The Fine Structure of Fuscheria terricolaBerger et al., 1983 and a Proposed New Classification of the Subclass Haptoria Corliss, 1974 (Ciliophora, Litostomatea)

Abstract

Summary The general fine structure of Fuscheria terricola Berger, Foissner and Adam , 1983 is very similar to that of other haptorid ciliates. However, a tela corticalis and parasomal sacs are absent. Fuscheria terricola has doughnutshaped mucocysts and unique nail-shaped toxicysts. Their nail-like appearance is due to a conspicuous posterior thickening of a fibro-granular material surrounding the rod-shaped center which is very similar to the pexicysts of Acropisthium and Didinium. The somatic kinetids are monokinetids with the classical haptorian fibrillar associates. In addition, the upper 4 to 7 somatic kinetids in each kinety possess nematodesmal bundles. At the base of the oral cone there is a circumoral kinety composed of typical haptorian dikinetids. Their nematodesmal bundles and those from the upper somatic kinetids form a highly characteristic irregular rhabdos. Acropisthium and Actinorhabdos show the same oral organization as Fuscheria. Hence, these 3 genera are united in the new family Acropisthiidae nov. fam. The rhabdos of most members of the subclass Haptoria is built up of 3 microtubular components: a) the transverse microtubular ribbons which originate from the nonciliated kinetosomes of oral dikinetids or from ciliated or nonciliated oralized somatic kinetids and turn to the center of the oral bulge, where they plunge inwards to support the cytopharynx; b) the nematodesmal bundles which form an “outer rhabdos”; and c) the vertically oriented bulge microtubules which are distributed rather regularly in the marginal area of the oral bulge and grouped in nematodesmata-like bundles in the lower oral region, where they form a more or less pronounced “inner rhabdos”. Exceptions from this pattern are the Cyclotrichina which lack nematodesmata and the Archistomatida which lack bulge microtubules, probably because of the absence of toxicysts. The term “oralized somatic kinetids” is suggested for such kinetids which lie within somatic kineties, but bear nematodesmal bundles contributing to the rhabdos. Such kinetids may be monokinetids or dikinetids; they may or may not be associated with normal haptorid oral dikinetids; and they may be ciliated or nonciliated. The different kinds of kinetids which contribute to the rhabdos and the dorsal brush (presence/absence) are the clue characters for a revised classification of the Haptoria. The following new higher taxa are erected: Enchelyina nov. subord. (with nonciliated oralized somatic monokinetids), Acropisthiina nov. subord. (with oral dikinetids and ciliated oralized somatic monokinetids), Spathidiida nov. ord. (with oral dikinetids only), Litonotina nov. subord. (right oral kinety associated with somatic monokinetids), Pseudoholophryida nov. ord. and Pseudoholophryina nov. subord. (dorsal brush absent or highly aberrant), Helicoprorodontina nov. subord. (oralized somatic dikinetids, dorsal brush probably absent).