Divisional Morphogenesis in Amphisiellides illuvialis N. Sp., Paramphisiella caudata (Hemberger) and Hemiamphisiella terricola Foissner, and Redefinition of the Amphisiellidae (Ciliophora, Hypotrichida)

Classification of hypotrich ciliates is bewildering, possibly due to many unrecognized convergencies and the lack of detailed ontogenetic data in most species. A puzzling case are hypotrichs which have an obliquely extending “median cirral row” on the ventral surface between the right and left marginal cirral row. Such species are often assigned to the poorly defined family Amphisiellidae. However, we show by a comparative analysis of the divisional morphogenesis of three amphisiellid morphotypes and by a reevaluation of literature data that a median cirral row can be formed by at least four non‐homologous processes. These data are used to define the “amphisiellid median cirral row/’(a row containing all or most cirri from at least two rightmost anlagen, arranged one behind the other during cytokinesis), to redefine the Amphisiellidae (Euhypotrichina with an amphisiellid median cirral row of which the anterior segment is formed by cirri of the rightmost ventral anlage and the posterior segment by cirri of the second ventral anlage from right; a middle segment may be formed by neighboring anlagen), and to improve the diagnoses of the seven genera assigned by us to this family. Attempts to reconstruct the evolution within the Amphisiellidae failed, in spite of the detailed morphological and ontogenetic data available. We thus conclude that such data, although highly valuable, are insufficient to light up the supergeneric phylogeny of hypotrich ciliates. For this, molecular markers and investigations of the morphogenetic processes at electron microscopic level appear indispensable.