Data from: Zoogeography of epigean freshwater Amphipoda (Crustacea) in Romania: fragmented distributions and wide altitudinal variability

Inland epigean freshwater amphipods of Romania are diverse and abundant
for this region has a favourable geographical position between the Balkans
and the Black Sea. Excluding Ponto-Caspian species originating in brackish
waters and freshwater subterranean taxa, there are 11 formally recognized
epigean freshwater species recorded from this country. They belong to 3
genera, each representing a different family: Gammarus (Gammaridae, 8
species or species complexes), Niphargus (Niphargidae, 2 epigean species)
and Synurella (Crangonyctidae, one species). Their large-scale
distribution patterns nevertheless remain obscure due to insufficient
data, consequently limiting biogeographical interpretations. We provide
extensive new data with high resolution distribution maps, thus improving
the knowledge of the ranges of these taxa. Gammarus species display
substantial altitudinal variability and patchy, fragmented distribution
patterns. They occur abundantly, particularly in springs and streams, from
lowlands to sub-mountainous and mountainous regions. In the light of
recent molecular research, we hypothesize that the complex
geomorphological dynamics of the Carpathian region during the Late
Tertiary probably contributed to their allopatric distribution pattern.
Contrasting with Gammarus, the genera Niphargus and Synurella exhibit low
altitudinal variability, broad ecological valences and overlapping
distributions, being widespread throughout the lowlands. The current
distribution of N. hrabei and N. valachicus seems to be linked to the
extent of the Paratethys during the Early Pliocene or Pleistocene. We
further discuss the taxonomic validity of two synonymized and one
apparently undescribed taxon, and provide an updated pictorial
identification key that includes all taxa and forms discussed in our
study. The mosaic distribution of epigean freshwater amphipod species in
Romania shows that this region is particularly suitable for phylo- and
biogeographical analyses of this group.