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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 CaCO3 as the metastable crystal phase vaterite in nine species plus two subspecies considered versus the otherwise more common CaF2 (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.

SCUBA diving explorations of three islands off Dumont d'Urville Station at the coast of Adelie Land, East Antarctica, enabled the observation of marine ice caves. Sampling in this unusual habitat yielded a total of three species of Mysidae, altogether previously poorly known or unknown to science. Pseudomma kryotroglodytum sp. nov. is described, based on the structure of the antennal scale, telson and on cornea-like lateral portions set off against the main body of eyeplates. Mysidetes illigi is re-established at species level after almost a century in synonymy. Re-descriptions are provided for M. illigi and M. hanseni, based on types and ice cave materials. Keys to the Southern Ocean species of Pseudomma and to the world-wide species of Mysidetes are given. Phylogenetic trees are provided for the genera Pseudomma and Mysidetes. 18S rDNA sequences of P. kryotroglodytum differ from GenBank sequences of other Pseudomma species. First sequence data are given for species of the genus Mysidetes: 18S differs between the two examined species and COI is quite diverse between and within species. We found previously unknown, probably sensorial structures in these ice cave species: in P. kryotroglodytum, the basal segment of the antennula shows a pit-like depression with striated pad on the bottom and a median cyst, connected with the bottom of the eyeplate cleft. M. illigi shows a female homologue of the appendix masculina bearing a field of modified setae. Subsequent investigations demonstrated these structures also in species from other habitats. The feeding apparatus and stomach contents of the three ice cave species point to brushing of small particles (detritus, microalgae) from available surfaces, such as sediment, rock and the ice surface. Differences in the feeding apparatus are very subtle between the two Mysidetes species. The high content of fat bodies in M. hanseni could help it to survive periods of starvation. The large storage volume of the foregut in P. kryotroglodytum points to the collection of food with low nutritional quality and could help to balance strongly fluctuating food availability. Summer specimens of M. hanseni showed a bimodal frequency of developmental stages in the marsupium and bimodal size-frequency distribution of free-living stages. The females with younger brood (embryos) were, on average, larger and carried more marsupial young than those with older brood (nauplioid larvae). All examined incubating and spent females showed (almost) empty foreguts and empty ovarian tubes, suggesting possible semelparity and death following the release of young. The absence of juveniles and immature females from summer samples suggests that growth and accumulation of fat and yolk occur outside ice caves, while such caves could be used by fattened adults as shelter for brooding. A provisional interpretation proposes a biannual life cycle for M. hanseni, superimposed with shifted breeding schedules, the latter characterised by early breeding and late breeding females, probably in response to harsh physical and trophic conditions along the continental coast of Antarctica.

We have determined the mineral composition of statoliths in 169 species or subspecies (256 populations) of the family Mysidae on a worldwide scale. Including previously published data, the crystallographic characteristics are now known for 296 extant species or subspecies: fluorite (CaF2) in 79%, vaterite (a metastable form of crystalline CaCO3) in 16%, and non-crystalline (organic) components in 5%, the latter exclusively and throughout in the subfamilies Boreomysinae and Rhopalophthalminae. Within the subfamily Mysinae vaterite or fluorite were found in three tribes, whereas other three tribes have fluorite only. The exclusive presence of fluorite was confirmed for the remaining seven subfamilies. Hotspots of vaterite were found in Amazonia and the Pontocaspis, in each case with reduced frequencies in main and tributary basins of the Atlantic and N-Indian Ocean. Vaterite is completely absent in the remaining aquatic regions of the world. In accordance with previous findings, fluorite occurred mainly in seawater, vaterite mostly in brackish to freshwater. Only vaterite was found in electrolyte-poor Black Water of Amazonia, which clearly cannot support the high fluorine demand for renewal of otherwise large fluorite statoliths upon each moult. Vaterite prevails in Diamysini, distributed over most of the area once occupied by the Tethyan Sea. It also prevails in Paramysini with main occurrence in the Pontocaspis, where fossil calcareous statoliths in the stable form of calcite are known from Miocene sediments of the brackish Paratethys. Four Recent genera from three tribes are heterogeneous in that they comprise both vaterite- and fluorite-precipitating species. Previous hypotheses are expanded to cover greater geographic and time scales, proposing that fluorite-bearing marine ancestors penetrated freshwaters in Tethyan and Paratethyan basins, where they developed precipitation of vaterite. This gave their successors predispositions for shifting into separate evolutionary lines from fluorite to vaterite precipitation and vice versa .