Biotic interaction between spionid polychaetes and bouchardiid brachiopods: Paleoecological, taphonomic and evolutionary implications

Shells of Bouchardia rosea (Brachiopoda, Rhynchonelliformea) are abundant in Late Holocene death assemblages of the Ubatuba Bight, Brazil, SW Atlantic. This genus is also known from multiple localities in the Cenozoic fossil record of South America. A total of 1211 valves of B. rosea, 2086 shells of sympatric bivalve mollusks (14 nearshore localities ranging in depth from 0 to 30 m), 80 shells of Bouchardia zitteli, San Julián Formation, Paleogene, Argentina, and 135 shells of Bouchardia transplatina, Camacho Formation, Neogene, Uruguay were examined for bioerosion traces. All examined bouchardiid shells represent shallow-water, subtropical marine settings. Out of 1211 brachiopod shells of B. rosea, 1201 represent dead individuals. A total of 149 dead specimens displayed polychaete traces (Caulostrepsis). Live polychaetes were found inside Caulostrepsis borings in 10 life-collected brachiopods, indicating a syn-vivo interaction (Caulostrepsis traces in dead shells of B. rosea were always empty). The long and coiled peristomial palps, large chaetae on both sides of the 5th segment, and flanged pygidium found in the polychaetes are characteristic of the polychaete genus Polydora (Spionidae). The fact that 100% of the Caulostrepsis found in living brachiopods were still inhabited by the trace-making spionids, whereas none was found in dead hosts, implies active biotic interaction between the two living organisms rather than colonization of dead brachiopod shells. The absence of blisters, the lack of valve/site stereotypy, and the fact that tubes open only externally are all suggestive of a commensal relationship. These data document a new host group (bouchardiid rhynchonelliform brachiopods) with which spionids can interact (interestingly, spionid-infested sympatric bivalves have not been found in the study area despite extensive sampling). The syn-vivo interaction indicates that substantial bioerosion may occur when the host is alive. Thus, the presence of such bioerosion traces on fossil shells need not imply a prolonged post-mortem exposure of shells on the sea floor. Also, none of the Paleogene and Neogene Bouchardia species included any ichnological evidence for spionid infestation. This indicates that the Spionidae/ Bouchardia association may be geologically young, although the lack of older records may also reflect limited sampling and/or taphonomic biases.

A new permian bivalve (Megadesmidae, Plesiocyprinellinae) from the Serrinha member, Rio do Rasto Formation, Paraná Basin, Brazil

During a recent inspection in the Paleontological Collection of the Institute of Geosciences, University of São Paulo, we have identifi ed some specimens of undescribed mollusk bivalves. These called our attention for the following reasons: a) all specimens are internal molds of conjugated and closed articulated valves, some of them presenting fragments of silicifi ed shells; b) all internal molds have similar general shape and internal characters, representing specimens of the same taxon; c) the internal molds and silicifi ed valves are well preserved, including fragile structures, which are hardly preserved, such as the internal mold of the external ligament and muscle scars; d) and equally important, according to the labels of all specimens, they were collected from rocks of the Passa Dois Group (Permian), Serrinha Member of the Rio do Rasto Formation. Although who collected the shells and the precise geographic location of the specimens are still unknown, the detailed study of these fossils brings us to the conclusion that they are morphologically distinct from any heretofore published genus of the endemic fauna of bivalves from Passa Dois Group. Based in its general shape, hinge structure and muscles scars, the new form can be classifi ed under the Family Megadesmidae Vokes, 1967, the most diverse group of Permian bivalves of the Paraná Basin. The specimens are referred as Beurlenella elongatella new gen. and sp. The shell shape and taphonomy indicate that this bivalve was a shallow, rapid, active burrower, suspension feeder, probably preserved in situ, in event deposits.

