Ultrastructure and Rapid Axopodial Contraction of a Heliozoa, Raphidiophrys contractilis Sp. Nov.

ABSTRACT. In the present study, we isolated a species of heliozoans from a brackish pond in Shukkeien Garden, Naka-ku, Hiroshima City, Japan. Electron-microscopic observations showed that the axonemal microtubules in this heliozoan constituted a complex pattern of hexagons and triangles. By applying SDS-polyacrylamide gel electrophoresis and subsequent immunoblotting, molecular weights of α and β-tubulins were determined to be 48 and 45 kDa, respectively. X-ray microanalysis demonstrated that the numerous scales coating the cell body surface were silicic structures. Size and shape of the cell body and the scales were examined and compared with other known species of heliozoans, which led us to conclude that this is a new species belonging to the genus Raphidiophrys . This heliozoan was also found to carry out rapid axopodial contraction during food uptake at a velocity of about 1 mm/s. With reference to this characteristic contractile behavior, this new species was named Raphidiophrys contractilis .