Fine Structure of the Nuclei of the Karyorelictean Ciliate Tracheloraphis flexuosus from the Japan Sea

Abstract

The nuclear apparatus of the Japan sea population of Tracheloraphis flexuosus RAIKOV et KOVALEVA 1968 consists of a longitudinal row of 20–30 macronuclei and 10–15 micronuclei usually arranged into groups of two macronuclei and one micronucleus in each. The nuclear groups lie in a voluminous perinuclear lacuna, the proximal membrane of which tightly applies to the nuclei leaving around them only a thin rim of ground cytoplasm. This membrane encircles each nuclear group separately and apparently holds the nuclei together. The micronuclei are filled with spongy condensed chromatin and limited by a conventional envelope with pores. The micronuclear chromatin is resistant to bleaching with BERNHARD's EDTA. Young macronuclei occur in some groups and contain small scattered chromocentres but no nucleoli; the chromocentres are readily bleached with EDT A. Adult macronuclei contain several nucleoli of usual structure (fibrillar core, granular cortex), several chromocentres and rarely a small sphere. The chromocentres are heterogenous: each one shows a dense cap. They become bleached with EDTA even after short exposure whereas nucleoli and the sphere retain contrast. The nuclei of Tracheloraphis flexuosus are smaller than those of T. dogieli, the similar European form.