New Combination of the "Rhizarian Rider" Phenomenon, Brachyscelus crusculum Bate, 1861 (Crustacea, Amphipoda, Brachyscelidae) and Odontosphaera sp. (Radiolaria, Collodaria, Collosphaeridae).

A new combination of the "rhizarian rider" phenomenon was observed in the sea area affected by the Kuroshio current, off Japan: a female of Brachyscelus crusculum (Crustacea, Amphipoda, Brachyscelidae) holding a colony of Odontosphaera sp. (Radiolaria, Collodaria, Collosphaeridae). The "rhizarian rider" phenomenon of Collosphaeridae and B. crusculum was first recorded. The large colony size (ca. 13 mm) and color (pale blue) of Odontosphaera sp. are also newly reported by this study. Brachyscelus crusculum presumably utilizes Odontosphaera sp. as a float, food source, and breeding bed.