Biomass estimates of terrestrial arthropods based on body length

The relationship between body length and biomass (dry weight) was investigated for nineteen taxa of terres trail arthropods and for the combined sample that included all insect taxa. The specimens were collected from forests of Bicholim taluk of Goa. Four models were evaluated, a linear function, a logarithmic function, a power function and an exponential function. The linear function best describes dry weights in the order Isopoda of class Crustacea and dictyopteran, coleopteran larvae of class Insecta. The logarithmic function fits well for only one group namely Opiliones of class Arachnida. The power functions fits best for Scutigeromorpha and Scolopendromorpha of class Chilopoda, Araneae of class Arachnida, Collembola, Thysanura, Orthoptera, Hemiptera, Homoptera, coleopteran adults, Diptera, lepidopteran adults and Hymenoptera of class Insecta and the combined data on adult insects. An exponential function fits well for the dermapteran and lepidopteran larvae of class Insecta. The usefulness of these estimates of Arthropod biomass in community ecology is discussed.     

Convergent evolution and character correlation in burrowing reptiles: towards a resolution of squamate relationships

The affinities of three problematic groups of elongate, burrowing reptiles (amphisbaenians, dibamids and snakes) are reassessed through a phylogenetic analysis of all the major groups of squamates, including the important fossil taxa Sineoamphisbaena, mosasauroids and Pachyrhachis; 230 phylogenetically informative osteological characters were evaluated in 22 taxa. Snakes (including Pachyrhachis) are anguimorphs, being related firstly to large marine mosasauroids, and secondly to monitor lizards (varanids). Scincids and cordylids are not related to lacertiforms as previously thought, but to anguimorphs. Amphisbaenians and dibamids are closely related, and Sineoamphisbaena is the sister group to this clade. The amphisbaenian-dibamid-Sineoamphisbaena clade, in turn, is related to gekkotans and xantusiids. When the fossil taxa are ignored, snakes, amphisbaenians and dibamids form an apparently well-corroborated clade nested within anguimorphs. However, nearly all of the characters supporting this arrangement are correlated with head-first burrowing (miniaturization, cranial consolidation, body elongation, limb reduction), and invariably co-occur in other tetrapods with similar habits. These characters are potentially very misleading because of their sheer number and because they largely represent reductions or losses. It takes very drastic downweighting of these linked characters to alter tree topology: if fossils are excluded from the analysis, a (probably spurious) clade consisting of elongate, fossorial taxa almost always results. These results underscore the importance of including all relevant taxa in phylogenetic analyses. Inferring squamate phylogeny depends critically on the inclusion of certain (fossil) taxa with combinations of character states that demonstrate convergent evolution of the elongate, fossorial ecomorph in amphisbaenians and dibamids, and in snakes. In the all-taxon analysis, the position of snakes within anguimorphs is more strongly-corroborated than the association of amphisbaenians and dibamids with gekkotans. When the critical fossil taxa are deleted, snakes ‘attract’ the amphisbaenian-dibamid clade on the basis of a suite of correlated characters. While snakes remain anchored in anguimorphs, the amphisbaenian-dibamid clade moves away from gekkotans to join them. Regardless of the varying positions of the three elongate burrowing taxa, the interrelationships between the remaining limbed squamates (‘lizards’) are constant; thus, the heterodox affinities of scincids, cordylids, and xantusiids identified in this analysis appear to be robust. Finally, the position of Pachyrhachis as a basal snake rather than (as recently suggested) a derived snake is supported on both phylogenetic and evolutionary grounds.     

