The mudsnail genus Hydrobia s.s. in the northern Atlantic and western Mediterranean: a phylogenetic hypothesis

The mudsnail taxon Hydrobia s.l. plays a major role in numerous ecological and parasitological studies. Yet, its taxonomy is confusing and its biogeog raphy is poorly understood. A principal problem is that taxa of Hydrobia s. l. belong to morphostatic radiations - widely allopatric species radiations with little or no habitat diversification and a low level of anatomical ch ange. So far, three morphostatic radiations can be identified within Hydrob ia s.l.: Hydrobia s.s., Peringia, and Ventrosia. These radiations are ident ical with the putative genera of Hydrobia s.l. The purpose of the paper is to infer phylogenetic relationships within one of these radiations, Hydrobi a s.s. in the northern Atlantic and western Mediterranean. A total of 22 po pulations, including topotypical populations of five commonly used taxa, we re studied genetically using partial sequences of the mitochondrial cytochr ome c oxidase subunit I gene. Based on molecular data and the species conce pt we define, the following species and subspecies were identified: Hydrobi a acuta acuta (Draparnaud, 1805) [= H. minoricensis (Paladilhe, 1875)], H. acuta neglecta Muus, 1963, and H. glyca (Servain, 1880) (= H, joossei van A artsen, Menkhorst and Gittenberger, 1984). One population from Djerba, Tuni sia (Hydrobia sp. A) and one population from Mallorca, Spain (Hydrobia sp. B) are genetically distinct from all other taxa studied here. Both populati ons potentially represent new species. Due to the fact that only one popula tion each has been studied, and so the degree of variation within these two taxa cannot be assessed, a final decision regarding their species level ca nnot yet be made.