Comparison of divisional morphogenesis in four morphologically different clones of the genus Gonostomum and update of the natural hypotrich system (Ciliophora, Hypotrichida)

Abstract

Summary Divisional morphogenesis of a clone of the multimacronucleate Gonostomum kuehnelti Foissner, 1987 (clone I), with four transverse cirri and of three clones of Gonostomum affine (Stein, 1859) Sterki, 1878, with two macronuclear segments are described and compared using protargol impregnation. The three clones of G. affine differ in having two (clone II), four (clone III) and six (clone IV) transverse cirri, whereas all clones completely lack ventral cirri between proximal membranelles and transverse cirri. Early morphogenetic processes show that all four clones develop the family characters of the Oxytrichidae Ehrenberg, 1838: “neokinetal 3” anlagen and long primary primordia. Only clone I shows a significant morphogenetic difference by generating proter's first (left) frontal cirrus by the oral primordium. Clones II to IV generate this cirrus de novo. Biometry of middle dividers and specimens in interphase reveals an invariable cirral pattern generated from six ventral anlagen in clone I, whereas six or seven ventral anlagen, one or two left marginal rows and two to four macronuclear segments develop in clones II–IV. All four clones are, however, stable in the lack of ventral cirri and, surprisingly, clones II–IV are also stable (not overlapping) in their different number of transverse cirri. Nevertheless, morphologic differences in clones II–IV are considered to be probably polymorphic states of G. affine . Recently published morphogenetic data are analyzed, shown in schematized computer drawings and added to the natural hypotrich system: Lamtostyla edaphoni is transferred to the genus Amphisiella Gourret and Roeser, 1888 within the family Oxytrichidae because of neokinetal 3 anlagen and long primary primordia development. Onychodromopsis flexilis is also assigned to the Oxytrichidae because of neokinetal 3 and long primary primordia, whereas Sterkiella histriomuscorum generates “neokinetal 1” anlagen and long primary primordia are absent and therefore it is assigned to the family Parakahliellidae. A computer generated tree is presented using the programs MacClade and PAUP and consisting of 42 morphogenetically investigated hypotrich species with 6 characters in 15 states. For the homonym Clara the genus name Tetmemena nom. nov. is suggested.