The molecular phylogeny of cirrate octopods (Cephalopoda: Octopoda: Cirrata) using COI and 16S sequences

Abstract

Contrasting accounts of taxonomic relationships between finned octopod (Octopoda: Cirrata) taxa complicate species identification and generate nomenclatural instability. A comprehensive analysis based on both 16S and COI mitochondrial gene phylogenies is presented, using all currently accepted genera and approximately 27 putative species (including type species for all genera excepting Grimpoteuthis). The goal of this is to stabilise the concepts of genera and families and identify areas needing further systematic research. Four well supported clades are consistent with families Cirroteuthidae, Cirroctopodidae, Grimpoteuthididae, and Opisthoteuthidae across both 16S and COI phylogenies. Family Stauroteuthidae resolves as a sister clade to Cirroteuthidae in some analyses of the COI gene. Combined molecular and morphological similarities suggest that the Cirrata comprises two superfamily level clades, for which Cirroteuthoidea (for Cirroteuthidae and Stauroteuthidae) and Opisthoteuthoidea (for Cirroctopodidae, Grimpoteuthididae, and Opisthoteuthidae) are proposed. The paraphyletic Cirrothauma (Cirroteuthidae) contains at least three species, while within the Grimpoteuthididae, Cryptoteuthis and Luteuthis form clades within a paraphyletic Grimpoteuthis clade, indicating a need for further taxonomic assessment. Intra-clade structure within Opisthoteuthis is better resolved with COI than 16S data. At least one potentially undescribed Opisthoteuthis occurs in the northwestern Pacific, and northeastern Pacific specimens are tentatively referred to O. bruuni, representing a significant range expansion. Lastly, using the dates of fossil stem-Octobrachians and fossil cirrates for approximate calibration, a timetree estimated from COI gene data suggests that these cirrate families and most cirrate genera arose within the Late Cretaceous, possibly as part of the Mesozoic marine revolution, between 124−62 million years ago.