The oegopsid squid family Onychoteuthidae presently comprises six genera (Moroteuthis, Onychoteuthis, Ancistroteuthis, Kondakovia, Onykia and Chaunoteuthis) but the status of some of these is still uncertain. An interdisciplinary study was undertaken to clarify the phylogenetic relationships, which included a morphological approach (morphometric analysis), and a molecular study of a mitochondrial gene portion (l–rRNA gene, 16S).
The morphometric analysis identified two groups, one including some Onychoteuthis and some Moroteuthis knipovitchi, and another including the remaining genera or species. At the intrageneric level, M. knipovitchi appears to be separated from the other species of the genus; M. robusta is closely related to M. ingens and M. pacifica. Morphometric analysis confirmed that Kondakovia longimana is different from M. ingens. Likewise, Onychoteuthis was clearly separated from the other genera, but there is neither geographical grouping nor morphometric differentiation of the Onychoteuthis species with the parameters measured. Some specimens were apparently intermediate between the Onychoteuthis and Ancistroteuthis groups.
On a molecular basis, the Onychoteuthidae appeared to be monophyletic. Monophyly of the genus Moroteuthis (four species studied) was not strongly supported: M. knipovitchi was distinct from the others. The molecular analysis showed three Hawaiian species, Onychoteuthis compacta, O. sp. B and O. sp. C, to be closely related. The gene sequence for the newly created species of Onykia is clearly different from all the others, indicating that it is a true species.