On the taxonomy of three sympatric sibling species of the Brachionus plicatilis (Rotifera) complex from Spain, with the description of B-ibericus n. sp.

The accumulation of evidence during the last decade led to the splitting of the Brachionus plicatilis complex (Rotifera) into two morphologically recognizable species: B. plicatilis Muller and B. rotundiformis Tschugunoff, previously referred to as L- and S-type B. plicatilis (s.l.), respectively. However, recent population genetics and molecular studies have revealed that each of these taxa concern cryptic species complexes. In particular, in Torreblanca Marsh, a wetland on the Mediterranean coast of Spain, three genetically distinct groups in this rotifer complex have been shown to co-occur. Differences in genetic markers, ecological preferences, mixis responses, mating behaviour and no evidence of gene flow between them have led to the conclusion that they must be considered as three different biological species. In this study we present a detailed comparative analysis using light and scanning electron microscopy of laboratory strains enabling a morphological characterization of the three species. Fine morphology and morphometry revealed taxonomic characters constant enough to recognize three well-defined morphologies, which always correspond with the respective biological species identified. Since no type material of both B. plicatilis and B. rotundiformis is available, we designed our Spanish clones as neotypes, which would allow further comparative work. Furthermore, B. ibericus n. sp. is described. This study sets the first step for a complete characterization of the biological diversity contained within this economically important species complex.