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SUMMARY: Of the 10 species in the genus Tambja (Polyceratidae) described in the biogeographical Atlantic-Mediterranean subregion, 6 species were chosen for the present study because of their relative abundance in the eastern Atlantic and Mediterranean area. Data are given on the variations in the number of radular tooth rows and their morphology for specimens at different developmental stages from juveniles to adults. Juvenile specimens smaller than 10 mm show a variable number of tooth rows which is always above 20. In juvenile specimens larger than 10 mm in length or the juvenile pre-adult and adult stages, the number of tooth rows is invariably lower than 20, but a positive linear relationship between body length and the number of tooth rows is still shown. The significance of this phenomenon is not known at this time, although different hypotheses have been suggested. especies del géne-ro Tambja (Polyceratidae) descritas en la subregión biogeográfica atlántico-mediterránea hemos seleccionado las 6 que lo han sido en la zona este del Océano Atlántico y en el Mediterráneo, para realizar un estudio ontogenético de la rádula de ejemplares en distintas fases de crecimiento. La recolección del material de estudio ha sido una tarea compleja dada la relativa abundancia de los ejemplares de estas especies, siendo especialmente laboriosa la recolección de ejemplares con una longitud menor de 10 mm. Se ha correlacionado la longitud del animal con el número de filas de dientes en juveniles de muy pequeño tamaño, menores de 10 mm, juveniles preadultos y adultos y se ha estudiado el cambio en la morfología de los dientes en las tres etapas de crecimiento. Destacamos que los juveniles de pequeño tamaño tienen un número de filas de dientes muy elevado, en todos los casos mayor de 20. Los juveniles preadultos y adultos siempre tienen una rádula con menos de 20 filas de dientes. En ejemplares de estas dos últimas fases de crecimiento existe una correlación lineal positiva entre la longitud del cuerpo del animal y el número de filas de dientes. El significado exacto del fenómeno descrito se desconoce por el momento, aunque se exponen distintas hipótesis que pueden dar respuesta al mismo.

This paper discusses the ecology and biogeography of nematodes from freshwater environments, which are extreme in terms of temperature, chemical composition, variability or isolation. The composition of nematode faunas from freshwater pools in bromeliads or tree hollows, hot or mineral springs, pools and bogs in polar regions, seasonal lakes or pools, fresh groundwaters and caves are described and compared. The nematode faunas from these extreme habitats are also compared with those from more typical freshwater environments. Nematodes with evolutionary affinities to freshwaters but found in estuarine sediments are discussed. Conversely, nematodes from freshwaters with evolutionary affinities to otherwise marine taxa are also considered. Common themes in the adaptations of all these nematodes to such unusual environments are synthesized.

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The ionic composition of 38 mineral springs in the province of Granada (Spain), and the distribution of 45 species of nematodes belonging to orders Monhysterida, Araeolaimida, Chromadorida and Enoplida were examined. Water chemistry is used to make two diagrams representing anionic and cationic composition. Diagrams for anionic composition (given the greater variance seen in the springs considered) are used to illustrate the distribution of individual species. The results obtained from species distribution and the correlation between species made it possible to group species which could be associated with springs where each of the anions considered predominated. A greater number of species groups was found to inhabit springs in which chloride concentrations was less than 50% of the total concentration of anions.