Light and transmission electron microscopy of Cepedea longa (Opalinidae) from Fejervarya limnocharis.

Cepedea longa Bezzenberger, 1904, collected from Fejervarya limnocharis (Amphibia, Anura, Ranidae) from Honghu Lake, Hubei Province, China in May-July 2016, is described at both light and transmission electron microscope levels. This is the first electron microscopic study of this species. Cepedea longa possesses a developed fibrillar skeletal system, composed of longitudinal fibrillar bands and transversal fibrils as well as numerous thin microfibrils dispersed in the endoplasm, which may play an important role in morphogenesis and offer some resilience to deformations of the cell. Longitudinal microfibrils are polarizing elements of kineties, bordering the somatic kineties on the left side and possibly responsible for kinetosome alignment. Two types of vesicles exist in the somatic cortex: globular endocytotic vesicles and flattened exocytotic vesicles. As to the nuclei of C. longa, a thick microfibrillar layer was observed to attach to the cytoplasmic face of the nuclear envelope. This fact suggests no necessary connection between the presence of this microfibrillar layer and the number of nuclei. In addition, some unknown tightly-packed microtubular structures in the nucleoplasm were observed for the first time in opalinids; neither their nature nor physiological significance is known. A detailed list of all reported Cepedea species is included.