Life mode of in situ Conularia in a Middle Devonian epibole

Exceptionally abundant specimens of Conularia aff. desiderata Hall occur in multiple marine obrution deposits, in a single sixth-order parasequence composed of argillaceous and silty very fine sandstone, in the Otsego Member of the Mount Marion Formation (Middle Devonian, Givetian) in eastern New York State, USA. Associated fossils consist mostly of rhynchonelliform brachiopods but also include bivalve molluscs, orthoconic nautiloids, linguliform brachiopods and gastropods. Many of the brachiopods, bivalve molluscs and conulariids have been buried in situ. Conulariids buried in situ are oriented with their aperture facing obliquely upward and with their long axis inclined at up to 87degree to bedding. Most specimens are solitary, but some occur in V-like pairs or in radial clusters consisting of three specimens, with the component specimens being about equally long or (less frequently) substantially different in length. The compacted apical end of Conularia buried in situ generally rests upon argillaceous sandstone. With one possible exception, none of the examined specimens terminates in a schott (apical wall), and internal schotts appear to be absent. The apical ends of specimens in V-like pairs and radial clusters show no direct evidence of interconnection of their periderms. The apical, middle or apertural region of some inclined specimens abuts or is in close lateral proximity to a recumbent conulariid or to one or more spiriferid brachiopods, some of which have been buried in their original life orientation. The azimuthal bearings of Conularia and nautiloid long axes and the directions in which conulariids open are nonrandom, with conulariids being preferentially aligned between 350 and 50degree and with their apertural end facing north-east, and nautiloids being preferentially aligned between 30 and 70degree. Otsego Member Conularia were erect or semi-erect, epifaunal or partially infaunal animals, the apical end of which rested upon very fine bottom sediment. The origin of V-like pairs and radial clusters remains enigmatic, but it is probable that production of schotts was not a regular feature of this animal's life history. Finally, conulariids and associated fauna were occasionally smothered by distal storm deposits, under the influence of relatively weak bottom currents. © The Palaeontological Association.

Bivalves permianos da fase de continentalização das bacias do Gondwana Ocidental: sistemática, paleogeografia e bioestratigrafia

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Early Permian post-glacial bivalve faunas of the Itarare Group, Parana Basin, Brazil: Paleoecology and biocorrelations with South American intraplate basins

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Caracterização estrutural e funcional da comunidade do costão rochoso da praia da Feiticeira, Ilhabela: contribuição para avaliação de impactos gerados por vazamento de óleo

Costões rochosos são ecossistemas que propiciam o desenvolvimento de comunidades com grande riqueza de espécies e são ambientes de muita importância para a manutenção dos ecossistemas costeiros. Tais ambientes estão extremamente sujeitos a impactos antrópicos, principalmente no que se refere às contaminações por petróleo. O município da Ilhabela concentra o maior número de costões do Estado de São Paulo, e apresenta um notável histórico desses derrames. A fim de contribuir com o monitoramento dos costões da área do Canal de São Sebastião executado pela CETESB, o presente trabalho tem como objetivo central o estudo da estrutura da comunidade do costão rochoso da Praia da Feiticeira, um dos pontos monitorados pela CETESB entre 1993 e 1996. Além da caracterização das variáveis abióticas, a metodologia, com relação as variáveis biológicas, foi dividida em três partes: estudo quantitativo das espécies dominantes da macrofauna séssil encontradas no campo, baseado na porcentagem de cobertura de Chthamalus bisinuatus (Cirripedia), Brachidontes sp. (Bivalvia) e Tetraclita stalactifera (Cirripedia), gerando gráficos sazonais e demográficos. Para aprimorar as comparações entre os dois trabalhos, foi feito o Teste de hipótese para igualdade de proporções, comparando ano a ano as coletas de inverno, que mostrou que as três espécies dominantes obtiveram mudanças de um trabalho para o outro, rejeitando assim a Ho em todas as situações; estudo qualitativo das espécies de macrofauna e macroalgas encontradas dentro da área amostrada. Este levantamento resultou em uma lista de espécies que foi adicionada ao inventário do programa de monitoramento. O índice de similaridade entre os dois trabalhos foi determinado segundo o coeficiente de Sorrensen, que mostrou uma similaridade média entre as comunidades. Estas espécie ...(Resumo completo, clicar acesso eletrônico abaixo)

