Marine Biodiversity and Geographic Distributions Are Independent on Large Scales

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Clypeasteroid echinoid tests as benthic islands for gastrochaenid bivalve colonization: evidence from the Middle Miocene of Tarragona,north‐east Spain

Abstract: Middle Miocene tests of Clypeaster from L’Arrabassada (Tarragona, north‐east Spain) show evidence of intense endoskeletozoan colonization, preserved as borings and associated carbonate secretions that allow gastrochaenid bivalves to be identified as the colonizers. Two modes of occurrence have been recognized for these bivalve dwelling cavities; ‘intrastereom clavate borings’ which are restricted to the echinoid stereom, and ‘semi‐endoskeletal dwellings’, which penetrate across the test wall and extend as carbonate crypts into the sediment fill of the internal test cavity. Their size, density and position rule out a syn‐vivo relationship with the echinoids and demonstrate that colonization was post mortem. Because of the endurance of clypeasteroid skeleton and the pronounced bell‐shaped morphology of Clypeaster, the tests of these echinoids provided the most suitable substrates for hard‐bottom colonizers on an otherwise sandy seafloor. The scenario described from Tarragona can be extended to other Neogene and Quaternary strata elsewhere; there is ample evidence for the long‐term utilization of tests of Clypeaster by gastrochaenid bivalves in shoreface palaeoenvironments.     

Annual gametogenic cycle of the freshwater pearl mussel,Lamellidens marginalis (Lamarck, 1819) collected from a perennial lentic habitat of Bangladesh

ABSTRACT

We investigated the annual gametogenic phenology of the freshwater pearl mussel, Lamellidens marginalis (Lamarck, 1819), collected from a lentic habitat at Mymensingh, Bangladesh, using biometry and histology through monthly sampling from August 2015 to July 2016. After biometric measurements, thin slices of dorso-ventral sections were cut from the middle of the mussels for histology to determine sex and level of gonadal maturation. The condition index (CI) ranged from 0.64 (March) to 0.99 (January) over the study period. The CI peaked three times (January, April and July) indicating that the mussels were ripe during these months and subsequent decreases in CI indicated spawning, which was consistent with histology. Both males and females exhibited similar patterns in terms of gonadal development, maturation and spawning activity. It was confirmed that natural populations of L. marginalis spawn throughout the year with remarkable temporal variations, except during December when the surface water temperature reaches annual minima (16.5°C). Highest spawning activity of L. marginalis was noted during February–March, May and July–November. The data obtained in the present study could be useful for the conservation managers of this commercial species by allowing harvesting of better quality mussels to be timed without interrupting major spawning activity.     

Non‐native species have multiple abundance–impact curves

The abundance–impact curve is helpful for understanding and managing the impacts of non‐native species. Abundance–impact curves can have a wide range of shapes (e.g., linear, threshold, sigmoid), each with its own implications for scientific understanding and management. Sometimes, the abundance–impact curve has been viewed as a property of the species, with a single curve for a species. I argue that the abundance–impact curve is determined jointly by a non‐native species and the ecosystem it invades, so that a species may have multiple abundance–impact curves. Models of the impacts of the invasive mussel Dreissena show how a single species can have multiple, noninterchangeable abundance–impact curves. To the extent that ecosystem characteristics determine the abundance–impact curve, abundance–impact curves based on horizontal designs (space‐for‐time substitution) may be misleading and should be used with great caution, it at all. It is important for scientists and managers to correctly specify the abundance–impact curve when considering the impacts of non‐native species. Diverting attention from the invading species to the invaded ecosystem, and especially to the interaction between species and ecosystem, could improve our understanding of how non‐native species affect ecosystems and reduce uncertainty around the effects of management of populations of non‐native species.     

Comparison of antibacterial activity in the hemolymph of marine bivalves from Galicia (NW Spain)

A screening study of in vitro antibacterial activity was conducted in marine bivalves with economical importance and widespread along the coast of Galicia (NW Spain). Hemocyte lysate supernatant (HLS) and plasma of Mytilus galloprovincialis, Ostrea edulis, Crassostrea gigas, Ruditapes decussatus, Ruditapes philippinarum, and Cerastoderma edule were incubated with Vibrio splendidus and Micrococcus sp. HLS and plasma for all the species demonstrated antibacterial activity, and C. edule had the highest activity per unit of protein in these hemolymph fractions. Significant differences were not found between HLS and plasma activities. Furthermore, antibacterial activity against Micrococcus sp. (Gram-positive) was stronger than against V. splendidus (Gram-negative).     

Evolution of the rudist bivalve Agriopleura Kühn (Radiolitidae,Hippuritida) from the Mediterranean region

The genus Agriopleura (Radiolitidae) is restricted to the Lower Cretaceous of the Mediterranean region, including the Middle East, and this rudist is apparently absent from the New World. Agriopleura underwent a size increase from late Hauterivian to mid‐late Barremian, matching Cope's rule, followed by a Lilliput phase in the early Aptian. The relative development of radial bands increased through time and represents a key evolutionary index. During its evolution, Agriopleura increased in species diversity and expanded geographically onto the European Mediterranean Tethyan margin from the late Hauterivian to Barremian, after which it disappeared from the region (pseudotermination). In the lower Aptian, after a Lazarus gap, the genus reappears in the southern Mediterranean Tethyan margin. Assuming that Archaeoradiolites is the direct descendant of Agriopleura, the disappearance of the genus in the mid‐Aptian was a pseudoextinction and this coincided with a major crisis of shallow carbonate settings and their associated biota. The definition of Agriopleura species is based on a set of qualitative and quantitative external and internal characters. Five species are recognized: three Barremian species, Agriopleura blumenbachi, the type species, A. marticensis and A. carinata; one lower Aptian species A. libanica; and a new species A. sequana restricted to the upper Hauterivian. Principal component analysis is used to test the distinctiveness of the species and the pattern of relationships of some of their key quantitative characters.     

