Regular axopodial activity of Diplosphaera hexagonalis Haeckel (spheroidal spumellarian, Radiolaria).

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Abstract

The physiological ecology of a spherical polycystine species, Diplosphaera hexagonalis collected from the surface water of the Kuroshio Current in the East China Sea off Sesoko Island, Okinawa, was observed in a culture dish for three days. The observed specimen demonstrated cyclic extension and contraction of axopodia by a regular interval of ca. 630 seconds. Each cycle was divided intro four phases based on the state of the axopodia and movement of axopodial vacuoles. Vertical migration in response to axopodial motility was also observed. The specimen began to rise accompanied with the axopodial extension, floated in the seawater and often moved horizontally when its axopodia were radiated symmetrically, and began to sink in correspondence with the axopodial contraction. The effect of thermal currents on this behavior is easily neglected on the ground of the definite coincidence with the rhythmic extension and contraction of axopodia. The rhythm appears to play important roles in the physiological ecology of this species, including food capture and possibly buoyancy. The taxonomic section presents a nearly complete synonym list of D. hexagonalis and summarizes that the genus Diplosphaera is a senior synonym of Astrosphaera, Drymosphaera and Leptosphaera. Thus, Diplosphaera hexagonalis is the only valid name for this species, according to ICZN Article 55.3. Diplosphaera is considered herein to belong not to the family Actinommidae but to the Astrosphaeridae, unlike in most previous paleontological and biological studies. The family Macrosphaeridae Hollande and Enjumet, 1960, to which the genus Diplosphaera was assigned, is treated as an invalid name because the type genus Macrosphaera has not been established yet.

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