Choice of out-groups
The major question whether to choose one or several taxa that could be used as out-groups for this analysis was related to polymorphisms among the species included in the family Kirchenpaueriidae, and to the lack of a general recent revision for this family. Bouillon’s (1985) synopsis, which recognized five genera in the family, constitutes a unique compendium for classification of the group.
The genus Halicornopsis Bale, 1882, includes two known species, both distributed in Australian waters. Halicornopsis elegans Lamarck, 1816 and H. avicularis Bale, 1882 are poorly known species that have been recorded only a few times. Halicornopsis is characterized by the denticulated rim of the hydrothecal aperture (Bouillon, 1985), a feature also shared with some genera of the family Aglaopheniidae. Because of this we decided not to consider this genus within the potential out-groups for Oswaldella due to its uncertain position.
The genus Ophinella Stechow, 1919b, is monotypic. The only known species, O. parasitica G.O. Sars, 1874, is distinguishable by its long urticant organs, which bear nematocysts on their capitate tips. The position of the genus is uncertain; Stechow (1919b) and Bedot (1923) placed the genus in Kirchenpaueriidae, whereas Sars (1874, original description as Ophiodes parasitica), Allman (1883), Bonnevie (1899), and Jäderholm (1909) placed the species in Haleciidae, drawing similarities to the genus Hydrodendron Hincks, 1874. These facts led us to consider Ophinella a useless out-group for the analysis.
The genus Pycnotheca Stechow, 1919b, is characterized by the presence of an abcauline intrathecal septum (Bouillon, 1985). The genus includes two species: P. mirabilis (Allman, 1883), which is herein adopted as an outgroup of Oswaldella, and P. producta (Bale, 1882; not included as out-group). The choice of only one of the species of the genus was related to the total available information about them.
The last genus recognized as valid by Bouillon (1985) was Kirchenpaueria Jickeli, 1883, with some 20 nominal species. According to Bouillon (1985: 169; herein translated to English), it is characterized as follows “Branched or unbranched, monosiphonic or polysiphonic colonies. Hydrothecal marginal rim non-denticulated. Hydrotheca without intrathecal septum. Unforked hydrocladia. Mesial nematotheca present or not, when present either superior or inferior or in both positions”. Hence, it is clear that, at least in an essentialistic view (by now independent of a phylogenetic approach), Kirchenpaueria is mainly characterized by the lack of the diagnostic features of the other genera of the family.
Bouillon considered Ventromma Stechow, 1923 a junior synonym of Kirchenpaueria. Nevertheless, in several recent papers other authors have treated it as a valid genus (Cornelius, Manuel & Ryland, 1990; Boero & Bouillon, 1993; Vervoort, 1993; Medel & Vervoort, 1995; Migotto, 1996; Calder, 1997). We concur based on a study of the type species of both genera. It is possible to note distinct differences between them: in Ventromma, the mesial superior nematophore in the hydrothecate hydrocladial internodes is provided with a nematotheca, whereas in Kirchenpaueria that nematophore is naked. Moreover, the cauline nematophores are also provided with a nematotheca in Ventromma, whereas they are naked in Kirchenpaueria.
In conclusion, the genus Kirchenpaueria is considered a useful out-group of Oswaldella, and constitutes a unique operational taxonomic unit clearly separated from Ventromma, another useful out-group. The need for a full revision of the species of Kirchenpaueria, indeed all Kirchenpaueriidae, is clear.
Recently, a new genus, Naumovia, has been established by Stepan’yants, Peña Cantero, Sheiko & Svoboda (1997). Its only known species, N. microtheca (Naumov, 1960), is distinctively characterized by the absence of a mesial inferior nematophore in the hydrothecate hydrocladial internodes. As an additional taxon for the family Kirchenpaueriidae, in which relationships among the taxa are unknown, this genus is adopted here as an outgroup of Oswaldella.