Die morphogenese von Urosoma macrostyla ( Wrześniowski, 1870) (Ciliophora: Oxytrichidae))

Abstract

Summary The morphogenesis of the hypotrichous ciliate Urosoma macrostyla ( Wrześniowski , 1870) was investigated. 12 stages of the cortical and nuclear fission are described and depicted. The overall pattern of the morphogenetic events is similar to that known from other Oxytrichidae. However, there are 2 details which enable us to elucidate the systematic position of this genus within the Oxytrichidae. The morphogenesis starts with a proliferation of the basal bodies for the oral primordium close by the 3 postoral ventral cirri. 5 primary primordia which are situated predominately at the frontal area of the parental animal evolve from the oral primordium, the postoral ventral cirri, and the lowest of the posterior frontal cirri. The primary primordia break up during the middle stages of the morphogenesis and form secondary primordia: the anterior ones become the anlagen of the frontoventral cirri of the proter, the posterior ones become the anlagen of the frontoventral cirri of the opisthe. Anlage 1 evolves from the oral primordium in the opisthe, but in the proter it develops from the buccal cirrus. The anlagen 1 to 6 generate 1, 2, 3, 3 (4), 4, 5 (4) frontoventral cirri. The development of the dorsal kineties proceeds according to typ 2 and shows no special features. The peculiar mode of the origin of the anlagen of the frontoventral cirri and of the anlage 1 of the proter shows that the closest related genus is Gonostomum whose morphogenetic pattern coincide in this respect with that one of Urosoma. Some other features, e.g. the structure of the oral apparatus and the fact that 6 frontal cirri are not transformed into anlagen during the morphogenesis, support the view that these 2 genera are very closely related. However, in spite of these similarities, both genera are valid, because they differ in the mode of the origin of the dorsal kineties, the development of the cirri within the anlagen, the body form, the postoral ventral cirri, and the pattern of the frontal cirri.