Multiplication of Chilo iridescent virus in noninsect arthropods

Attempts to infect noninsect arthropods with Chilo iridescent virus (CIV) originally isolated from Lepidoptera were made by using eight species belonging to four classes. Multiplication of CIV was demonstrated in two species of terrestrial Crustacea (the pill bug, Armadillidium vulgare, and the slater, Porcello scaber) and one species of Chilopoda, the house centipede, Thereuonema higendorfi. The lethality experiment of CIV for A. vulgare suggested that chronic infection is a characteristic of the CIV infection in both classes, Crustacea and Insecta. Neither iridescence nor recovery of virus infectivity was demonstrated in the following arthropod species: the sea slater, Ligia exotica (Crustacea: Isopoda), the grapsid crab, Sesarma haematocheir (Crustacea: Decapoda), the millipede, Oxidus gracillis (Diplopoda: Polydesmoidea), Rhysodesmus semicirculatus (Diplopoda: Polydesmoidea), and the giant crab spider, Heteropoda venatoria (Arachnida: Araneae).     

Character combinations, convergence and diversification in ectoparasitic arthropods

Different lineages of organisms diversify over time at different rates, in part as a consequence of the characteristics of the species in these lineages. Certain suites of traits possessed by species within a clade may determine rates of diversification, with some particular combinations of characters acting synergistically to either limit or promote diversification; the most successful combinations may also emerge repeatedly in different clades via convergent evolution. Here, the association between species characters and diversification is investigated amongst 21 independent lineages of arthropods ectoparasitic on vertebrate hosts. Using nine characters (each with two to four states) that capture general life history strategy, transmission mode and host-parasite interaction, each lineage was described by the set of character states it possesses. The results show, firstly, that most possible pair-wise combinations of character states have been adopted at least once, sometimes several times independently by different lineages; thus, ectoparasitic arthropods have explored most of the life history character space available to them. Secondly, lineages possessing commonly observed combinations of character states are not necessarily the ones that have experienced the highest rates of diversification (measured as a clade’s species-per-genus ratio). Thirdly, some specific traits are associated with higher rates of diversification. Using more than one host per generation, laying eggs away from the host and intermediate levels of fecundity are features that appear to have promoted diversification. These findings indicate that particular species characters may be evolutionary drivers of diversity, whose effects could also apply in other taxa.     

Phospholipids of sea worms,mollusks, and arthropods

The phospholipid composition of organs and tissues was investigated in representatives of five phyla of marine invertebrates: Annelida (Chaetopterus variopedatus, Serpula vermicularis), Echiuroidea (Urechis unicinctus), Sipunculoidea (Phascolosoma japonicum), Mollusca (Gastropoda: Tectonatica janthostoma, Neptunea polycostata; Bivalvia: Mactra sulcataria, Peronidia venuloza, Patinopecten yessoensis, Crenomytilus grayanus; Cephalopoda: Octopus conispadiceus, Todarodes pacificus), and Arthropoda (Paralythodes camtschatica, Erimacrus isenbekii, Hemigrapsus sanguineus, Pinixa rathbunii). The specificity of phospholipid distribution was shown to be related to the taxonomic position of marine invertebrates and functional properties of their organs and tissues. In Echiuroidea, Sipunculoidea, and Arthropoda, ceramide aminoethylphosphonate was found only in the digestive organs. This suggests an exogenous origin of this phospholipid.     

Primary structures of the 5S ribosomal RNAs of 11 arthropods and applicability of 5S RNA to the study of metazoan evolution

Summary 5S Ribosomal RNA sequences have proven to be useful tools in the study of evolutionary relationships among species. However, in reviewing previously published trees constructed from alignments of metazoan 5S RNAs, we noticed several discrepancies with classical evolutionary views. One such discrepancy concerned the phylum Arthropoda, where a crustacean,Artemia salina, seemed to be evolutionarily very remote from four insects. The cause of this phenomenon was studied by determining the 5S RNA sequences of additional arthropods, viz.Limulus polyphemus, Eurypelma californica, Lasiodora erythrocythara, Areneus diadematus, Daphnia magna, Ligia oceanica, Homarus gammarus, Cancer pagurus, Spirobolus sp.,Locusta migratoria, andTenebrio molitor. A tree was then constructed from a dissimilarity matrix by a clustering method known as weighted pair grouping. Application of a correction for unequal evolutionary rates improved the apparent evolutionary position of the arthropods and of some other metazoan species. However, neither the uncorrected nor the corrected tree permitted a completely acceptable reconstruction of metazoan evolution. We presume that this phenomenon is due to random deviations in the evolutionary rate of 5S RNA.Presented at the FEBS Symposium on Genome Organization and Evolution, held in Crete, Greece, September 1–5, 1986     

