Phylogenetic position of Karotomorpha and paraphyly of Proteromonadidae.

The taxon Slopalinida (Patterson, 1985) comprises two families of anaerobic protists living as commensals in the intestine of vertebrates. The proteromonadids are small Xagellates (ca. 15 m) with one nucleus, a single large mitochondrion with tubular cristae, Golgi apparatus and a Wbrillar rhizoplast connecting the basal bodies and nucleus (Brugerolle and Mignot, 1989). The number of Xagella diVers between the two genera belonging to the family: Proteromonas, the commensal of urodelans, lizards, and rodents, has two Xagella, whereas Karotomorpha, the commensal of frogs and other amphibians, has four Xagella. The surface of the cell is folded, the folds are supported by single microtubules (Proteromonas) or by ribbons of several laterally interconnected microtubules (Karotomorpha). The transitional Xagellar region contains double transitional helix. The posterior part of Proteromonas cell is covered with Wne tubular hairs— the somatonemes (Brugerolle and Joyon, 1975). The representatives of the second family—Opalinidae— are quite diVerent from the proteromonadid Xagellates. They are multinucleated and multiciliated, often large (up to several mm). They are common commensals of frogs, some can inhabit the intestine of urodelans or Wsh. The family comprises three binucleated genera (Protoopalina, Protozelleriella, Zelleriella) and two genera with up to hundreds of nuclei (Cepedea, Opalina). Besides nuclei the cell contains a large number of mitochondria with tubular cristae, Golgi complexes and small digestive vacuoles (Delvinquier and Patterson, 1993). The cell surface is heavily folded, the folds are supported by ribbons of microtubules in a very similar way as in Karotomorpha. The ultrastructure of Xagellar transi-