Aggregation of sponge cells: the aggregation factor as a tool to establish species

Abstract

A description of a new species Thoosa istriaca of Porifera (Demospongia: Clionidae) from the North Adriatic is given. Characterization is based on both spiculation and the aggregation behavior of its cells. The characteristic spiculation of T. istriaca are its megascleres (tylostyles, subtylostyles and oxeas) and microscleres (spirasteres and oxyasters), the main being the oxyasters, featured by six equal rays which radiate from a central point. Aggregation factors have been isolated from the new species and from its closely relative T. mollis Volz. These aggregation factors are absolutely species-specific for the aggregation process of dissociated single cells of the two sponge species; heterotypic aggregation does not occur. This finding provides, at least in some cases, a new tool to establish sponge species on a biochemical or cytological level.