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Fossilized embryos afford direct insight into the pattern of development in extinct organisms, providing unique tests of hypotheses of developmental evolution based in comparative embryology. However, these fossils can only be effective in this role if their embryology and phylogenetic affinities are well constrained. We elucidate and interpret the development of Olivooides from embryonic and adult stages and use these data to discriminate among competing interpretations of their anatomy and affinity. The embryology of Olivooides is principally characterized by the development of an ornamented periderm that initially forms externally and is subsequently formed internally, released at the aperture, facilitating the direct development of the embryo into an adult theca. Internal anatomy is known only from embryonic stages, revealing two internal tissue layers, the innermost of which is developed into three transversally arranged walls that partly divide the lumen into an abapertural region, interpreted as the gut of a polyp, and an adapertural region that includes structures that resemble the peridermal teeth of coronate scyphozoans. The anatomy and pattern of development exhibited by Olivooides appears common to the other known genus of olivooid, Quadrapyrgites, which differs in its tetraradial, as opposed to pentaradial symmetry. We reject previous interpretations of the olivooids as cycloneuralians, principally on the grounds that they lack a through gut and introvert, in embryo and adult. Instead we consider the affinities of the olivooids among medusozoan cnidarians; our phylogenetic analysis supports their classification as totalgroup Coronata, within crown-Scyphozoa. Olivooides and Quadrapyrgites evidence a broader range of life history strategies and bodyplan symmetry than is otherwise commonly represented in extant Scyphozoa specifically, and Cnidaria more generally.Key words: development, embryo, Cnidaria, Scyphozoa, Kuanchuanpu, Cambrian. et al. 2015), the tempo of early animal evolution is astonishing given the scale of innovation achieved (Erwin et al. 2011): the establishment of all phylum-level body plans that are sufficiently distinct that they are effectively defined by the limits of comparative anatomy (Bengtson 1986). Insights into the processes that brought about this remarkable episode in evolutionary history are afforded through comparative embryology of living animals, facilitating inference of the embryology of ancient ancestors and, indeed, into the evolution of development that brought about the origin of animal bodyplans. Inevitably, this approach is confused by the subsequent developmental evolution that serves to conflate homologies and convergences. Hence, the discovery of a fossil record of embryology from early in animal evolutionary history affords a more direct insight into the embryology of ancient ancestors, free from the confounding effects of half a billion years of subsequent evolutionary history. T H O U G H there remains considerable debate over the timing of ori...

General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/pure/about/ebr-terms A R T I C L E I N F OKeywords: Fossil embryo Doushantuo Animal Evolution Ediacaran A B S T R A C TThe embryo-like microfossils from the Ediacaran Weng'an Biota (ca. 609 million years old) are among the oldest plausible claims of animals in the fossil record. Fossilization frequently extends beyond the cellular, to preserve subcellular structures including contentious Large Intracellular Structures (LISs) that have been alternately interpreted as eukaryote nuclei or organelles, degraded remains, or abiological structures. Here we present new data on the structure, morphology, and development of the LISs in these embryo-like fossils, based on Synchrotron Radiation X-ray Tomographic Microscopy (SRXTM) and quantitative computed tomographic analysis. All the lines of evidence, including consistency in the number, shape, position, and relative size (LIS-tocytoplasm ratio) of the LISs, as well as their occurrence within preserved cytoplasm, support their interpretation as cell nuclei. Our results allow us to reject the view that nuclei cannot be preserved in early eukaryote fossils, offering new potential for interpreting the fossil record of early eukaryote evolution.

