Controls on gut phosphatisation : the trilobites from the Weeks Formation Lagerstätte (Cambrian; Utah)

Despite being internal organs, digestive structures are frequently preserved in Cambrian Lagerstätten. However, the reasons for their fossilisation and their biological implications remain to be thoroughly explored. This is particularly true with arthropods--typically the most diverse fossilised organisms in Cambrian ecosystems--where digestive structures represent an as-yet underexploited alternative to appendage morphology for inferences on their biology. Here we describe the phosphatised digestive structures of three trilobite species from the Cambrian Weeks Formation Lagerstätte (Utah). Their exquisite, three-dimensional preservation reveals unique details on trilobite internal anatomy, such as the position of the mouth and the absence of a differentiated crop. In addition, the presence of paired pygidial organs of an unknown function is reported for the first time. This exceptional material enables exploration of the relationships between gut phosphatisation and the biology of organisms. Indeed, soft-tissue preservation is unusual in these fossils as it is restricted to the digestive structures, which indicates that the gut played a central role in its own phosphatisation. We hypothesize that the gut provided a microenvironment where special conditions could develop and harboured a source of phosphorus. The fact that gut phosphatization has almost exclusively been observed in arthropods could be explained by their uncommon ability to store ions (including phosphorous) in their digestive tissues. However, in some specimens from the Weeks Formation, the phosphatisation extends to the entire digestive system, suggesting that trilobites might have had some biological particularities not observed in modern arthropods. We speculate that one of them might have been an increased capacity for ion storage in the gut tissues, related to the moulting of their heavily-mineralised carapace

De novo assembly and characterization of a maternal and developmental transcriptome for the emerging model crustacean Parhyale hawaiensis

<p>Abstract</p> <p>Background</p> <p>Arthropods are the most diverse animal phylum, but their genomic resources are relatively few. While the genome of the branchiopod <it>Daphnia pulex </it>is now available, no other large-scale crustacean genomic resources are available for comparison. In particular, genomic resources are lacking for the most tractable laboratory model of crustacean development, the amphipod <it>Parhyale hawaiensis</it>. Insight into shared and divergent characters of crustacean genomes will facilitate interpretation of future developmental, biomedical, and ecological research using crustacean models.</p> <p>Results</p> <p>To generate a transcriptome enriched for maternally provided and zygotically transcribed developmental genes, we created cDNA from ovaries and embryos of <it>P. hawaiensis</it>. Using 454 pyrosequencing, we sequenced over 1.1 billion bases of this cDNA, and assembled them <it>de novo </it>to create, to our knowledge, the second largest crustacean genomic resource to date. We found an unusually high proportion of C2H2 zinc finger-containing transcripts, as has also been reported for the genome of the pea aphid <it>Acyrthosiphon pisum</it>. Consistent with previous reports, we detected trans-spliced transcripts, but found that they did not noticeably impact transcriptome assembly. Our assembly products yielded 19,067 unique BLAST hits against <b>nr </b>(E-value cutoff e-10). These included over 400 predicted transcripts with significant similarity to <it>D. pulex </it>sequences but not to sequences of any other animal. Annotation of several hundred genes revealed <it>P. hawaiensis </it>homologues of genes involved in development, gametogenesis, and a majority of the members of six major conserved metazoan signaling pathways.</p> <p>Conclusions</p> <p>The amphipod <it>P. hawaiensis </it>has higher transcript complexity than known insect transcriptomes, and trans-splicing does not appear to be a major contributor to this complexity. We discuss the importance of a reliable comparative genomic framework within which to consider findings from new crustacean models such as <it>D. pulex </it>and <it>P. hawaiensis</it>, as well as the need for development of further substantial crustacean genomic resources.</p

Global Biodiversity and Phylogenetic Evaluation of Remipedia (Crustacea)

Remipedia is one of the most recently discovered classes of crustaceans, first described in 1981 from anchialine caves in the Bahamas Archipelago. The class is divided into the order Enantiopoda, represented by two fossil species, and Nectiopoda, which contains all known extant remipedes. Since their discovery, the number of nectiopodan species has increased to 24, half of which were described during the last decade. Nectiopoda exhibit a disjunct global distribution pattern, with the highest abundance and diversity in the Caribbean region, and isolated species in the Canary Islands and in Western Australia. Our review of Remipedia provides an overview of their ecological characteristics, including a detailed list of all anchialine marine caves, from which species have been recorded. We discuss alternative hypotheses of the phylogenetic position of Remipedia within Arthropoda, and present first results of an ongoing molecular-phylogenetic analysis that do not support the monophyly of several nectiopodan taxa. We believe that a taxonomic revision of Remipedia is absolutely essential, and that a comprehensive revision should include a reappraisal of the fossil record

The brain of the Remipedia (Crustacea) and an alternative hypothesis on their phylogenetic relationships