Origins and early evolution of herbivory in tetrapods

The first herbivorous tetrapods date from the Late Carboniferous, about 300 million years ago. By the Late Permian, continental ecosystems of `modern' aspect had been established, with a vast standing crop of herbivores supporting relatively few carnivores. Processing of high-fibre plant material requires (1) structural modifications of the dentition, jaw apparatus and digestive tract and (2) the acquisition of microbial endosymbionts that produce the enzymes needed for fermentative digestion of cellulose, the principal compound of cell walls in plants. Recent phylogenetic analyses of tetrapods indicate that endosymbiotic cellulysis was acquired independently in a number of lineages during the late Palaeozoic.     

Draft genomes and genomic divergence of two Lepidurus tadpole shrimp species (Crustacea,Branchiopoda, Notostraca)

Crustaceans of the order Notostraca (Branchiopoda) are distributed worldwide and are known for the remarkable morphological stasis between their extant and Permian fossil species. Moreover, these crustaceans show relevant ecological traits and a wide range of reproductive strategies. However, genomic studies on notostracans are fairly limited. Here, we present the genome sequences of two notostracan taxa, Lepidurus arcticus and Lepidurus apus lubbocki. Taking advantage of the small genome sizes (~0.11 pg) of these taxa, genomes were sequenced for one individual per species with one run on the Illumina HiSeq X platform. We finally assembled 73.2 Mbp (L. arcticus) and 90.3 Mbp (L. apus lubbocki) long genomes. Assemblies cover up to 84% of the estimated genome size, with a gene completeness >97% for both genomes. In total, 13%–16% of the assembled genomes consist of repeats, and based on read mapping, L. apus lubbocki shows a significantly lower transposable element content than L. arcticus. The analysis of 2,376 orthologous genes indicates an ~7% divergence between the two Lepidurus taxa, with a nucleotide substitution rate significantly lower than that of Daphnia taxa. K_a/K_s analysis suggests purifying selection in both branchiopod lineages, raising the question of whether the low substitution rate of Lepidurus is correlated with morphological conservation or is linked to specific biological traits. Our analysis demonstrates that, in these organisms, it is possible to obtain high‐quality draft genomes from single individuals with a relatively low sequencing effort. This result makes Lepidurus and Notostraca interesting models for genomic studies at taxonomic, ecological and evolutionary levels.     

Trace fossils of Cambrian aglaspidid arthropods

A new trace fossil, Raaschichnus gundersoni , from the Upper Cambrian St. Lawrence Formation of Wisconsin, was produced by an aglaspidid arthropod. The rusophyciform trace, which occurs singly and in series, is distinctive in showing marks left by the tail-spine. Other trace fossils previously considered to have been made by aglaspidids were probably excavated by animals lacking a tail-spine and with appendage morphologies very different from the aglaspidids of Wisconsin.     