Early Cambrian Pseudooides prima has been described from embryonic and post-embryonic stages of development, exhibiting long germ-band development. There has been some debate about the pattern of segmentation, but this interpretation, as among the earliest records of ecdysozoans, has been generally accepted. Here, we show that the ‘germ band’ of P. prima embryos separates along its mid axis during development, with the transverse furrows between the ‘somites’ unfolding into the polar aperture of the ten-sided theca of Hexaconularia sichuanensis, conventionally interpreted as a scyphozoan cnidarian; co-occurring post-embryonic remains of ecdysozoans are unrelated. We recognize H. sichuanensis as a junior synonym of P. prima as a consequence of identifying these two form-taxa as distinct developmental stages of the same organism. Direct development in P. prima parallels the co-occuring olivooids Olivooides, and Quadrapyrgites and Bayesian phylogenetic analysis of a novel phenotype dataset indicates that, despite differences in their tetra-, penta- and pseudo-hexa-radial symmetry, these hexangulaconulariids comprise a clade of scyphozoan medusozoans, with Arthrochites and conulariids, that all exhibit direct development from embryo to thecate polyp. The affinity of hexangulaconulariids and olivooids to extant scyphozoan medusozoans indicates that the prevalence of tetraradial symmetry and indirect development are a vestige of a broader spectrum of body-plan symmetries and developmental modes that was manifest in their early Phanerozoic counterparts.

The Ediacaran Weng'an Biota (Doushantuo Formation, 609 million years old) is a rich microfossil assemblage that preserves biological structure to a subcellular level of fidelity and encompasses a range of developmental stages [1]. However, the animal embryo interpretation of the main components of the biota has been the subject of controversy [2, 3]. Here we describe the development of Caveasphaera, which varies in morphology from lensoid, to a hollow spheroidal cage [4], to a solid spheroid [5], but has largely evaded description and interpretation. Caveasphaera is demonstrably cellular and develops within an envelope by cell division and migration, first defining the spheroidal perimeter via anastomosing cell masses that thicken and ingress as strands of cells that detach and subsequently aggregate in the polar region. Concomitantly, the overall diameter increases as does the volume of the cell mass but, after an initial phase of reductive palinotomy, the volume of individual cells remains the same through development. The process of cell ingression, detachment and polar aggregation is analogous to gastrulation; together with evidence of functional cell adhesion and development within an envelope, this is suggestive of a holozoan affinity. Maternal investment in the embryonic development of Caveasphaera and co-occuring Tianzhushania and Spiralicellula, as well as delayed onset of later development, may reflect an adaptation to the heterogeneous nature of the early Ediacaran nearshore marine environments in which early animals evolved. RESULTS The Weng'an biota provides a unique insight into multicellular life in the early Ediacaran period during which molecular clocks estimate the fundamental animal lineages to have diverged [6]. Indeed, there are numerous claims of animal remains from the biota, including miniature adult eumetazoans [7] and bilaterians [8], and embryonic animals [2, 9-12], but all remain contentious [3, 13-18]. However, there is a broader diversity of fossil remains from this deposit that have been the subject of little attention, some of which may have a greater claim on animal affinity. These fossils include Caveasphaera costata (Figure 1) which has been described as a spherical hollow cage (Figure 1A-C) [4] to a more solid sphere (Figure 1D) [5] of unknown nature and affinity, though superficial comparison has been drawn to embryos of an octocoral [4]. Analysis of the structure and development of Caveasphaera is challenging because of its small size and complex morphology. We employed Synchrotron Radiation X-ray Tomographic Microscopy (srXTM) [19] and High resolution Xray microtomography [20] to analyse 233 specimens of Caveasphaera that encompass its morphological and size range, based on a rich fossil assemblage from '54' and Datang quarries in the

