Morphology and Morphogenesis of Onychodromus quadricornutus n. sp. (Ciliophora, Hypotrichida), an Extraordinarily Large Ciliate with Dorsal Horns1

Abstract

The morphology and the morphogenesis of the freshwater hypotrich ciliate Onychodromus quadricornutus n. sp. have been investigated using living organisms, protargol impregnation, and scanning electron microscopy. Some preliminary and supplementary results about the morphogenesis of O. grandis and Laurentiella acuminata are included. The new species is unique among all described hypotrichs in having four dorsal horns, whose function is unknown. In addition, O. quadricornutus is probably the most voluminous hypotrich ciliate known (2 times 10‐6‐5 times 106μm3). Its morphogenetic pattern resembles the oxytrichids O. grandis and L. acuminata. The strongest apomorphic character, which unites these three species, is probably the multiple fragmentation of the dorsal primordia during morphogenesis. This fragmentation causes the characteristic high number and more or less irregular distribution of the dorsal kineties in the non‐dividing individuals.

Evolution of Morphogenetic Processes in the Orthoamphisiellidae N. Fam., Oxytrichidae, and Parakahliellidae N. Fam., and Their Depiction Using a Computer Method (Ciliophora, Hypotrichida)

“…25. Onychodrontus quadricornutus Foissner, Schlegel & Prescott, 1987 [37]. The only parakahliellid species in which obviously both anlagen-parts of N1 develop in the third ventral row from right (row 11).…”

A Redescription of the Morphology of Onychodromus grandis Stein 1859 and the Systematic Implications of its Morphogenesis

“…It seems that the presence and number of these horns is one of the most important characters in the course of the identification of the species of genus Onychodromus. These are special traits of the dorsal side, and not homologous with the caudal appendices of Aspidisca and Psiiotricha species [6]. The function of these horns has not yet been completely understood.…”

“…The number of ventral cirri in our population always exceeds 5 (Min = 9; Max = 9; x = 9; SO = 0,O; Sx = 0,O) which, together with the number of frontal ones (Min = 12; Max = 13; x = 12, 2; SO = 0, 42; Sx = 0, 13) clearly separates it from Stylonychia grandis (Hemberger, 1982). According to our observations, individuals of the populations studied had 13 cim (FC:3 + 0. quadricornutus has four horns [6], while 0. indica Kamra and Sapra [13] has about 3 horns and a smaller swelling. It seems that the presence and number of these horns is one of the most important characters in the course of the identification of the species of genus Onychodromus.…”

“…simplex by Szabo ( Morphogenesis of the species was only approximately known from Stein's description [17]. The development of oral primordia is apokinetal and not related to the transversal cim [6]. In 0. quadricornutus [6] and 0. indica [ 131 the oral primordium develops close to TC, and TC, while in 0. grandis it develops in the vicinity of TC,.…”

“…Marginal cim developed in this way shift slightly to the right then, as in most Oxytrichids. According to Kamra and Sapra [ 131 only the first dorsal primordium from the left fragments, while Foissner et al [6] mention several fragmentations of primordia. On the basis of our observations, dorsal primordia of 0. grandis except for the middle row divide only twice or three times, whereas in 0. quadricornutus and 0. indica rows of dorsal primordia fragment many times [6,131.…”