Hexabathynella halophila gen. n., sp. n. und die Frage nach der marinen Abkunft der Bathynellacea (Crustacea: Malacostraca)

All species of Bathynellacea, known to occur in the immediate vicinity of the sea, belong to the same genus, Hexabathynella gen. n. The species are: H. pauliani, H. knoepffleri, H. tenera. Also included into the new genus are the fresh-water species H. hebrica, H. szidati, H. minuta. To these, a new species, H. halophila sp. n., is added; it was found at a salinity of 27‰ and is the first representative of the Bathynellacea recorded from polyhaline waters. A simple experiment revealed that the new species is likely to be extremely euryhaline. Current opinion as to the marine origin of the Bathynellacea is criticized in the light of new evidence resulting from recent studies on the evolution and systematic relationships within this order. Contrary to common belief, the Bathynellacea did not colonize the fresh-water mesopsammal via the mesopsammal of marine sandy beaches. The extant Bathynellacea most likely derived from ancestors which lived in fresh-water lakes or running surface waters. They became distributed in their mesopsammal habitat. The occurrence of some species of Hexabathynella gen. n. in oligohalime to polyhaline waters is secondary.