Endemism and speciation in the polycystine radiolarian genus Actinomma in the Arctic Ocean: Description of two new species Actinomma georgii n. sp. and A. turidae n. sp.

Evidence, based on the species and high rank taxa composition and level of domination, skeletal morphological diversity and distributional data of radiolaria from sediment samples, is presented in support of a hypothesis of endemism for the Arctic polycystine fauna, especially arctic actinommids, as presented in the Discussion section. The arctic assemblages have low diversity, few species and very high level of domination of Actinommidae and Cannobotryidae. Two new endemic species, Actinomma georgii and A. turidae, are described based on their unique skeletal morphology. Although the geographic origins of these novel actinommids cannot be determined precisely based on existing knowledge of radiolarian reproductive processes and population biology, the preponderance of evidence presented here suggests that the unique features of the Arctic Ocean environment may contribute to elevated local speciation, and that the remarkable variability in skeletal morphology of Arctic Ocean actinommids may be enhanced by strong environmental selection pressures favoring relatively rapid speciation of polycystines in this high latitude oceanic regime. These actinommid species, including Actinomma boreale, without a 4th shell, are considered to be endemic and reproducing within the Arctic Ocean, suggesting that the two new species are environmentally adapted only to the particular environment of the Arctic Ocean. By contrast, A. boreale without a 4th shell is likely less adapted to this oceanic regime.