Light and Electron Microscopical Observations on the Stomatogenesis of the Ciliate Coleps amphacanthus Ehrenberg, 1833

ABSTRACT Light and electron microscopical observations on the stomatogenesis of Coleps amphacanthus Ehrenberg, 1833, show that this “gymno”‐stome ciliate has a well developed oral ciliature made of 19–23 “paroral dikinetids” and three “adoral organelles.” These structures were previously known as “circumoral ciliature” and “dorsal brosse,” and it was thought that they originated from the distal ends of all the 22–26 somatic kineties. Contrary to this view, only four stomatogenic kineties (K1, Kn, Kn‐1, and Kn‐2) are involved in stomatogenesis of the opisthe. All paroral dikinetids arise from one single kinetofragment (KF1) to the right of the oral anlage while the adoral organelles originate from the three left kinetofragments (KFn, KFn‐1, and KFn‐2). In particular, the future paroral dikinetids perform a complex morphogenetic movement that leads to a situation where the postciliary microtubules of the once posterior kinetosome of each oral dikinetid give rise to the cytopharyngeal microtubular ribbons. The postciliary origin of the cytopharyngeal ribbons which could only be detected by an EM study of stomatogenesis shows that the basket of Coleps belongs to the cyrtos‐type and not to the rhabdos‐type basket, where transverse microtubules accompany the basket‐forming nematodesmata. The taxonomic implications of these observations, which may lead to a revision of the systematic position of the genus Coleps , are discussed.