Systematics of the Octopoteuthidae Berry, 1912 (Cephalopoda: Oegopsida)
Squids of the family Octopoteuthidae Berry, 1912, have been known to science for nearly 250 years and have been collected from every ocean except the Arctic and Antarctic. They are an ecologically important group, having been recorded in the diets of pinnipeds, sea birds, predatory fishes, and cetaceans, and are considered one of the most important cephalopod prey groups for sperm whales. Despite this, the family has been poorly studied due to the difficulty in identifying its species, and the diversity and systematics of the family are poorly understood. Ten formal species descriptions have been published, of which six to eight are generally recognised but only two are easily identified. Challenges to clarifying octopoteuthid systematics include the loss of important type specimens, and resolving the status of dubious taxa, potential junior synonyms, and undescribed species. No study has previously sought to resolve the systematics of the entire family.
Within this context, a global revision of the Octopoteuthidae is presented based on the examination of ~900 specimens from 12 international repositories. Extant type material was examined, and efforts made to locate previously established or suggested lost type specimens. Original descriptions and illustrations were reviewed for all historic taxa, and a critical review is given of all previously affiliated taxa. Descriptions and illustrations are provided for the 16 octopoteuthid species recognized herein, of which 10 are novel. Two genera are presently maintained within the family, Octopoteuthis and Taningia, containing 11 and 5 species, respectively. Within Octopoteuthis, four morphologic species groups were identified based primarily on photophore patterning. Descriptions are given for as much of each species’ ontogeny as material allowed, and traditional and novel morphologic characters are critically appraised in relation to their utility within the Octopoteuthidae.
A full description of the type species of the family and genus Octopoteuthis, Octopoteuthis sicula Rüppell, 1844, is given and, in light of this, Octopoteuthis danae Joubin, 1931, is considered a junior synonym. The second Atlantic species with two photophores on the posterior ventral mantle is designated Octopoteuthis megaptera (Verrill, 1885). Consistent with previous works, Octopoteuthis persica Naef, 1923, is considered a junior synonym of Taningia danae Joubin, 1931, and Octopoteuthis longiptera Akimushkin, 1963, treated as nomen dubium; the status of Octopoteuthis indica Naef, 1923 remains unresolved but is discussed. Similarly, definitive resolution of the specific status of ‘Cucioteuthis unguiculata’ (Molina, 1782) and ‘Enoploteuthis hartingii’ Verrill, 1880, could not be achieved; however, new insights were made and their implications examined.
The morphology-based review was complemented by concurrent multi-gene, phylogenetic analyses of 130 specimens from 13 of the 16 proposed species—the largest, and first targeted, genetic examination of the Octopoteuthidae. Genetic support was found for all morphologically defined species for which sequences were obtained. Intra- and interfamilial relationships are discussed based on a synthesis of genetic and morphologic data, and the formal rank of the newly recognised species groups is considered.
Octopoteuthid species were generally found to inhabit either single ocean basins or portions thereof, with several being more widely spread (usually throughout the southern hemisphere); species distributions were generally found to comprise a system of connected water currents. Inferences regarding octopoteuthid reproductive biology and spawning strategy are made based on accumulated observations during specimen examinations. Species-specific beak-to-body-size regressions were calculated for five species, and a review of known octopoteuthid predators is provided. With the recognition of their greater diversity and more defined species ranges, the evolutionary history of the family is briefly discussed.