Remipedia are rare and ancient mandibulate arthropods inhabiting almost inaccessible submerged cave systems. Their phylogenetic position is still enigmatic and the subject of extremely controversial debates. To contribute arguments to this discussion, we analyzed the brain of Godzilliognomus frondosus Yager, 1989 (Remipedia, Godzilliidae) and provide a detailed 3D reconstruction of its anatomy. This reconstruction yielded the surprising finding that in comparison with the brain of other crustaceans such as representatives of the Branchiopoda and Maxillopoda the brain of G. frondosus is highly organized and well differentiated. It is matched in complexity only by the brain of “higher” crustaceans (Malacostraca) and Hexapoda. A phylogenetic analysis limited to brain anatomy across the Mandibulata strongly contradicts the prevailing hypothesis that the Remipedia are a basal, ancestral crustacean group but instead argues in favor of a remipede-malacostracan-hexapod clade and most likely a sister-group relationship of Remipedia and Malacostraca

Simulation of the interaction of galactic cosmic-ray protons with meteoroids : on the production of radionuclides in thick gabbro and iron targets irradiated isotropically with 1.6 GeV protons

Thick spherical targets made of gabbro (R = 25 cm) and of steel (R = 10 cm) were irradiated isotropically with 1.6 GeV protons at the Saturne synchrotron at Laboratoire National Saturne (LNS)/CEN Saclay in order to simulate the interaction in space of galactic cosmic-ray (GCR) protons with stony and iron meteoroids. Proton fluences of 1.32 x 10(14) cm(-2) and 2.45 x 10(14) cm(-2) were received by the gabbro and iron sphere, respectively, which corresponds to cosmic-ray exposure ages of about 1.6 and 3.0 Ma. Both artificial meteoroids contained large numbers of high-purity target foils of up to 28 elements at different depths. In these individual target foils, elementary production rates of radionuclides and rare gas isotopes were measured by x- and gamma-spectrometry, by low-level counting, accelerator mass spectrometry (AMS), and by conventional rare gas mass spectrometry. Also samples of the gabbro itself were analyzed. Up to now, for each of the experiments, similar to 500 target-product combinations were investigated of which the results for radionuclides are presented here. The experimental production rates show a wide range of depth profiles reflecting the differences between low-, medium-, and high-energy products. The influence of the stony and iron matrices on the production of secondary particles and on particle transport, in general, and consequently on the production rates is clearly exhibited by the phenomenology of the production rates as well as by a detailed theoretical analysis. Theoretical production rates were calculated in an a priori way by folding depth-dependent spectra of primary and secondary protons and secondary neutrons calculated by Monte Carlo techniques with the excitation functions of the underlying nuclear reactions. Discrepancies of up to a factor of 2 between the experimental and a priori calculated depth profiles are attributed to the poor quality of the mostly theoretical neutron excitation functions. Improved neutron excitation functions were obtained by least-squares deconvolution techniques from experimental thick-target production rates of up to five thick-target experiments in which isotropic irradiations were performed. A posteriori calculations using the adjusted neutron cross sections describe the measured depth profiles of all these simulation experiments within 9%. The thus validated model calculations provide a basis for reliable physical model calculations of the production rates of cosmogenic nuclides in stony and iron meteorites as well as in lunar samples and terrestrial materials

Simulation of the interaction of galactic cosmic-ray protons with meteoroids : on the production of radionuclides in thick gabbro and iron targets irradiated isotropically with 1.6 GeV protons

Thick spherical targets made of gabbro (R = 25 cm) and of steel (R = 10 cm) were irradiated isotropically with 1.6 GeV protons at the Saturne synchrotron at Laboratoire National Saturne (LNS)/CEN Saclay in order to simulate the interaction in space of galactic cosmic-ray (GCR) protons with stony and iron meteoroids. Proton fluences of 1.32 x 10(14) cm(-2) and 2.45 x 10(14) cm(-2) were received by the gabbro and iron sphere, respectively, which corresponds to cosmic-ray exposure ages of about 1.6 and 3.0 Ma. Both artificial meteoroids contained large numbers of high-purity target foils of up to 28 elements at different depths. In these individual target foils, elementary production rates of radionuclides and rare gas isotopes were measured by x- and gamma-spectrometry, by low-level counting, accelerator mass spectrometry (AMS), and by conventional rare gas mass spectrometry. Also samples of the gabbro itself were analyzed. Up to now, for each of the experiments, similar to 500 target-product combinations were investigated of which the results for radionuclides are presented here. The experimental production rates show a wide range of depth profiles reflecting the differences between low-, medium-, and high-energy products. The influence of the stony and iron matrices on the production of secondary particles and on particle transport, in general, and consequently on the production rates is clearly exhibited by the phenomenology of the production rates as well as by a detailed theoretical analysis. Theoretical production rates were calculated in an a priori way by folding depth-dependent spectra of primary and secondary protons and secondary neutrons calculated by Monte Carlo techniques with the excitation functions of the underlying nuclear reactions. Discrepancies of up to a factor of 2 between the experimental and a priori calculated depth profiles are attributed to the poor quality of the mostly theoretical neutron excitation functions. Improved neutron excitation functions were obtained by least-squares deconvolution techniques from experimental thick-target production rates of up to five thick-target experiments in which isotropic irradiations were performed. A posteriori calculations using the adjusted neutron cross sections describe the measured depth profiles of all these simulation experiments within 9%. The thus validated model calculations provide a basis for reliable physical model calculations of the production rates of cosmogenic nuclides in stony and iron meteorites as well as in lunar samples and terrestrial materials