Permian non-marine bivalves of the Falkland Islands and their palaeoenvironmental significance

We describe the occurrence of non-marine bivalves in exposures of the Middle Permian (Capitanian) Brenton Loch Formation on the southern shore of Choiseul Sound, East Falklands. The bivalves are associated with ichnofossils and were collected from a bed in the upper part of the formation, within a 25 cm thick interval of dark siltstones and mudstones with planar lamination, overlain by massive sandstones. The shells are articulated, with the valves either splayed open or closed. At the top of the succession, mudstone beds nearly 1.5 m above the bivalve-bearing layers yielded well-preserved Glossopteris sp. cf. G. communis leaf fossils. The closed articulated condition of some shells indicates preservation under high sedimentation rates with low residence time of bioclasts at the sediment/water interface. However, the presence of specimens with splayed shells is usually correlated to the slow decay of the shell ligament in oxygen-deficient bottom waters. The presence of complete carbonized leaves of Glossopteris associated with the bivalve-bearing levels also suggests a possibly dysoxic-anoxic bottom environment. Overall, our data suggest that the bivalves were preserved by abrupt burial, possibly by distal sediment flows into a Brenton Loch lake, and may represent autochthonous to parautochthonous fossil accumulations. The shells resemble those of anthracosiids and are herein assigned to Palaeanodonta sp. aff. P. dubia, a species also found in the Permian succession of the Karoo Basin, South Africa. Our results confirm that (a) the true distributions in space and time of all Permian non-marine (freshwater) bivalves are not yet well known, and (b) there is no evidence for marine conditions in the upper part of the Brenton Loch Formation.

NEW FOSSIL RECORDS OF PLEISTOCENE MARINE MOLLUSKS IN SOUTHERN BRAZIL

Fossils of the gastropods Diodora patagonica, Zidona dufresnei, Olivancillaria carcellesi, Lamniconus lemniscatus carcellesi and the bivalve Arcinella brasiliana are registered for the first time from the outcrops of Chui Creek, on the coastal plain of Rio Grande do Sul State, southernmost Brazil, together with other taxa previously known elsewhere. The specimens were collected in a shallow Pleistocene marine facies exposed at the base of the banks of the creek, in a fossil concentration possibly formed by storm events. The taxa described here live in shallow environments (with the exception of A. brasiliana and Z. dufresnei) with sandy bottoms (except for D. patagonica, T patagonica, B. odites, C. rhizophorae and A. brasiliana). The presence of L. lemniscatus carcellesi, found living today only in Uruguay and Argentina, indicates a wider distribution for this taxon during the late Pleistocene.

Production of Excirolana armata (Dana, 1853) (Isopoda, Cirolanidae) on an exposed sandy beach in southeastern Brazil

The somatic and gonad productions of the cirolanid isopod Excirolana armata were analyzed by taking monthly samples from December 2003 to November 2005 on Una beach, So Paulo state (24A degrees S), southeastern Brazil. Sampling was performed along three fixed transects established from the base of the foredunes to the waterline. Weight-specific growth rate was used to estimate the E. armata somatic production for 2004 and 2005, separately. The gonad production was estimated based on the monthly reproductive potential (mean number of eggs/embryos per female x monthly abundance of ovigerous females with near-release broods) for 2004. The annual somatic production of E. armata population varied from 15.57 to 17.25 g AFDW m(-1) year(-1) and the somatic production/biomass ratio (P (s)/B) from 3.55 to 3.14 year(-1) for 2004 and 2005, respectively. The P (s)/B ratios were higher for males (4.02 and 3.19 year(-1) for 2004 and 2005) than for females (3.10 year(-1) for both years). The annual gonad production (P (g) = 1.07 g AFDW m(-1) year(-1)) contributed about 15 and 6% to the total production (P (s) + P (g)) of females and the population, respectively. The proportion of gonad to somatic production of females (P (g)/P (s)) increased with individual size (ca 90% in the 7.5 mm size class), and the annual weight-specific gonad production (P (g)/B ratio) was estimated to 0.24 year(-1). The high P (s)/B ratios estimated for E. armata derive from the fast growth of individuals and show the importance of this population to the energy flow on Una beach ecosystem. However, the low percentage of juveniles verified in this population and in other studies of populations of the genus Excirolana is discussed as an important source of underestimation of P (s)/B ratio.

