Ambiguities in the taxonomic assignment and species delineation of botryllid ascidians from the Israeli Mediterranean and other coastlines

<p>Based on mt<i>COI</i> sequences comparisons, recent studies reassigned the ‘dwarf <i>Botrylloides leachii’</i> from the Levant as <i>Botrylloides nigrum.</i> Here we conducted a survey of the literature and of deposited mt<i>COI</i> sequences of botryllid ascidians, elucidating ambiguities in their taxonomy. We found that the species, dwarf morph of <i>Botrylloides leachii, Botrylloides nigrum, Botryllus aster</i> and <i>Botryllus arenaceus</i> are grouped together on a single molecular taxon. Then, results of three additional markers (18S, 28S, H3) contradicted literature suggestions, revealing minute distances between <i>Botrylloides leachii</i> and the ‘dwarf <i>Botrylloides leachii’</i>. Moreover, only <i>Botrylloides leachii</i> and the ‘dwarf <i>Botrylloides leachii’</i> develop giant ampullae as an allorecognition response. Our results raise the possibility that inadequate identification, together with faults in molecular assignment, including queries regarding the efficacy of the mt<i>COI</i> as the exclusive barcoding tool in botryllid ascidians, is the major culprits responsible for the emerged inconsistencies between the mt<i>COI</i> sequences and traditional taxonomy. Thus, we assign the Levantine dwarf form as <i>Botrylloides</i> aff. <i>leachii</i>.</p>