This pattern appears to be characteristic for the Opisthobranchia and Pulmonata, and it strengthens the assumption that the Euthyneura (Opistho-branchia plus Pulmonata) form a single holophyletic
group, in which the mesentoblast is formed at the 24-cell stage, distinctively earlier than in an allogastropod outgroup such as the Valvatoidea.
The genus Unionicola is considered holophyletic with the subgenus Unionicola as the least derived group.
The Unionicolinae Oudemans (Acari: Unionicolidae) represents a holophyletic group (Cook, 1974; Vidrine, 1986).
The genus Unionicola is holophyletic with the subgenus Unionicola as the least derived group.
This justification for using taxonomic data does not involve the assumption that higher taxa are "real" - by which a cladist generally means holophyletic - or that taxonomic ranks are assigned using uniform standards.
Partly for this reason, it has been suggested that we abandon traditional Linnaean taxa in favor of holophyletic taxa (e.g., Patterson and Smith 1987; Smith 1994).
Doyle and Donoghue (1993) give a hypothetical example in which patterns among lineages are not reflected by patterns in ranked taxa, even holophyletic taxa.
It has been argued that, because many of the early originating taxa are paraphyletic, and therefore have their later descendants placed in holophyletic daughter taxa, this bottom-heaviness is an artifact (e.g., Smith 1994).
Empirically, the agreement between holophyletic and paraphyletic taxa (which is quite distinct from the agreement between higher taxa and species) remains an open question.