Morphology, palaeobiology and phylogeny of Oryctocaris balssi gen. nov. (Arthropoda), a phyllocarid from the Lower Devonian Hunsrück Slate (Germany)
Nahecaris balssi Broili, 1930 is a phyllocarid crustacean known only from the Lower Devonian Hunsrück Slate in Germany. This study redescribes the species on the basis of 22 new specimens and the holotype. Phylogenetic analysis of several Palaeozoic phyllocarids reveals that N. balssi and N. stuertzi Jaeckel, 1921 are not congeneric, as was previously assumed, and that there are significant morphological differences between these taxa. Thus, the new genus Oryctocaris is erected for N. balssi, characterized mainly by the absence of a rostrum and a median dorsal plate. It is suggested that O. balssi was a fairly active swimmer, which was not limited to the benthic zone. Furthermore, the species presumably swam by means of powerful pleopod strokes coupled with downward movements of the abdomen. It is likely the telson spine with its furcal rami acted as a paddle, enhancing propulsion. We suggest that O. balssi was a deposit feeder, foraging by digging in the mud and picking up food particles or small hard-shelled organisms such as molluscs, which were then crushed by the large and robust mandibles.