Nephrospyris knutheierisp.n., an extant trissocyclid radiolarian (Polycystinea: Nassellarida) from the Norwegian-Greenland Sea

Abstract
Skeletons produced by the trissocyclid Polycystinea are rare or absent in surface sediments of the boreal Atlantic and the Norwegian-Greenland Sea, and the few species that have been observed are cosmopolitan in distribution. Examination of Polycystine a in 268 sediment core tops and six plankton tows from the Norwegian-Greenland Sea indicates that a new species, Nephrospyris knutheieri, is restricted to the Icelandic Current. This species may also occupy the East Greenland Current north of Jan Mayen, where the underlying sediments are largely unfossiliferous. High salinities (≥ 35%) of the warm waters flowing north through the Shetland-Faroe Channel and the Denmark Strait may impede the eastward and southward penetration of N. knutheieri into the Norwegian Basin and Labrador Sea, respectively. The species is easily distinguishable from warm-water and Antarctic trissocyclids. There is a homeomorph in the Subarctic Province of the North Pacific, Nephrospyris ?pervia, which appears to have similar water-mass tolerances (temperature 2-6°C; salinity 33-34.5% ). N. knutheieri shares some of the skeletal characteristics of the two modern morphs of N. ?pervia but differs from them in other properties. On the basis of the present data, it cannot be determined whether N. knutheieri and N. ?pervia are conspecific, or whether they represent independent genetic units. The frigid character of the modern Arctic Ocean is probably an effective barrier to the continuity of this complex of morphs. The evolution of N. ?pervia is well documented in the Neogene sediment record of the North Pacific. No immediate precursor to N. knutheieri has been found in subsurface sediments of the Norwegian-Greenland Sea recovered on Deep Sea Drilling Project Leg 38. It is concluded that N. knutheieri has N. ?pervia as its precursor and was introduced into the Norwegian-Greenland Sea from the North Pacific within the past 900 000 years. The genus Nephrospyris is emended.