Comments: Placed in the genus Pagophilus by Muizon (1982), Rice (1998), Baker et al. (2003), and some other authors, but regarded (with the nominal genera Histriophoca and Pusa) as a member of the genus Phoca in other recent literature (e.g., King 1983; Riedman 1990; Nowak 1991; Reeves et al. 1992; Wozencraft, in Wilson and Reeder 1993).
A cladistic analysis of mtDNA data yielded three clades among northern seals: Phoca-Pusa-Halichoerus, Cystophora-Pagophilus, and Erignathus (Perry et al. 1995). Each clade may be regarded as a tribe of the subfamily Phocinae. The magnitude of the differences among Phoca, Pusa, and Halichoerus was on the same order as that between species and subspecies within the genus Odocoileus. Because Cystophora is the closest relative of Pagophilus, the latter cannot be regarded as congeneric with Phoca; the differences between the two are great enough to justify placing them in separate genera (Perry et al. 1995). However, Mouchaty et al. (1995) examined the mitochondrial cytochrome b gene and found a close relationship between P. groenlandicus and Histriophoca fasciata, which, they noted, merits further study.