Two new living Entactinaria (Radiolaria) species from the Arctic province: Joergensenium arcticum n. sp. and Joergensenium clevei n. sp.

• Two new living Entactinaria species in the Arctic Ocean are described.
• Taxonomic position of the order Entactinaria is discussed and the genus Joergensenium has been emended.
• New species reflect distinct local environmental conditions in the Arctic Ocean.
• Three-dimensional imaging using MXCT is a reliable tool for studying radiolarian skeletal structure.

Radiolarians in the Arctic Ocean have been studied lately in both plankton and sediment trap samples in the Chukchi Sea area. These studies have shed light on new radiolarian taxa, especially within the order Entactinaria, including two new species of Joergensenium, Joergensenium arcticum from the western Arctic Ocean, so far restricted to the Pacific Winter Water in the Chukchi Sea, and Joergensenium clevei hitherto found in the northern part of the Norwegian Sea south of the Fram Strait. The taxonomic position of the order Entactinaria is discussed and the genus Joergensenium has been emended. We have also observed in detail the internal structure of Joergensenium arcticum using Microfocus X-ray Computed Tomography and have utilized three-dimensional imaging for the first time in a species description.