This research shows the results of an analysis of siliceous spicules found in sediment cores collected in Lake Trasimeno (Umbria, Italy), a shallow lake that experienced an important water level lowering during the last century. A morphological analysis of sedimentary sponge records revealed that the spicules accumulated in the lake sediments over the last 150 years are attributable to Ephydatia fluviatilis, the only sponge species found in the lake in recent years. The stratigraphic analysis of the cores showed that the abundance and size of the sponge spicules (megascleres) have remarkably decreased, suggesting that a significant depletion of the sponge fauna occurred, particularly during the first half of the twentieth century. A correlation analysis has identified morpho-hydrological and related variables (the theoretical fraction of lake surface subjected to resuspension and the amount of total suspended solids) as the most significant factors explaining the change in density of sponge spicules. Two ecological explanations of the sponge decline are proposed, based on the sensitivity of the sponge both to the availability of suitable hard substrata for colonization, and to the amount of wind-resuspended solids. One-ended sigmoid response curves were obtained by regression and corresponding transfer functions were derived, which allow the mean water depth of the lake and total suspended solids to be inferred from spicule density records. The results support the use of sponge spicules as a paleohydrological and paleoecological proxy, application of which appears particularly promising for shallow-water systems.
Black coral colonies belonging to Antipathella subpinnata (Myriopathidae), found in Adriatic Sea (off the Tremiti Islands) and in Tyrrhenian Sea (Mezzo Canale), were inspected with the aim of investigating their reproductive activity. The small colony (about 42 cm tall) from Adriatic Sea was sexually immature, whereas the larger (about 120 cm tall) five colonies from Tyrrhenian Sea were fertile. Four colonies were males and one was a female, thus confirming the gonochoric condition already known for the black coral. Semithin sections proved that most of the egg and sperm masses flow out through the pharynx, even though small gamete masses were also observed emerging from the tentacles. In the female polyps, egg masses were enveloped by parental tissue derived from the breakage of the mesenterial septa, as observed in the male polyps for the sperm cysts masses. Ultrastructural observations provided details on the characteristics of egg and sperm in this taxon. Sperm stood out for the presence of an acrosome-like structure derived from the merging of proacrosomal vesicles. On the whole, the fine organization of the sperm recalled previous descriptions reported for some tropical black coral taxa.
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