Nahecaris stuertzi, a phyllocarid crustacean from the Lower Devonian Hunsrück Slate

Abstract

Restudy ofNahecaris based on new stereo radiographs and re-examination of actual specimens has added the following new information.Nahecaris ranges in shape from long and slender to short and stout, the carapace from deep and rounded to long and narrow. Carapace ornament consists either of thin ridges parallel to the ventral border or inclined rows of irregular lines or cusps, but these characters cannot be consistently correlated with other variables to permit definition of separate species. The carapace is fused to the head, and possibly to the anterior end to the thorax in the area in front of the median dorsal plate. A post-mandibular pyritised band may represent the carapace adductor muscle, which inserts on the mesolateral carinae. The mandible resembles that ofCeratiocaris, while the maxillae are like those of extant leptostracans. The 8 thoracopods are biramous: they have an exopod with finger-like lobes and a stenopodous endopod. Posteriorly the endopods reduce markedly, forming a conical, anteriorly open feeding basket. The predominance of dorso-ventrally flattened specimens, and the wide ventral gape of the carapace valves suggests those valves were spread apart in life.Nahecaris may have pressed itself to the substrate by flexing the carapace rim outward and incurving the ventral region of the carapace. The stout second antennae may have stabilised and propelled the animal over the substrate.Nahecaris is thought to have been benthic and to have fed, likeCeratiocaris, by lifting the substrate into suspension, as well as by picking up large fragments directly with the mandibles.