average conduction time from the soma to the CNS is 45 ms for GN1 and 55 ms for GN2. Mean conduction velocities are 5.5 and 4.2 m/s, respectively. Activity in the giant fibers does not elicit a motor response; hence the giant fibers do not mediate an escape response. Possible functions of these giant fibers are discussed and compared to those of giant fiber systems in other arthropods.Abbreviations GN giant neuron - S segment     

Wood anatomy of Penaeaceae (Myrtales): comparative, phylogenetic, and ecological implications

Wood samples of stems, lignotubers, and roots of the majority of species of Penaeaceae were analyzed with respect to qualitative and quantitative features. Virtually no data have hitherto been presented on xylem features of this family, restricted to Cape Province, South Africa. Presence of vestured pits in vessels, septate crystalliferous parenchyma in wood, intraxylary phloem, predominantly erect ray cells in the typically narrow, multiseriate rays and in the uniseriate rays, and amorphous deposits in ray cells place Penaeaceae securely in Myrtales and help to define that order. By comparison of ecological preferences of the species, as observed during field work, with quantitative analysis of conductive tissue, close correspondence of the wood structure to habit and habitat is demonstrated.     

Metabolic rate in the whip-spider, Damon annulatipes (Arachnida: Amblypygi)

Metabolic rate estimates as well as a measure of their repeatability and response to laboratory acclimation are provided for the amblypygid Damon annulatipes (Wood). This species (mean +/- S.E. mass: 640+/-66 mg) shows continuous gas exchange, as might be expected from its possession of book lungs, and at 21 degrees C has a metabolic rate of 30.22+/-2.87 microl CO2 h(-1) (approximately 229.6+/-21.8 microW, R.Q. = 0.72). The intraclass correlation coefficient (r=0.74-0.89) indicated substantial repeatability in metabolic rate which did not change with laboratory acclimation over a period of 2 weeks. By contrast, absolute metabolic rate declined by c. 16-33%, although this was not a consequence of changes in mass (which were non-significant over the same period). Rather, it appears that a reduction in overall stress or activity in the laboratory might have been responsible for the decline in mass-independent metabolic rate. At the intraspecific level, metabolic rate scaled as microW = 342 M(0.857), where mass is in grams. Metabolic rates of this species are in keeping with its sedentary behaviour such that for a given body size they are lower than those of most arthropods (spiders and insects), higher than the very sedentary ticks, and equivalent to scorpions. These findings have implications for the understanding of the evolution of metabolic rates in arthropods.     

Cladistics and the comparative morphology of linyphiid spiders and their relatives (Araneae, Araneoidea, Linyphiidae)

This paper provides the first quantitative cladistic analysis of linyphiid morphology. Classical and novel homology hypotheses for a variety of character systems (male and female genitalia, somatic morphology, spinneret silk spigot morphology, etc.) are critically examined and studied within a phylogenetic context. Critical characters have been illustrated. A sample of linyphiid taxa (nine genera in four subfamilies), five species of Pimoa (Pimoidae), and two other araneoid families (Tetragnathidae and Araneidae, represented by Tetragnatha and Zygiella , respectively) were used to study the implications of the phylogeny of Pimoidae for the systematics of linyphiids. The phylogenetic relationships of these 16 exemplar taxa, as coded for the 47 characters studied, were analysed using numerical cladistic methods. In the preferred cladogram Pimoidae and Linyphiidae are sister groups, Stemonyphantinae are sister group to the remaining linyphiids, and Mynogleninae are sister group to the clade composed of Erigoninae plus Linyphiinae. These results agree with the relationships recently proposed by Wunderlich, except by finding erigonines as the sister group to linyphiines rather than to mynoglenines.     

The gnathobasic spine microstructure of recent and Silurian chelicerates and the Cambrian artiopodan Sidneyia: Functional and evolutionary implications

Gnathobasic spines are located on the protopodal segments of the appendages of various euarthropod taxa, notably chelicerates. Although they are used to crush shells and masticate soft food items, the microstructure of these spines are relatively poorly known in both extant and extinct forms. Here we compare the gnathobasic spine microstructures of the Silurian eurypterid Eurypterus tetragonophthalmus from Estonia and the Cambrian artiopodan Sidneyiainexpectans from Canada with those of the Recent xiphosuran chelicerate Limulus polyphemus to infer potential variations in functional morphology through time. The thickened fibrous exocuticle in L. polyphemus spine tips enables effective prey mastication and shell crushing, while also reducing pressure on nerve endings that fill the spine cavities. The spine cuticle of E. tetragonophthalmus has a laminate structure and lacks the fibrous layers seen in L. polyphemus spines, suggesting that E. tetragonophthalmus may not have been capable of crushing thick shells, but a durophagous habit cannot be precluded. Conversely, the cuticle of S. inexpectans spines has a similar fibrous microstructure to L. polyphemus, suggesting that S. inexpectans was a competent shell crusher. This conclusion is consistent with specimens showing preserved gut contents containing various shelly fragments. The shape and arrangement of the gnathobasic spines is similar for both L. polyphemus and S. inexpectans, with stouter spines in the posterior cephalothoracic or trunk appendages, respectively. This differentiation indicates that crushing occurs posteriorly, while the gnathobases on anterior appendages continue mastication and push food towards and into the mouth. The results of recent phylogenetic analyses that considered both modern and fossil euarthropod clades show that xiphosurans and eurypterids are united as crown-group euchelicerates, with S. inexpectans placed within more basal artiopodan clades. These relationships suggest that gnathobases with thickened fibrous exocuticle, if not homoplasious, may be plesiomorphic for chelicerates and deeper relatives within Arachnomorpha. This study shows that the gnathobasic spine microstructure best adapted for durophagy has remained remarkably constant since the Cambrian.     

An integumental anatomy for the butterfly Glaucopsyche lygdamus (Lepidoptera:Lycaenidae):a morphological terminology and homology

An integumental anatomy for the lycaenid butterfly Glaucopsyche lygdamus is presented. Comparisons with other lepidopteran taxa are made to rectify the homology of parts and contrast anatomical divergences within the Lycaenidae. A general terminology based on Snodgrass is given, to replace many of the specialized and often synonymous terms restricted to the Lepidoptera. Many common anatomical svnonyms are also given. Several reinterpretations of the anatomy and homology of various integumental regions are discussed. A previously unreported cuticular anomaly on abdominal tergum 2 of male Polyommatinae (Downey's area) is described. The following new or newly combined terms are used:postgenal-occipital area, postgenal-occipital protuberance, dorsal temporal sulci, postantennal projections, pronotal projection, infraepisternal-basisternal plate, paracoxal-marginopleural sulci, dorsal epimeral sulci, ventral epimeral sulci, secondary coxal sulci, ventral subcostal-radial process, lateral secondary sclerite and Downey's area.