Ultrastructure and Ecology of Calycomonas ovalis Wulff, 1919, (Chrysophyceae) and Its Redescription as a Testate Rhizopod, Paulinella ovalis N. Comb. (Filosea: Euglyphina)


  • This research was supported, in part, by the Biological Oceanography Program of the National Science Foundation through grants OCE-8511365 and OCE-8710085 and by the National Sea Grant Program through grant MPD-8706. We acknowledge Gregg Tracey who first drew our attention to the Aureococcus bloom, Linda Hufnagel for use of the JEOL 1200 STEM, David Browning for conducting the X-ray spectroscopy, Richard Chaisson of Olympus Corporation for loan of the negative phase contrast objective, Ken Johnson for translating German references, Dag Klaveness for additional references, and two anonymous reviewers.


An exceptional bloom (109 cells/liter) of a unicellular alga, Aureococcus anophagefferens, in Narragansett Bay, RI, was accompanied by unusually high numbers (6 times 106 tests/liter) of vase-shaped cells of Calycomonas ovalis Wulff, hitherto considered a flagellated chrysophyte. Phase contrast light microscopy showed the characteristic oval lorica or test of C. ovalis, ca. 3.0 times 4.5 μm. Transmission electron microscopy of thin sections of natural populations revealed, however, that C. ovalis is actually a rhizopod within a test of electron-dense scales. This estuarine, planktonk testacean extends a pseudopodium through a narrow pseudostome and lacks chloroplasts or flagella. It is a bacterivore and feeds primarily on unicellular cyanobacteria. The morphology, ultrastructure, and cell division of C. ovalis are described. These characteristics place C. ovalis with the genus Paulinella (Sarcodina: Filosea: Euglyphina), which at present contains the single species, P. chromatophora Lauterbom. Calycomonas ovalis is thus assigned to Paulinella as P. ovalis n. comb.