Cusps and pipis on a sandy ocean beach in New South Wales

The effect of small-scale variation in beach morphology has been largely ignored in studies of beach macrofauna. This study examined the distribution and abundance of the large bivalve, Donax deltoides (commonly known as the ‘pipi’) in relation to beach cusps (rhythmically spaced undulations of the beachface consisting of scalloped bays and flanking horns on a scale of tens of metres). No differences were found in the abundance of pipis downshore of cusp horns versus cusp bays at any of three sites. In contrast, previous work on a relatively low-energy (reflective) beach reported greater abundances of bivalves below cusp bays than below cusp horns. Results suggest that the swash climate on the higher-energy (more dissipative) beach studied here produces weaker cusping and weaker patterns in the active or passive redistribution of beach fauna by swash action. Wider more dissipative beaches also allow beach macrofauna to remain on flatter parts of the beach, further below cusps than on reflective beaches. The more rigorous study design used here may also contribute to the difference in results between this study and previous studies. However, populations of pipis below cusp bays did contain a greater proportion of small individuals (≤20 mm length) than populations on cusp horns, suggesting some effect related to beach cusps. Small pipis live closer to the beach surface as they have shorter siphons and are subject to larger rates of dislodgement and movement from cusp horns to cusp bays by swash action than are large pipis. Future ecological studies of beaches with cusps should take beach cusps and the processes producing them into account as they may affect the distribution, abundance and the size distribution of beach invertebrates.     

Fabricational morphology of oblique ribs in bivalves

Most analyses on allometry of long bones in terrestrial mammals have focused on dimensional allometry, relating external bone measurements either to each other or to body mass. In this article, an analysis of long bone mass to body mass in 64 different species of mammals, spanning three orders of magnitude in body mass, is presented. As previously reported from analyses on total skeletal mass to body mass in terrestrial vertebrates, the masses of most appendicular bones scale with significant positive allometry. These include the pectoral and pelvic girdles, humerus, radius+ulna, and forelimb. Total hindlimb mass and the masses of individual hindlimb bones (femur, tibia, and metatarsus) scale isometrically. Metapodial mass correlates more poorly with body mass than the girdles or any of the long bones. Metapodial mass probably reflects locomotor behavior to a greater extent than do the long bones. Long bone mass in small mammals (<50 kg) scales with significantly greater positive allometry than bone mass in large (>50 kg) mammals, probably because of the proportionally shorter long bones of large mammals as a means of preserving resistance to bending forces at large body sizes. The positive allometric scaling of the skeleton in terrestrial animals has implications for the maximal size attainable, and it is possible that the largest sauropod dinosaurs approached this limit.     

Some aspects of water filtering activity of filter-feeders

On the basis of the previous publications, our new data and the existing scientific literature, we have formulated some fundamental principles that characterize the pivotal roles of the biodiversity of filter-feeders in ecosystems. Among those roles are: (1) the role of ecological repair of water quality, (2) the role of contributing to reliability and stability of the functioning of the ecosystem, (3) the role of contributing to creation of habitat heterogeneity, (4) the role of contributing to acceleration of migration of chemical elements. It is an important feature of the biomachinery of filter-feeders that it removes from water various particles of a very broad range of sizes. Another important principle is that the amount of the organic matter filtered out of water is larger than the amount assimilated so that a significant part of the removed material serves no useful function to the organism of the filter-feeder, but serves a beneficial function to some other species and to the ecosystem as a whole. The new experiments by the author additionally demonstrated a vulnerability of the filtration activity of filter feeders (e.g., bivalves and rotifers) to some xenobiotics (tetradecyltrymethylammonium bromide, heavy metals and some others). The inhibition of the filtration activity of filter-feeders may lead to the situation previously described as that of an ecological bomb of the second type.     