Aragonitic dendritic prismatic shell microstructure in Thracia (Bivalvia,Anomalodesmata)

The shells of most anomalodesmatan bivalves are composed of an outer aragonitic layer of either granular or columnar prismatic microstructure, and an inner layer of nacre. The Thraciidae is one of the few anomalodesmatan families whose members lack nacreous layers. In particular, shells of members of the genus Thracia are exceptional in their possession of a very distinctive but previously unreported microstructure, which we term herein “dendritic prisms.” Dendritic prisms consist of slender fibers of aragonite which radiate perpendicular to, and which stack along, the axis of the prism. Here we used scanning and transmission electron microscopical investigation of the periostracum, mantle, and shells of three species of Thracia to reconstruct the mode of shell calcification and to unravel the crystallography of the dendritic units. The periostracum is composed of an outer dark layer and an inner translucent layer. During the free periostracum phase the dark layer grows at the expense of the translucent layer, but at the position of the shell edge, the translucent layer mineralizes with the units typical of the dendritic prismatic layer. Within each unit, the c‐axis is oriented along the prismatic axis, whereas the a‐axis of aragonite runs parallel to the long axis of the fibers. The six‐rayed alignment of the latter implies that prisms are formed by {110} polycyclically twinned crystals. We conclude that, despite its distinctive appearance, the dendritic prismatic layer of the shell of Thracia spp. is homologous to the outer granular prismatic or prismatic layer of other anomalodesmatans, while the nacreous layer present in most anomalodesmatans has been suppressed.     

中国淡水双壳类特有种的地理分布

通过查阅有关文献整理得出,中国淡水双壳类特有种计有58种,隶属于双壳纲(Bivalvia)2科17属,其中主要是蚌科(Unionidae)的种类(16属57种)。我国淡水双壳类特有种的组成和区系成分,以东洋界华中区的种类占绝对优势,仅有少数种类渗透到古北界;特有种在我国16个省有分布,但主要集中分布于江西、湖南、安徽、浙江、江苏五省。双壳类特有种的形成和保存可能与我国古地理环境及其生活的水域环境有关。     

Quantitative study of a hippuritid rudist lithosome in a Santonian carbonate platform in the southern Central Pyrenees

The Santonian carbonate platform deposits of the Sant Corneli anticline in the southern Central Pyrenees contain distinctive lenticular to tabular lithosomes formed by congregations of slender hippuritid rudists. Here we make a quantitative study of one of the lithosomes in the Sant Pere de Vilanoveta Member, in the northern side of Sant Corneli. It is exposed over some 4 km, along a WNW–ESE section, and shows a remarkably persistent thickness up to a maximum of 5.15 m, though for the most part it is less than 3 m thick. In the lithosome, hippuritid shells are mostly preserved inclined about 30°–60° from the perpendicular with respect to bedding. The majority of inclined shells lean towards the southwestern to southeastern quadrants, the inferred principal downstream direction. Hippuritids are loosely clustered and supported in a fine bioclastic matrix. Percentage cover of hippuritids ranges from 19.8% at the base to 31.9% in the middle and top of the lithosome. The preliminary data on numerical densities (number of individuals per unit area) of hippuritids show some clustering around values of about 290–750 individuals per m². The inclined orientation of hippuritid shells seems original and the result of active growth by the animals. The high numerical density of hippuritids at the base of the lithosome may indicate that the hippuritid congregation grew rapidly. The congregation appears to have reached an optimal level of density by the middle of the lithosome and to have maintained it through time during the development of the rudist congregation. The lithosome lacks relief and has no evidence of any rigid framework.     

Strontium isotope stratigraphy of Cretaceous hippuritid rudist bivalves: rates of morphological change and heterochronic evolution

Strontium isotope stratigraphy of 17 localities of rudist formations in the region of the former Mediterranean Tethys has provided a reliable and precise stratigraphical frame for the evaluation of morphological change in hippuritid rudist bivalves during the Coniacian–Campanian. The phyletic lineage Vaccinites cornuvaccinum (Bronn)–Vaccinites chaperi (Douvillé) evolved from the Early Coniacian until the Early Campanian and is characterized by phyletic size increase and allometric growth, as shown by morphometrical measurements of 102 shells. These chronospecies intergrade in the Late Coniacian so that V. cornuvaccinum is considered to be a reliable marker species for the Coniacian. The taxonomy of Vaccinites alpinus (Douvillé) is discussed and the species is recognized as a senior synonym of Vaccinites ultimus (Milovanovi ). It appears first in the Late Santonian and the last appearance is probably in Late Campanian. Both lineages are characterized by phyletic size increase and peramorphic evolution involving hypermorphosis. A doubling of the length of the mantle margin occurred within 5 m.y. in both lineages. The results demonstrate that the combination of morphometric analyses and stratigraphical precision provides an important tool for the delineation of tempo and mode of evolution in rudist bivalves. Strontium isotope stratigraphy resulted in a considerable revision of the ranges of the species investigated. As the stratigraphy of many Tethyan carbonate platforms relies on the distribution of rudist bivalves, and the species investigated are abundant in many rudist formations, the history of many Late Cretaceous carbonate platforms must be re-evaluated.