Species of the genus Octopus from the northeastern Pacific are ecologically and economically important; however, their taxonomy is confusing and has not been comprehensively assessed. In this study, we performed a taxonomic evaluation of these species considering the morphological characteristics of the original descriptions, a molecular analysis of partial COI-gene sequences, and a traditional morphometry analysis of nine body measurements. Several interesting findings were obtained with our results: for instance, we updated the diagnoses of some species by including characters such as the number of lamellae per demibranch and the presence of chromatophores in the visceral sac; we deposited partial COI-gene sequences of species that had not been incorporated into the GenBank repository; and according to the morphometric analysis, we confirmed that the lengths of arms I–IV are relevant to discriminate the species under study. The taxa evaluated were morphologically, molecularly and morphometrically well-delimited; however, features such as funnel organ shape and arm length proportions in regard to dorsal mantle length are either not included in the diagnosis of the genus Octopus or overlap with other genera. Hence, this information, combined with the results obtained from the molecular analysis, supports the generic re-assignation of two of the species evaluated.

Understanding the feeding habits of the Mexican barracuda, Sphyraena ensis Jordan and Gilbert, 1882, is important to elucidate relevant aspects of its trophic ecology (prey intake, diet breadth, trophic level, and energy flows), which in general provide valuable information on the dynamics of marine communities. Therefore, the purpose of this work was to assess the dietary habits of the Mexican barracuda, S. ensis, and to determine dietary variations by sex (males, females), size (small, medium, and large individuals), and season (rainy and dry). Monthly samples were obtained from February 2014 to January 2015 in the San Blas region, Nayarit, Mexico. A total of 308 specimens were captured. Individuals measured between 30.6 and 58.7 cm total length and weighed between 405 and 836 g. Of the analyzed stomachs, 264 (86%) contained food and 44 (14%) were empty. The diet of the Mexican barracuda comprised 13 prey items from 11 families, 12 genera, and 9 species. According to the index of relative importance, the most important prey were fishes, particularly Sardinops spp. (40.36%), Hemiramphus saltator (40.24%), Opisthopterus dovii (10.83%), Anchoa spp. (4.17%), and Mugil cephalus (3.05%). We conclude that the Mexican barracuda can be categorized as an opportunistic ichthyophagous predator in coastal epipelagic zones that feeds mainly on schooling fish species. The trophic spectrum did not vary significantly by sex or size, but the consumption of preferred prey varied significantly by season.

Cephalopods have upper and lower chitinous beaks, and their shape can be used to identify species. However, the morphological attributes of beaks are commonly obtained from sources that contain little information on shape, compromising the determination of taxa. Thus, in this study, we used geometric morphometrics to analyze inter-specific differences in beak shape of six octopus species from the northeastern Pacific. We found evidence of species-level discrimination according to upper and lower beak shape. In addition, we provided a detailed description of these chitinous structures for each species, and we developed a key to identify the species based on upper and lower beak shape. The inter-specific morphological variation of beaks of the octopuses evaluated in our study could be the result of adaptive processes related to habitat and feeding habits. The information generated in our study can be used for identification of six octopus species from the northeastern Pacific based on upper and lower beak shape.

Loliginid squids from the northeastern Pacific are partially sympatric, and their identification is difficult as their diagnostic characters often overlap. Statoliths are hard structures that may vary with respect to phylogeny and thus have potential use in taxonomy. This, however, has to be investigated using robust methods. Here, we employ geometric morphometrics to evaluate the taxonomic utility of statolith shape in loliginids caught in Mexican waters and to acquire knowledge on statolith evolution through comparative phylogenetic methods. The loliginid species we examined showed specific statolith morphology that facilitates species identification. Our results also show that statolith shape has a strong phylogenetic signal and is a powerful character for species recognition. The ancestral statolith morphologies are not very different from extant forms, probably reflecting the relatively recent origin of the two genera evaluated and their low evolutionary rate. In addition, the evolution of statolith shape in species of the genus Lolliguncula seems to have been faster than that in the genus Doryteuthis, especially in L. panamensis, which could be related to habitat differentiation in the neritic coastal environment inhabited by loliginid squids. Our analysis of statolith shape demonstrates the potential for combining neontology and paleontology in understanding the diversification of loliginid squids.