A national checklist of marine Mollusca in Spanish waters

A checklist of marine Mollusca recorded in Spanish jurisdictional waters is presented, based on a thorough literature search and a limited input of recent field work. The list is detailed according to the five demarcations of the Marine Strategy Framework Directive (NOR, Spanish north coast; SUR, Spanish coast of the Gulf of Cádiz; ESAL, Strait of Gibraltar and Alboran Sea; LEBA, East coast of Spain and Balearic Islands; CAN, the Canary Islands). The list differentiates coastal species living from the supralittoral zone to the shelf break, deep-sea benthic or demersal species, and holoplanktonic species, and also distinguishes between non-indigenous species and species endemic to a particular demarcation. A total of 2466 marine Mollusca species have been reported from Spanish waters, of which 1126 are recorded only from waters surrounding the Iberian Peninsula, 498 are recorded from the Canaries only, and 842 are shared. That total number represents around 5.5% of the global marine molluscan richness. Shore and shelf species are the most numerous (1837), followed by deep-sea benthic species (490) and pelagic species (139), but the contribution of the deep-sea species is most noteworthy in NOR. All eight molluscan classes were represented, but solenogastres and scaphopods were notably more represented than usual in NOR. Species richness in SUR and ESAL was higher than would be expected from their areas, supporting the claim that Andalusian waters have an exceptionally diverse molluscan fauna. Thirteen species collected from INDEMARES cruises are here reported for the first time in Spanish waters. The species recorded in Spanish seas represent more than half of the 4340 species of Mollusca recorded within the scope of the European Register of Marine Species, making this the highest species count in European seas. The Canary Islands demarcation holds by far the largest number of endemic species (127), but special mention is needed regarding the ca. 20 species endemic to the Strait of Gibraltar, a highly anomalous chorotype in the marine realm. The number of non-indigenous species (38) is surprisingly low compared with that of species known in the Mediterranean Sea, amounting to hardly 1.5% of the total and supporting the view that a high number of native species tends to reduce invasion success. The list is seen as a much needed tool for the identification of priority areas for biodiversity conservation, but requires permanent attention and curating in order