A critical update of Mediterranean chitons (Mollusca: Polyplacophora) with the description of new taxa.

The Mediterranean Sea houses a rather diverse chiton fauna (Mollusca: Polyplacophora). Four are here described as new, all based upon loose valves recovered from biogenic sediments: Leptochiton freiwaldi sp. nov., Hanleya schwabei sp. nov., "Ischnochiton" luquei sp. nov., Acanthochitona barbarae sp. nov. The updated Mediterranean Sea chiton fauna comprehends as many as 47 species, distributed in the families Leptochitonidae (15 species), Hanleyidae (3 species), Ischnochitonidae (7 species), Callistoplacidae (1 species), Chaetopleuridae (1 species), Callochitonidae (3 species), Chitonidae (5 species), Lepidochitonidae (6 species), Tonicellidae (1 species), Acanthochitonidae (5 species). Seven taxa are only known from loose valves: Leptochiton antondohrni, L. freiwaldi sp. nov., Hanleya schwabei sp. nov., "Ischnochiton" luquei sp. nov., Lepidochitona marcoi, Boreochiton ruber and Acanthochitona barbarae sp. nov. Similarly to other deep-sea mollusks described from the Mediterranean basin, some of them could possibly belong to last glacial Pleistocene submerged assemblages. On the contrary, Hanleya schwabei sp. nov. and Acanthochitona barbarae sp. nov. occur also at shallower depths, and are assigned to the modern Mediterranean fauna. The presence of the Atlantic taxon Chaetopleura angulata could be an accidental introduction into the Mediterranean. The species Tegulaplax hululensis, considered a Lessepsian immigrant, is a potentially forerunner of a more massive introduction of tropical Polyplacophora via the Red Sea. This study set a baseline for a better understanding of the evolutionary and biogeographic patterns of the Mediterranean Polyplacophora.