Origins and biomechanical evolution of teeth in echinoids and their relatives

Abstract:  Echinoid teeth are without doubt the most complex and highly specialized skeletal component to have evolved in echinoderms. They are biomechanically constructed to be resilient and tough while maintaining a self-sharpening point. Based on SEM analysis of isolated tooth elements collected primarily from the Ordovician and Silurian of Gotland, we provide a detailed structural analysis of the earliest echinoderm teeth. Eight distinct constructional designs are recognized encompassing various degrees of sophistication, from a simple vertical battery of tooth spines to advanced teeth with multiple tooth plate series and a reinforced core of fibres. These provide key data from which we reconstruct the early stages of tooth evolution. The simplest teeth are composed of stacked rod-like elements with solid calcite tips. More advanced teeth underwent continuous replacement of tooth elements, as a simple self-sharpening mechanism. Within echinoids tooth design was refined by evolving thinner, flatter primary plates with buttressing, allowing maintenance of a sharper and stronger biting edge. Despite the obvious homology between the lanterns of ophiocistioids and echinoids, their teeth are very different in microstructural organization, and they have evolved different self-sharpening mechanisms. Whereas echinoid teeth evolved from a biseries of mouth spines, ophiocistioid goniodonts evolved from a single series of mouth spines. Rogeriserra represents the most primitive known battery of tooth elements but its taxonomic affinities remain unknown.     

Comparative experimental taphonomy of eight marine arthropods indicates distinct differences in preservation potential

Global biodiversity patterns in deep time can only be understood fully when the relative preservation potential of each clade is known. The relative preservation potential of marine arthropod clades, a diverse and ecologically important component of modern and past ecosystems, is poorly known. We tackled this issue by carrying out a 205‐day long comprehensive, comparative, taphonomic experiment in a laboratory by scoring up to ten taphonomic characters for multiple specimens of seven crustacean and one chelicerate species (two true crabs, one shrimp, one lobster, one hermit crab, one stomatopod, one barnacle and one horseshoe crab). Although the results are preliminary because we used a single experimental setup and algal growth partially hampered observations, some parts of hermit crabs, stomatopods, swimming crabs and barnacles decayed slowly relative to other parts, implying differential preservation potentials within species, largely consistent with the fossil record of these groups. An inferred parasitic isopod, manifested by a bopyriform swelling within a hermit crab carapace, decayed relatively fast. We found limited variation in the decay rate between conspecifics, and we did not observe size‐related trends in decay rate. Conversely, substantial differences in the decay rate between species were seen after c. 50 days, with shrimps and stomatopods decaying fastest, suggesting a relatively low preservation potential, whereas the lobster, calico crabs, horseshoe crabs and barnacles showed relatively slow decay rates, suggesting a higher preservation potential. These results are supported by two modern and fossil record‐based preservation potential metrics that are significantly correlated to decay rate ranks. Furthermore, we speculate that stemward slippage may not be ubiquitous in marine arthropods. Our results imply that diversity studies of true crabs, lobsters, horseshoe crabs and barnacles are more likely to yield patterns that are closer to their true biodiversity patterns than those for stomatopods, shrimps and hermit crabs.     

节肢动物的分类和演化

节肢动物门是动物界中最大的1个门。按新的分类系统,本门分三叶虫亚门(已灭绝)、螯肢亚门、甲壳亚门、六足亚门和多足亚门等5亚门。六足亚门相当于以前分类系统中的昆虫纲(广义的), 是最重要的一类节肢动物;此亚门分原尾纲、弹尾纲、双尾纲和昆虫纲(狭义的)等4纲;昆虫纲分3亚纲30目,包括了前昆虫纲“有翅亚纲”中的各目。为便于读者了解新、旧系统的异同,文中列举前人的代表性系统加以对照。同时,对学术界关于节肢动物的起源和演化的一些新观点予以必要的说明,对现时流行的“泛节肢动物”、“泛甲壳动物”等概念作了简要的介绍。     

Systematics of the spider genus Metabus O. P.-Cambridge, 1899 (Araneoidea: Tetragnathidae) with additions to the tetragnathid fauna of Chile and comments on the phylogeny of Tetragnathidae

