Redescription of the Flapjack Octopod, Opisthoteuthis bruuni (Cephalopoda: Opisthoteuthidae), from the Southeastern Pacific Ocean and Evolutionary Relationships of Cirrate Octopods

ABSTRACT Cirrate octopods are considered to resemble the ancestor of all octopuses. Cirrates inhabit the deep ocean and are characterized by the presence of fins, a cartilaginous inner shell and a single row of suckers alternating with pairs of cirri thus comprising uniserial suckers and biserial cirri. The objective of this contribution is to improve the taxonomy of Opisthoteuthis bruuni from the southeastern Pacific Ocean and to suggest a new hypothesis of cirrate phylogeny. Given that the most complete molecular data set for cirrates available in public databases is comprised almost exclusively of 16S rRNA gene sequences, we compared the morphological and mitochondrial gene 16S rRNA data generated in this study from the genus Opisthoteuthis from the southeastern Pacific Ocean. Additionally, we sequenced Opisthoteuthis chathamensis, Opisthoteuthis mero and Luteuthis dentatus from the southwestern Pacific, as along with Cirroctopus mawsoni from Antarctic waters. The morphological data and the phylogenetic analysis confirm the status of Opisthoteuthis bruuni as a member of genus Opisthoteuthis and the family Opisthoteuthidae. This re-description includes the first morphological characterization of the male and female adult stage of O. bruuni, in addition to reporting geographic and bathymetric range extensions. Opisthoteuthis bruuni presents conspicuous morphological features (small terminal fins, short cirri and U-shaped shell). Our phylogenetic tree supports three families: Cirroctopodidae, Cirroteuthidae and Opisthoteuthidae, which is different from the phylogenetic arrangements previously reported.