2019 Volume 70 Issue 1-2 Pages 101-108
In late August 2014, a living polycystine radiolarian assemblage was collected from the surface waters off the shore of Sakata, Yamagata Prefecture, in the eastern margin of the Japan Sea. The assemblage was dominated by the spumellarian Spongosphaera streptacantha, and included a few individuals of Pseudocubus obeliscus and Tetrapyle octacantha. The intraspecific variation in S. streptacantha observed in the main spine and spongiose layer was thought to reflect skeletal growth. Morphometric analysis of the main spine and spongiose layer indicated that most individuals of S. streptacantha were growing. On the sampling day, the surface water attained the annual maximum water temperature and was strongly influenced by the Tsushima Warm Current. S. streptacantha inhabited the summer surface water of this ocean area almost exclusively.