The spider genus Metabus (Tetragnathidae) previously included nine species: the type M. gravidus O. P.-Cambridge, 1899 – junior synonym of Leucauge ocellata (Keyserling) – from Central America and eight species from Chile. In this paper, the classification of the Metabus species-complex is revised, and two new genera, with three new species and five new combinations, are described. Allende gen. nov. is created for four Chilean species not congeneric with the type of Metabus : the type A. puyehuensis sp. nov. , A. patagiatus (Simon) comb. nov. , A. nigrohumeralis (F. O. P.-Cambridge) comb. nov. and A. longipes (Nicolet) comb. nov. Further additions to the Chilean fauna are under the new genus Mollemeta gen. nov. – created for M. edwardsi (Simon) comb. nov. – and three new species of Chrysometa : C. acinosa sp. nov. , C. levii sp. nov. and C. maitae sp. nov. Metabus now includes four species: M. ocellatus (Keyserling) comb. nov. , M. debilis (O. P.-Cambridge) comb. nov. , M. ebanoverde sp. nov. and M. conacyt sp. nov. All of these species were included in a phylogenetic analysis of 38 tetragnathid and 12 orbicularian outgroup terminals scored for 105 morphological and behavioural characters. The results suggest that Metabus as previously circumscribed is polyphyletic. The phylogenetic relationships within tetragnathids are briefly discussed. © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society , 2007, 151 , 285–335.     

Digestive system and feeding mode in Cambrian naraoiid arthropods

The function of the digestive system of naraoiid arthropods is interpreted in the light of new observations on Early Cambrian specimens from China and detailed comparisons with Recent crustaceans and other arthropods. In naraoiids, paired tubular diverticulae ending as blind caeca are present along the entire midgut, and are interpreted as sites for the secretion of digestive enzymes. Naraoia bears one pair of long, ramifying, distensible diverticulae, possibly used for both food storage and digestion as suggested by Recent analogues (e.g. branchiuran and isopod crustaceans and limulids). Naraoiids were probably epibenthic scavengers/predators rather than mud-eaters. They were either opportunistic intermittent feeders ( Naraoia ) or more regular feeders ( Misszhouia ). The mud-fills of the alimentary canals are likely to be artefacts due to taphonomic and weathering processes or, less likely, to sediment ingestion by animals trapped alive in turbiditic flows. The case study of naraoiid arthropods adds to other fossil evidence supporting the idea that predation played a key role in the Early Cambrian food-webs and that organs adapted for this purpose had already reached a high level of diversity and anatomical sophistication.     

Phylogeny and systematic position of Opiliones: a combined analysis of chelicerate relationships using morphological and molecular data

The ordinal level phylogeny of the Arachnida and the suprafamilial level phylogeny of the Opiliones were studied on the basis of a combined analysis of 253 morphological characters, the complete sequence of the 18S rRNA gene, and the D3 region of the 28S rRNA gene. Molecular data were collected for 63 terminal taxa. Morphological data were collected for 35 exemplar taxa of Opiliones, but groundplans were applied to some of the remaining chelicerate groups. Six extinct terminals, including Paleozoic scorpions, are scored for morphological characters. The data were analyzed using strict parsimony for the morphological data matrix and via direct optimization for the molecular and combined data matrices. A sensitivity analysis of 15 parameter sets was undertaken, and character congruence was used as the optimality criterion to choose among competing hypotheses. The results obtained are unstable for the high-level chelicerate relationships (except for Tetrapulmonata, Pedipalpi, and Camarostomata), and the sister group of the Opiliones is not clearly established, although the monophyly of Dromopoda is supported under many parameter sets. However, the internal phylogeny of the Opiliones is robust to parameter choice and allows the discarding of previous hypotheses of opilionid phylogeny such as the "Cyphopalpatores" or "Palpatores." The topology obtained is congruent with the previous hypothesis of "Palpatores" paraphyly as follows: (Cyphophthalmi (Eupnoi (Dyspnoi + Laniatores))). Resolution within the Eupnoi, Dyspnoi, and Laniatores (the latter two united as Dyspnolaniatores nov.) is also stable to the superfamily level, permitting a new classification system for the Opiliones.     

