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ABSTRACT. The surface morphology of the ctenidia of Spondylus spinosus Schreibers, 1793 was studied with light and scanning electron microscopy for comparison with the gill structures of other bivalves. The demibranch of S. spinosus is heterorhabdic, with the principal filaments at the descending lamellae and ordinary filaments at the ascending lamellae. The gill lamellae have a prominent gauze-like structure at their distal part, with numerous groups of eight ordinary filaments. They bear ciliary arrays on their frontal surfaces and ostia at their latero-frontal surfaces. Frequent cirral plates form regular interfilamentary junctions. The description of the gill structure of S. spinosus presented here can be used to derive implications for the correlations among the structure, habitat and mode of life of this species. At a particular stage of its adult life, Spondylus spinosus could be used as a subject for biomonitoring studies in natural and experimental environments.

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The general features of the mitotic and meiotic chromosomes analysed in 91 frogs belonging to nine water frog populations distributed in Southwest Anatolia. The differences found in mitotic and meiotic chromosomes revealed the existence of two groups among the populations: the first "Aegean Group" includes those from Izmir, Bulca, Pazaragaç, and the second -"Lake District Group" from Eber, Akşehir, Gelendost, Egirdir, Gölcük, and Beyşehir populations. The major distinction appeared in the number of the rod-shaped bivalents in metaphase I, with only one in the "Aegean Group" compared to one or two in the "Lake District Group". This result indicates a new assemblage among Anatolian water frogs and strengthens the suggestion that the "Lake District Group" that have one or two rod shaped bivalents in metaphase I due to the inclusion of hybrid lineages containing both parental genomes. It is clear that at least two separate species are present in Anatolia; one of them is possibly Rana ridibunda from the north and the second is closer to the Balkan species Rana epeirotica and Rana shqiperica.