Redescription of the polychaete Streblospio shrubsolii (Buchanan 1890): morphological and molecular characterization of northern Adriatic populations

During monitoring of benthic biodiversity from the Sacca di Goro (northern Adriatic Sea, Italy), a number of spionid specimens belonging to the genus Streblospio Webster 1879 were collected. While examining these specimens it became clear that they closely resemble S. dekhuyzeni Horst 1909, which in turn was synonymized with Streblospio shrubsolii. However, in the recent redescription of S. shrubsolii several characteristics observed in S. dekhuyzeni are not reported. The phylogenetic reconstruction, based on the mitochondrial cytochrome c oxidase subunit I (COI) gene and the preliminary haplotype study indicate that these specimens belong to the species S. shrubsolii but, also, that they can be ascribed to a distinct haplotype corresponding to a unique morphotype; the existence of such a distinct morphotype can be explained by both climatic and hydrological characteristics of the northern Adriatic lagoons. Specimens belonging to this morphotype differ from the conspecific populations inhabiting other geographical areas and from the most recent and accepted redescription of this species. Morphological characteristics important for differentiation of the morphotype of S. shrubsolii herein described from its conspecifics are discussed, and an updated summary of the main morphological, reproductive and ecological characteristics of S. shrubsolii is provided in order to present a revised and complete description of this species.