Abstract
Knowledge of the Haplosyllis species in the Saudi Arabian Red Sea is rather limited, since the so-called cosmopolitan Haplosyllis spongicola and Haplosyllis djiboutiensis apparently present all along the region are the only reported species. However, both are revealed to be species-complexes, the former mostly composed of European species and the later distributed in the Indo-Pacific area. Recently, several new species have been described following more comprehensive taxonomic studies in the respective areas. Haplosyllis leylae sp. nov. can be framed within the "djiboutiensis" complex. The new species, which is herein fully described and illustrated, can be clearly distinguished by the combined presence of numerous small dorsal granules, the low number of articles on each dorsal cirrus, and the chaetal morphology. A dichotomous key of the Indo-Pacific species of Haplosyllis and new information on Haplosyllis eldagainoae are also included.