The ink sac clouds octopod evolutionary history

Abstract

Difficulties in elucidating the evolutionary history of the octopods have arisen from problems in identifying informative morphological characters. Recent classifications have divided the largest group, the incirrate octopods, into five groups. These include the pelagic superfamily Argonautoidea and three gelatinous pelagic families (Vitreledonellidae, Bolitaenidae, Amphitretidae). All benthic incirrate octopods have been accommodated in the family Octopodidae, itself divided into four subfamilies, Octopodinae, Eledoninae, Bathypolypodinae and Graneledoninae, which are defined by the presence or absence of an ink sac, and uniserial or biserial sucker arrangements on the arms. We used relaxed clock models in a Bayesian framework and maximum likelihood methods to analyse three nuclear and four mitochondrial genes of representatives from each of the previous subfamilies. Strong evidence indicates that the family Octopodidae is paraphyletic and contains the gelatinous pelagic families. The subfamilies of Octopodidae recognised in earlier works do not reflect evolutionary history. The following clades were supported in all analyses: (1) Eledone/Aphrodoctopus, (2) Callistoctopus/Grimpella/Macroctopus/Scaeurgus, (3) Abdopus/Ameloctopus/Amphioctopus/Cistopus/Hapalochlaena/Octopus, (4) Enteroctopus/Muusoctopus/Vulcanoctopus, (5) Vitreledonella/Japetella, (6) Southern Ocean endemic and deep-sea taxa with uniserial suckers. These clades form the basis for a suite of taxa assigned family taxonomic rank: Amphitretidae, Bathypolypodidae, Eledonidae, Enteroctopodidae, Megaleledonidae and Octopodidae sensu nov. They are placed within the superfamily Octopodoidea.