Tonicia atrata and Chiton cumingsii (Polyplacophora: Chitonidae): first records in European waters.

At present, over 300 species of marine alien Mollusca are reported from the European waters (Streftaris et al. 2005; Zenetos et al. 2010). However, only three alien polyplacophoran have been recorded: Chaetopleura angulata (Spengler, 1797), Acanthopleura gemmata (Blainville, 1825) and Chiton hululensis (E. A. Smith, 1903); the latter is considered as “questionable” (Zenetos et al. 2010). These polyplacophoran constituting about 1% of the alien marine mollusc reported from Europe. Here we present the first record of Tonicia atrata (Sowerby, 1840) and Chiton cumingsii Frembly, 1827 in European waters, constituting the first evidence of their presence outside their native range. Furthermore, we give brief notes on the taxonomy and distribution of T. atrata and C. cumingsii, and discuss the potential pathways for introduction to Europe. In Europe, T. atrata occurs together with the well-known alien Ch. angulata; and probably both species have historically been misidentified in collections because both reach large size (> 60 mm) and in many cases the larger size was commonly used to differentiate the presumed alien (Ch. angulata) from the native polyplacophoran of smaller size. Recently in the Bay of Biscay, both species coexist with the Mediterranean Chiton olivaceus Spengler, 1797, which has become a new alien for this region (authors’ pers. obs.). Preserved specimens in the collections of the Department of Biology of Organisms and Systems (Zoology), University of Oviedo, Spain (BOS), previously identified as Ch. angulata from Atlantic coastal waters of the Iberian Peninsula and Canary Islands collected throughout the last decades, were re-examined.