Annotated checklist of Recent Polyplacophora with notes on their systematics

The systematics of chitons is based on morphological and molecular data, which resulted in a well-resolved phylogeny, but the progress in resolving some relationships at the family and genus level has been more limited, and revisionary work is ongoing. A checklist of the 1093 accepted chiton species is presented as a platform containing a list of valid Recent species with their classification. Additionally, it contains comments on systematics and taxa position, with suggestions for possible changes. This form of an annotated catalogue, in this and future editions, allows us to clearly document systematic changes and point out the areas which are still in need of revision. The checklist also includes a section on "phylogenetic systematics", providing updates on taxa whose molecular phylogenies conflict with previous morphological treatments but whose systematics have not yet been formally clarified. We corroborate the position of Choriplax Pilsbry, 1894a and Cryptochiton von Middendorff, 1847a within Mopalioidea. A new family, Nuttallochitonidae fam. nov., is established within Cryptoplacoidea to accommodate Nuttallochiton Plate, 1899. Plaxiphora Gray, 1847a is placed in the reinstated family Plaxiphoridae Iredale, 1915, which is treated here at the superfamily rank as Plaxiphoroidea, based on the existing family-group name. The genus Icoplax Thiele, 1893 is restored to its original taxonomic rank as a separate genus. Another revision clarifies the use of the family Ferreiraellidae Dell'Angelo & Palazzi, 1991 as a substitution of earlier Abyssochitonidae Dell'Angelo & Palazzi, 1989, as there is clear evidence that Ferreiraellidae should be the accepted family name for the species in Ferreiraella.