Plasticity in resource allocation based life history traits in the Pacific oyster, Crassostrea gigas. I. Spatial variation in food abundance

We investigated the quantitative genetics of plasticity in resource allocation between survival, growth and reproductive effort in Crassostrea gigas when food abundance varies spatially. Resource allocation shifted from survival to growth and reproductive effort as food abundance increased. An optimality model suggests that this plastic shift may be adaptive. Reproductive effort plasticity and mean survival were highly heritable, whereas for growth, both mean and plasticity had low heritability. The genetic correlations between reproductive effort and both survival and growth were negative in poor treatments, suggesting trade-offs, but positive in rich ones. These sign reversals may reflect genetic variability in resource acquisition, which would only be expressed when food is abundant. Finally, we found positive genetic correlations between reproductive effort plasticity and both growth and survival means. The latter may reflect adaptation of C. gigas to differential sensitivity of fitness to survival, such that genetic variability in survival mean might support genetic variability in reproductive effort plasticity.     

一个值得注意的修订--评"中国黑龙江省东部早白垩世双壳类"

1997年,顾知微、李子舜、于希汉(Gu et al.,1997)发表了英文专著"中国黑龙江省东部早白恶世双壳类"("Lower Cretaceous bivalves from the eastern Heilongjiang province of China").他们将前人记述为侏罗纪的黑龙江省东部龙爪沟和鸡西群的双壳类修改为早白恶世分子,并将长期被认为属中-晚侏罗世,或晚侏罗世-早白恶世早期的热河群的时代确定为早白恶世.这一重要的修订,非常值得地质古生物工作者注意.     

Anthropogenic Pressure on a Molluscan–Trematode Community over a Long-term Period in the Basingstoke Canal, UK, and Its Implications for Ecosystem Health

A long-term study of a molluscan–trematode community in the Basingstoke Canal, UK, was undertaken over the period 1970–2003 which coincided with a significant restoration program involving substantial anthropogenic changes to the canal’s ecosystem. The aim of this study was to correlate these changes with alterations in the molluscan–trematode community, focusing on fluctuations in the prevalence and species richness of the trematode population as a good indicator, in terms of biodiversity, of ecosystem health. Molluscs were sampled at four time periods (1970, 1982, 1983, 2003) and examined for trematode parasites. The molluscan population over the sampling period demonstrated a limited stability with few species being present during all time periods. During 1982 and 1983, when restoration of the sampling site was being undertaken, Lymnaea stagnalis dominated the molluscan fauna, possibly because it was best able to take advantage of the disturbed conditions, while other species such as Bithynia tentaculata were absent. In the trematode population, the prevalence and diversity of both cercarial and metacercarial infections was high in 1970 prior to the period of restoration work. However, during 1982 and 1983, the trematode community was significantly reduced with cercarial prevalence declining to less than 1%. By 2003, more than 12 years after restoration had been completed, the trematode population had shown only a modest recovery. Trematodes use a wide range of different host species for completing their life-cycles and may be used as bioindicators of ecosystem diversity and health. An interpretation of the structure of the molluscan–trematode community over the sampling period suggests that the restoration project had an initial negative effect on ecosystem health, in terms of biodiversity, but this has subsequently only shown modest signs of recovery suggesting continuing problems in ecological functioning and stability.     

Biostratigraphie des brachiopodes et âge carixien (Pliensbachien inférieur) des calcaires à grands bivalves en Algérie occidentale

Recent researches on the Lower Jurassic of Western Algeria allow to establish a lithostratigraphic standard correlating the different members and formations developed in the Ouarsenis and Tlemcen Mountains, the Oran High Plains, the Nador and Ksour Mountains. The position of the large bivalve limestones (= Lithiotis limestones) is well established in the different lithologic successions. This facies is widespread in Western Algeria where it is interbedded with brachiopod marker beds, indicating short periods of maximum flooding. The large number of collected brachiopods are distributed into four “faunas” (assemblages) ranging from the Late Sinemurian (= Lotharingian) to the Early Pliensbachian (= Carixian). These faunas have been dated by the age of the species that they have in common with the NW european and western tethyan provinces. These chronological data are confirmed by rare ammonites. All these results evidence the age of the large bivalve facies in Western Algeria. They are contained in the Middle to Late Carixian (Demonense and Dilectum Zones). This datation is in conformity with that known from the Eastern High-Atlas (Bou Dahar). Consequently, the large bivalves cannot be considered as “markers for the unique Domerian” as it has been too often asserted. The palaeontological part of our study shows that the multicostate Zeilleriids (several Tauromenia species from the Late Sinemurian to the Early Carixian) are older than the multicostate Terebratulids (Hesperithyris species from the Middle to Late Carixian).     

