ULTRASTRUCTURE AND RAPID AXOPODIAL CONTRACTION OF A HELIOZOA, RAPHIDIOPHRYS CONTRACTILIS SP-NOV

In the present study, we isolated a species of heliozoans from a brack ish pond in Shukkeien Garden, Naka-ku, Hiroshima City, Japan. Electron -microscopic observations showed that the axonemal microtubules in thi s heliozoan constituted a complex pattern of hexagons and triangles. B y applying SDS-polyacrylamide gel electrophoresis and subsequent immun oblotting, molecular weights of alpha- and beta-tubulins were determin ed to be 48 and 45 kDa, respectively. X-ray microanalysis demonstrated that the numerous scales coating the cell body surface were silicic s tructures. Size and shape of the cell body and the scales were examine d and compared with other known species of heliozoans, which led us to conclude that this is a new species belonging to the genus Raphidioph rys. This heliozoan was also found to carry out rapid axopodial contra ction during food uptake at a velocity of about 1 mm/s. With reference to this characteristic contractile behavior, this new species was nam ed Raphidiophrys contractilis.