FINE-STRUCTURE OF COSMOCOLPODA-NASCHBERGERI (CILIOPHORA, COLPODIDA)

In both the light and scanning electron microscope, Cosmocolpoda naschbergeri FOISSNER, 1993 looks rather dissimilar to other members of the order Colpodida due to its unique cortical ornamentation, viz. 1-2 mum high, equidistantly spaced crests which extend between the somatic ciliary rows. A transmission electron microscope study was thus put forward to substantiate the colpodid affinity suggested by some light microscopic observations and to establish whether the peculiar ornamentation is associated. with special ultrastructural characteristics. The cortical ultrastructure and the fibrillar associates of the somatic dikinetids of C. naschbergeri are very similar to those described from members of the order Colpodida, especially to those known from small Colpoda species, viz. C. steinii and C. maupasi. However, extrusomes (mucocysts, trichocysts) are absent and the epiplasmic layer, which is continuous with the cortical crests, is thicker than in other small colpodids and might help to stabilize the cortical ornamentation. No other special differentiations were found in the crests which contain mitochondria and a tubular cistern of the granular endoplasmic reticulum. It is concluded that C. naschbergeri ist closely related to the genus Colpoda. The ornamentation of its cortex is apparently a young evolutionary acquisition.