The evolution of the Ecdysozoa

Ecdysozoa is a clade composed of eight phyla: the arthropods, tardigrades and onychophorans that share segmentation and appendages and the nematodes, nematomorphs, priapulids, kinorhynchs and loriciferans, which are worms with an anterior proboscis or introvert. Ecdysozoa contains the vast majority of animal species and there is a great diversity of body plans among both living and fossil members. The monophyly of the clade has been called into question by some workers based on analyses of whole genome datasets. We review the evidence that now conclusively supports the unique origin of these phyla. Relationships within Ecdysozoa are also controversial and we discuss the molecular and morphological evidence for a number of monophyletic groups within this superphylum.     

The evolution of arthropod limbs

Limb morphology across the arthropods is reviewed using external morphological and internal anatomical data from both recent and fossil arthropods. Evolutionary trends in limb structure are identified primarily by reference to the more rigorous of the many existing phylogenetic schemes, but no major new phylogenetic inferences are presented. Tagmosis patterns are not considered, although the origins and patterns of heteronomy within the postantennulary limb series are analysed. The phenomenon of annulation is examined and two basic types of annuli are recognised: terminal and intercalary. The annulation of the apical segment of a limb results in the formation of terminal flagella, and is typical of primarily sensory appendages such as insect and malacostracan antennules and maxillary palps of some hexapods. Intercalary annulation, arising by subdivision of existing subterminal segments, is common, particularly in the tarsal region of arthropodan walking limbs. Differentiating between segments and annuli is discussed and is recognised as a limiting factor in the interpretation of fossils, which usually lack information on intrinsic musculature, and in the construction of groundplans. Rare examples of secondary segmentation, where the criteria for distinguishing between segments and annuli fail, are also highlighted. The basic crown-group arthropodan limb is identified as tripartite, comprising protopodite, telopodite and exopodite, and the basic segmentation patterns of each of these parts are hypothesised. Possible criteria are discussed that can be used for establishing the boundary between protopodite and telopodite in limbs that are uniramous through loss of the exopodite. The subdivision of the protopodite, which is typical of the postantennulary limbs of mandibulates, is examined. The difficulties resulting from the partial or complete failure of expression of articulations within the mandibulate protopodite and subsequent incorporation of partial protopodal segments into the body wall, are also discussed. The development and homology between the various exites, including gills, on the postantennulary limbs of arthropods are considered in some detail, and the question of the possible homology between crustacean gills and insect wings is critically addressed. The hypothesis that there are only two basic limb types in arthropods, antennules and postantennulary limbs, is proposed and its apparent contradiction by the transformation of antennules into walking limbs by homeotic mutation is discussed with respect to the appropriate level of serial homology between these limbs.     

Taphonomic experiments imply a possible link between the evolution of multicellularity and the fossilization potential of soft‐bodied organisms

The reliability of evolutionary reconstructions based on the fossil record critically depends on our knowledge of the factors affecting the fossilization of soft‐bodied organisms. Despite considerable research effort, these factors are still poorly understood. In order to elucidate the main prerequisites for the preservation of soft‐bodied organisms, we conducted long‐term (1–5 years) taphonomic experiments with the model crustacean Artemia salina buried in five different sediments. The subsequent analysis of the carcasses and sediments revealed that, in our experimental settings, better preservation was associated with the fast deposition of aluminum and silicon on organic tissues. Other elements such as calcium, magnesium, and iron, which can also accumulate quickly on the carcasses, appear to be much less efficient in preventing decay. Next, we asked if the carcasses of uni‐ and multicellular organisms differ in their ability to accumulate aluminum ions on their surface. The experiments with the flagellate Euglena gracilis and the sponge Spongilla lacustris showed that aluminum ions are more readily deposited onto a multicellular body. This was further confirmed by the experiments with uni‐ and multicellular stages of the social ameba Dictyostelium discoideum. The results lead us to speculate that the evolution of cell adhesion molecules, which provide efficient cell–cell and cell–substrate binding, probably can explain the rich fossil record of soft‐bodied animals, the comparatively poor fossil record of nonskeletal unicellular eukaryotes, and the explosive emergence of the Cambrian diversity of soft‐bodied fossils.