Octopus americanus: a cryptic species of the O. vulgaris species complex redescribed from the Caribbean

17 pages, 4 tables, 8 figuresThe common octopus Octopus vulgaris Cuvier, 1797, once considered a cosmopolitan species, is a species complex composed by six species: O. tetricus, O. cf tetricus and O. sinensis in the Pacific; type I and II, in the West Atlantic; and type III in the Indian Ocean around South Africa. The tropical western central Atlantic is an important octopus fishing ground targeting O. maya, O. insularis, and a cryptic species considered to be O. vulgaris type I. In order to clarify the identification of this octopod, phylogenetic analyses were carried out with mitochondrial (COI and 16S) and nuclear (rhodopsin) genes, together with morphological analyses of 16 specimens caught in the northeastern continental shelf of Yucatan (Mexico). The main morphological traits differing from O. vulgaris were the presence, position and size of enlarged suckers and hectocotylus sucker number in males. Genetic distances and haplotype networks of the species complex were estimated using 285 COI sequences of nine Octopus species from 14 different locations around the world. The octopod sequences from Yucatan clustered within a monophyletic group that included sequences of O. vulgaris type II for the three genes analyzed. Phylogenetic distances with other members of the complex ranged between 2.71 and 3.89% using COI data. These genetic results support the presence of Octopus americanus Monfort, 1802 (formerly known as O. vulgaris type II) along the Yucatan continental shelf, a new octopod extending from the north of Argentina to the northwest coast of the USAThe results of this study were obtained as part of the project “Distribution, reproduction, biomass and movement patterns of the Octopus vulgaris common octopus, Cuvier 1797, on the Yucatan coast” with funding from the National Council of Science and Technology of Mexico (CONACyT) (No. 237057). This work was partially supported by the Project CALECO (CTM2015-69519-R) funded by the Spanish Ministry of Economy and Competitiveness and FEDER FundsPeer reviewe