The Mysidae (Crustacea: Peracarida: Mysida) in fresh and oligohaline waters of the Mediterranean. Taxonomy, biogeography, and bioinvasion.

A census of Mysidae yielded a total of twelve species plus two non-nominotypical subspecies found so far in fresh and oligohaline waters of the Mediterranean, all belonging to the subfamily Mysinae. Among the nine species in fresh-waters, three are stenoendemics, namely of a single lake (Diamysis lacustris), of two neighbouring river systems (Paramysis kosswigi) or of karstic cave waters (Troglomysis vjetrenicensis). Four species-T. vjetrenicensis, D. lacustris, D. fluviatilis, and Paramysis adriatica sp. nov. described in this paper-are confined to freshwater tributaries of the Adriatic Sea (NE-Mediterranean). This strengthens previous findings about the outstanding role of the Adriatic basin for the endemic diversity of freshwater Mysidae within the Mediterranean. This is possibly related to alternating marine and freshwater-terrestrial phases during the Pliocene-Pleistocene in this semi-enclosed basin. Based on current knowledge, freshwater populations of D. mesohalobia heterandra are also confined to the Adriatic basin; this taxon, however, shows many more populations in brackish waters of the E-Mediterranean and Marmora basins. Two freshwater species (Limnomysis benedeni, Hemimysis anomala) are wide-range invaders of Ponto-Caspian origin, with recent expansion into fresh and brackish waters of the NW-Mediterranean. A further immigrant to this part of the Mediterranean, Neomysis integer, is of NE-Atlantic origin and occurs only marginally in fresh-water.        Five among the nine species found at least once in fresh-water were also reported in oligohaline conditions, mostly also at even higher salinities. A total of eight species plus two subspecies were recorded in oligohaline waters (S = 0.5-5). Among these, only one oligohalobious stenoendemic, Diamysis hebraica, inhabits streams at the Levantine coast.        In the historical biogeographical context, the current distribution of only one out of nine indigenous species in an- to oligohaline waters of the Mediterranean, namely the mainly meso- to polyhalobious Mesopodopsis slabberi, may date back to the early Pliocene flooding of the Mediterranean by Atlantic waters and to later events. For most species, the biogeographical pattern points to a primary origin in the brackish (Miocene) Paratethys; solely the cave-dwelling T. vjetrenicensis has more ancient roots in the Tethyan (Mesogeic) Sea. Both these hypotheses are supported by chorological data and mainly the mineral composition of statoliths. The statoliths are composed of CaCO ₃ as the metastable crystal phase vaterite in nine species plus two subspecies considered versus the otherwise more common CaF ₂ (fluorite) in only three species (or in 7 + 2 versus two Mediterranean indigenes).        All 12 + 2 Mediterranean taxa are figured and described in detail, particularly regarding P. adriatica sp. nov. and the substantially redescribed T. vjetrenicensis Stammer, 1933. Supplementary descriptions are given for P. kosswigi Băcescu, 1948, D. hebraica Almeida Prado-Por, 1981, and N. integer (Leach, 1814). A key to the 14 taxa is given including additional three species of potential future invaders. The tribe Mysini Haworth, 1825, is revised by detachment of the newly defined tribe Paramysini and of the revalidated Hemimysini Czerniavsky, 1882. A key to the resulting six tribes of the subfamily Mysinae is given.