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D. 2004. Organic enrichment and structure of the macrozoobenthic community in the northern Adriatic Sea in an area facing Adige and Po mouths. e ICES Journal of Marine Science, 61: 871e881.The structure of the macrozoobenthic community and the vertical distribution of organisms in the sediment were studied in order to assess the effects of river outflows and organic enrichment on the benthic community of the North Adriatic Sea. Sampling was carried out at one offshore sandy station (S3) and at two coastal muddy stations (S1 and S2), near to river Po and Adige deltas. Samples were collected in four surveys covering one year from April 1995 to January 1996. In all surveys, the offshore sandy station showed a complex trophic structure, high species richness and diversity, with the occurrence of tubicolous or burrowing polychaetes like Nothria conchylega, Aponuphis bilineata, Maldane sarsi, Nematonereis unicornis and Eunice vittata, which also colonized the deeper sediment layers. On the other hand, the coastal muddy stations both exhibited similar species composition and a great abundance of dominant, opportunistic species such as the bivalve Corbula gibba, typical of unstable sea bottoms with a high rate of sedimentation, and some polychaetes typical of sublittoral muddy bottoms such as Levinsenia gracilis, Aricidea claudiae, Prionospio malmgreni, Sternaspis scutata and P. cirrifera. The high density of a few opportunistic species (mainly surface-deposit feeders) and the scant penetration of organisms within sediments that characterized the stations S1 and S2 support other evidence of the eutrophication of the coastal areas of the north-western Adriatic Sea. However, the high biomass values, the species richness and diversity observed in S1 and S2 suggest the occurrence of less extreme conditions than at other highly-eutrophicated coastal areas. River outflows, eutrophication and, especially, the increasing frequency of acute dystrophic events may be recognized as the driving forces determining the structure and composition of the macrozoobenthic community at coastal areas of north-western Adriatic Sea.

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The holocentric mitotic chromosomes of Megoura viciae, a species that has been little studied cytogenetically to date, have been characterized by applying G, C, AluI, and HaeIII banding techniques. C bands have shown the best defined patterns, particularly on the X chromosome. This chromosome, on the other hand, behaved as the most reactive to the various treatments. Uncondensed, prometaphase X chromosomes showed a number of heterochromatic bands, interspersed among the euchromatin, which fused together during metaphase condensation. AluI and HaeIII treatments also produced reproducible banding patterns. These data permit an accurate identification of the X chromosome as well as of the autosomal pairs 1 and 2, and facilitate the construction of nonambiguous karyotypes. They will also stimulate studies on the organization of chromatin in holocentric, holokinetic chromosomes. Finally they could also promote research on chromosomal rearrangements that have occurred during the course of speciation and evolution of aphids, since these kinds of events may be significantly affected by the condition of chromosomal holocentrism.Key words: aphids, holocentric chromosomes, chromosome banding, heterochromatin.

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