Clarification of the taxonomic status of Acanthochitonadiscrepans (Brown, 1827) with new data for the North-East Atlantic Acanthochitona (Polyplacophora, Acanthochitonidae)

Background: The genus Acanthochitona can be easily distinguished from other chitons by having eighteen tufts of bristles on the dorsal side of the densely spiculose girdle. In the North-East Atlantic, five species of this genus have been recognised so far: A.crinita (Pennant, 1777), A.discrepans (Brown, 1827), A.fascicularis (Linnaeus, 1767), A.oblonga Leloup, 1968 and A.pilosa Schmidt-Petersen, Schwabe et Haszprunar, 2015. The nomenclature of A.crinita, A.discrepans and A.fascicularis was confused for a very long time until Kaas (1985) designated type specimens for them and provided a brief key. However, his work lacked detailed descriptions of the three species and some authors doubted that A.discrepans constitutes a separate species. Subsequently, the taxonomic status of A.discrepans has remained unclear.

New information: Here, we implemented an integrative approach which combined morphology and molecular evidence to show that Acanthochitonadiscrepans is, indeed, a valid species and we present re-descriptions for A.crinita, A.discrepans and A.fascicularis.