Molecular clock analyses estimate that crown-group animals began diversifying hundreds of millions of years before the start of the Cambrian period. However, the fossil record has not yielded unequivocal evidence for animals during this interval. Some of the most promising candidates for Precambrian animals occur in the Weng'an biota of South China, including a suite of tubular fossils assigned to Sinocyclocyclicus, Ramitubus, Crassitubus and Quadratitubus, that have been interpreted as soft-bodied eumetazoans comparable to tabulate corals. Here, we present new insights into the anatomy, original composition and phylogenetic affinities of these taxa based on data from synchrotron radiation X-ray tomographic microscopy, ptychographic nanotomography, scanning electron microscopy and electron probe microanalysis. The patterns of deformation observed suggest that the cross walls of Sinocyclocyclicus and Quadratitubus were more rigid than those of Ramitubus and Crassitubus. Ramitubus and Crassitubus specimens preserve enigmatic cellular clusters at terminal positions in the tubes. Specimens of Sinocyclocyclicus and Ramitubus have biological features that might be cellular tissue or subcellular structures filling the spaces between the cross walls. These observations are incompatible with a cnidarian interpretation, in which the spaces between cross walls are abandoned parts of the former living positions of the polyp. The affinity of the Weng'an tubular fossils may lie within the algae.

Allozyme variation of the littleneck clam Ruditapes philippinarum was evaluated in four samples from Nameishi and Matsuo in the Ariake Sea, Ryugatake and Ushibuka in the Shiranui Sea off Kyushu Island, Japan, and in one sample from Jinzhou, China, in the Bohai Sea. A Ruditapes bruguieri sample imported from the Korean Bay off Nampo, North Korea was also studied. Among the R. philippinarum samples, heterozygosity varied from 0.265 to 0.301 and FIS estimates indicated significant homozygosity excess in 15 of 40 loci analyzed. Deviations from Hardy-Weinberg equilibrium were significant in all samples (P < 0.05). Pairwise FST estimates indicate that genetic differences between the Chinese and Japanese samples were very low, but significantly different from zero. Mixture proportions with 95% confidence intervals of Chinese R. philippinarum in Nameishi and Matsuo were estimated at 0.4098 [0.2512, 0.5705] and 0.4899 [0.3262, 0.6540], respectively. However, genetic invasion of stocked Chinese R. philippinarum into wild populations in the Ariake Sea remains uncertain due to the low precision of the estimates caused by the high similarity of allele frequencies between Jinzhou and the Ariake Sea.

ABSTRACT. Ge nera l features of the reprod uction a nd pop ulation dyna mics of Chiollepubera(Bon Sai nt-Vicent) (Biva lvia, Ve neridae) in So uth Brazil . Material collected with a 2-meter wide beam trawl during eight survey s condllcted ti'om December 1995 to Febrllary 1997 was llsed for a tirst preliminary desc ription 01' the reproduction and poplIlation dynamics of the edible venerid biva lve Chione pllbera (Bory Saint-Vicent, 1827). Greatest catches were found between 30 to 35 meters depth, on fine sandy bottoms with a mlld content lower than 10%. Dly we ight meat condition index showed highest va lues during alltumn and lowest vallles from winter to sumllle r lllonths. Histological analysis 01' gonadal tisslle showed a continuous rcproduction , with peaks of maturation on autumn and spring. Spawning was related with th e increase ofwater telllperature, that occurs twice a year in the region as a consequence ora particular hydrological characteristic of the inncr continental shelf. Size fi'equency distribution showed a uniqllc principallllode with slow ir any di splaccmcnt throllgh timc, indicating a long livcd spec ies. KEY WORDS. Ciliolle p"bera, reproducti on, vencrid , so uth Brazil A famí lia Veneridae reúne um grupo de bivalves muito apreciados pelo de licado sabo r da s ua carne. Mu itas espécies s ão extensivamente pescadas em di Cerentes costas do mundo, tendo s ido dese nvolvido também com s ucesso o cu ltivo das mes mas. Um exemplo bem conhecido é o de Mercenaria mercenaria (Li nnaeu s, 1758) no Atlântico norte (CARRIKER 1959). Esta espécie representa um importante recurso pesq ueiro, existindo numerosos estudos so bre a sua biologia e ecologia popu lacional , constituindo hoje um dos venerideos melhor estudados (LOOSANOFF 1937 ;