Seasonal Morphological Changes in the Intestinal Digestive Epithelium of the Mussel Crenomytilus grayanus

Seasonal morphological changes in the intestinal digestive epithelium of the mussel Crenomytilus grayanus (Dunker) were studied. No changes in the cellular composition of the lining epithelium of the intestine were revealed during the annual cycle. Cyclic morphofunctional changes, including reduction of the height of the epithelium in summer and its hypertrophy in winter, increase in the number and size of the nucleoli, etc., were shown to occur.     

Comparative mitochondrial genomic analyses of three chemosynthetic vesicomyid clams from deep‐sea habitats

Vesicomyid clams of the subfamily Pliocardinae are among the dominant chemosymbiotic bivalves found in sulfide‐rich deep‐sea habitats. Plastic morphologies and present molecular data could not resolve taxonomic uncertainties. The complete mitochondrial (mt) genomes will provide more data for comparative studies on molecular phylogeny and systematics of this taxonomically uncertain group, and help to clarify generic classifications. In this study, we analyze the features and evolutionary dynamics of mt genomes from three Archivesica species (Archivesica sp., Ar. gigas and Ar. pacifica) pertaining to subfamily Pliocardinae. Sequence coverage is nearly complete for the three newly sequenced mt genomes, with only the control region and some tRNA genes missing. Gene content, base composition, and codon usage are highly conserved in these pliocardiin species. Comparative analysis revealed the vesicomyid have a relatively lower ratio of Ka/Ks, and all 13 protein‐coding genes (PGCs) are under strong purifying selection with a ratio of Ka/Ks far lower than one. Minimal changes in gene arrangement among vesicomyid species are due to the translocation trnaG in Isorropodon fossajaponicum. Additional tRNA genes were detected between trnaG and nad2 in Abyssogena mariana (trnaL3), Ab. phaseoliformis (trnaS3), and Phreagena okutanii (trnaM2), and display high similarity to other pliocardiin sequences at the same location. Single base insertion in multiple sites of this location could result in new tRNA genes, suggesting a possible tRNA arising from nongeneic sequence. Phylogenetic analysis based on 12 PCGs (excluding atp8) supports the monophyly of Pliocardiinae. These nearly complete mitogenomes provide relevant data for further comparative studies on molecular phylogeny and systematics of this taxonomically uncertain group of chemosymbiotic bivalves.     

Opisoma excavatum Boehm,a Lower Jurassic photosymbiotic alatoform‐chambered bivalve

Alatoform bivalves are a polyphyletic group characterized by antero‐posteriorly compressed shells and a ventro‐lateral wing originating from a tight fold of the shell wall. This bizarre shell morphology is interpreted as an adaptation for algal photosymbiosis in heliophilous bivalves. The group contains the living heart cockle Corculum together with four extinct genera ranging in age from the Permian to the Jurassic. The Jurassic alatoform bivalve is Opisoma, which has an aragonitic shell that is divided into two regions, both with different functions: one for stabilization, the other for hosting symbionts. The dorsal part of the shell is massive and played the stabilization role. The ventral part has a very thin and fragile shell that permitted the transmission of light into the internal tissues harbouring photosymbionts. The morphology of this delicate ventral part has thus far remained obscure, due to lack of preservation. Accumulations of Opisoma excavatum Boehm with exquisitely preserved shells containing the fragile winged ventral parts are common within the Pliensbachian shallow‐water, lagoonal carbonate succession of the Rotzo Formation of northern Italy. The wings have internal curved chambers limited by septa parallel to the wing edge. The shell of the ventral part consists of irregular fibrous prismatic and homogeneous structures which progressively infill the chambers. As the chambered wings are analogous structures among alatoform bivalves, they are no longer considered a taxonomic character. According to the observed shell orientation in the field and the consequent organization of the soft parts, Opisoma had an opisthogyrate shell.