Taxonomy of Plakina (Porifera: Homoscleromorpha) from Aegean submarine caves, with descriptions of three new species and new characters for the genus

Abstract

Sponges of the Class Homoscleromorpha, despite their high evolutionary significance, are still poorly known due to their small size and cryptic habit. In this study, we describe five species of the homoscleromorph genus Plakina from submarine caves in the Aegean Sea (Lesvos Island, Greece): Plakina bowerbanki, P. trilopha, P. anisoactina sp. nov., P. anomala sp. nov., and P. hellenica sp. nov. Plakina anomala sp. nov. is the first species of the genus with papillae and the first Homoscleromorpha with a microcavity-filling habit. Plakina bowerbanki, P. anomala sp. nov. and P. anisoactina sp. nov. present exceptionally stout, annulated lophose spicules with highly variable ramification patterns, including some original types. The high diversity of Plakina in the two caves of Lesvos Island is similar to that of northwestern Mediterranean caves. Despite being much less studied, the Aegean Sea now equals the Western Mediterranean as the two ecoregions of the Mediterranean with the highest diversity of Plakina, with eight species each. The Aegean Sea encompasses a huge number of submarine caves, and therefore it has great potential for the discovery of new species of Homoscleromorpha.