Mechanism of colonization in the Mediterranean-sea. Asperarca nodulosa: morphological and genetic analysis

Il mar Mediterraneo è un bacino acquifero peculiare per la recente colonizzazione di specie aliene, per l’evento geologico legato alla Crisi di salinità del Messiniano e per l’ampio range di salinità. L’individuazione dei meccanismi di colonizzazione si è incentrata sullo studio morfologico, istologico e molecolare delle specie Asperarca nodulosa ed Anadara demiri (Arcidae-Bivalvia-Mollusca). La ricerca si è basata sulla caratterizzazione morfologica, con utilizzo del microscopio elettronico a scansione, al fine di individuare il tipo di sviluppo larvale. Successivamente i dati rilevati al S.E.M. sono stati supportati dall’indagine istologica che ha evidenziato la presenza di gonadi a sessi distinti e la non incubazione larvale. L’ulteriore analisi filogenetica ha permesso di evidenziare la netta suddivisione tra le tre popolazioni studiate, indagine effettuata tramite marcatori arbitrari (RAPDs) e nucleari specifici (ITS). I risultati ottenuti trovano supporto da quanto noto su base morfologica. I dati, nel complesso, mostrano una perdita delle capacità di diffusione della specie tramite sviluppo larvale plantotrofico a favore di quello lecitotrofico o diretto; tale tesi è ulteriormente supportata dai dati molecolari che mostrano una netta separazione delle popolazioni prese in esame ed un conseguente isolamento tra individui appartenenti a zone di profondità del Mediterraneo (sub-bacini abissali). La ricerca ha, inoltre,esaminato i meccanismi di introduzione attuali nel bacino acquifero che è soggetto ad una nuova invasione da parte specie aliene dovuta all’apertura del canale di Suez. L’analisi si è focalizzata sullo studio per l’ individuazione dell’origine della specie aliena A. demiri , di presunta derivazione Indo-Pacifica, ma rivelatasi, nei dati preliminari, di origine Atlantica.

A molecular phylogeny of bivalve mollusks: ancient radiations and divergences as revealed by mitochondrial genes

The main scope of my PhD is the reconstruction of the large-scale bivalve phylogeny on the basis of four mitochondrial genes, with samples taken from all major groups of the class. To my knowledge, it is the first attempt of such a breadth in Bivalvia. I decided to focus on both ribosomal and protein coding DNA sequences (two ribosomal encoding genes -12s and 16s -, and two protein coding ones - cytochrome c oxidase I and cytochrome b), since either bibliography and my preliminary results confirmed the importance of combined gene signals in improving evolutionary pathways of the group. Moreover, I wanted to propose a methodological pipeline that proved to be useful to obtain robust results in bivalves phylogeny. Actually, best-performing taxon sampling and alignment strategies were tested, and several data partitioning and molecular evolution models were analyzed, thus demonstrating the importance of molding and implementing non-trivial evolutionary models. In the line of a more rigorous approach to data analysis, I also proposed a new method to assess taxon sampling, by developing Clarke and Warwick statistics: taxon sampling is a major concern in phylogenetic studies, and incomplete, biased, or improper taxon assemblies can lead to misleading results in reconstructing evolutionary trees. Theoretical methods are already available to optimize taxon choice in phylogenetic analyses, but most involve some knowledge about genetic relationships of the group of interest, or even a well-established phylogeny itself; these data are not always available in general phylogenetic applications. The method I proposed measures the "phylogenetic representativeness" of a given sample or set of samples and it is based entirely on the pre-existing available taxonomy of the ingroup, which is commonly known to investigators. Moreover, it also accounts for instability and discordance in taxonomies. A Python-based script suite, called PhyRe, has been developed to implement all analyses.