Mactridae

Abstract: The nuclear DNA content (2 C value) of 200 individuals representing 10 species of bivalve molluscs belonging to the families Pectinidae (Chlamys opercularis and Pecten maximus), Ostreidae (Ostrea edulis), Mytilidae (Mytilus edulis and M. galloprovincialis), Mactridae (Spisula solidissima), Cardiidae (Cerastoderma edule), and Veneridae (Venerupis rhomboideus, V. pullastra, and Ruditapes decussatus) have been analyzed by measuring the fluorescent signal of ethidium bromidestained gill cells using flow cytometry Mean genome sizes ranged from 2.23 pg per diploid nucleus in Chlamys opercularis to 3.84 pg in M. galloprovincialis. The distribution of DNA values among all species was continuous and overlapping. There was significant heterogeneity in mean genome size between individuals within species as well as among the different species. A high per cent of the total genome size-variation was allocated at the species level (92%), and 7% at the level of individuals within species. The data suggest that a significant fraction of the bivalve genome, on average ≃0.17 pg or 7%, is free to vary among individuals of the same species without phenotypic or biological consequence. The correlation between the 2 C value and chromosome number was low, suggesting some variation in the amount of DNA per chromosome. Within the subclass Pteriomorphia, the species of Pectinidae, Ostreidae and Mytilidae have shown high genome size-differences correlating with their evolutionary distance.

Abstract: Ecological aspects of 75 megabenthic bivalve species found on the south coast of Portugal (from Vila Real to Sagres) were studied based on the information provided by seasonal bivalve surveys from 2000 to 2007 (8600 hauls, simultaneously using a razor shell dredge and a clam dredge). Of the 75 species identified, 36 occurred less than 30 times, and thus were considered rare in the area. The remaining 39 bivalves were analysed according to their occurrence, bathymetric distribution, geographic preferences, seasonal preferences, burying-depth, beach exposure and river mouth proximity. All species belonging to the Pharidae and Solenidae families (razor shells) and most Tellinidae were significantly more frequent in the razor shell dredge (indicating deeper burying in the sediment), whilst the families Cardiidae and Donacidae were significantly more frequent in the clam dredge (indicating that these species are probably closer to the sediment surface). As for the season, most bivalve species occurred similarly in both seasons (19 sp; 49%), but a large proportion were more abundant during the autumn surveys (17 sp., 44%), whereas only three species were commoner during the spring surveys. Most species belonging to the families Cardiidae and Mactridae were commoner in the autumn surveys. The spatial distribution differed between species and cluster analysis identified four communities with greater geographic affinity. Species belonging to the family Cardiidae were preferably found in the western part (WB) and the eastern part (S) of the study area, whereas the families Donacidae, Mactridae and Tellinidae occurred mainly in the central area (EB) and the eastern (S) coastal sectors. Overall, shallower species (modal depth at 3-6 m) showed greater occurrences and abundances than the deeper ones, and the depth pattern observed did not change between seasons. Donacidae and Mactridae (except Mactra glauca ) were represented essentially by shallow species, whereas Cardiidae (except Acanthocardia tuberculata and Cerastoderma edule ) included mostly species occurring in deeper waters. Bathymetric sequence of species distribution within some families was observed.

Abstract: A molecular DNA probe was developed for identification of larvae of the commercial surfclam Spisula solidissima (family Mactridae), to distinguish early-stage veligers from larvae of other common bivalve species in a study of surfclam settlement and recruitment on the New Jersey continental shelf. For discrimination of S. solidissima from other common bivalve species at the study site (almost all of which belong to different families), an oligonucleotide designed from the nucleotide sequence of the 18S ribosomal RNA gene provides a useful and sensitive family-specific probe and primer. For discrimination between S. solidissima and Mulinia lateralis (both members of Mactridae), the 18S rRNA gene was examined by restriction fragment length polymorphism (RFLP) analysis. A combination of the DNA probe and RFLP analysis provides a positive identification of S. solidissima and M. lateralis larvae in coastal plankton samples.

Abstract: The 18S rRNA gene from three scallop species (Placopecten magellanicus, Chlamys islandica, Argopecten irradians) and 7 mactrid clam species (Spisula solida, S. subtruncata, S. solidissima, Mactromeris polynyma, Tresus nuttallii, T. capax, Mulinia lateralis) have been fully sequenced. Phylogenetic analyses have supported the scheme of Waller (1991) for the Pectinidae but conflict with current evolutionary concepts and classification within the Mactridae. The Mactridae are shown to have evolved monophyletically. The current subfamilial position of Mactromeris, and the subgenera Spisula and Hemimactra of the genus Spisula, are not supported by this data.