Taxonomic assessment of species of the genus Octopus from the northeastern Pacific via morphological, molecular and morphometric analyses.

Mariana Díaz-Santana-Iturrios,César Augusto Salinas-Zavala,Jasmín Granados-Amores,Francisco Javier García-Rodríguez

doi:10.7717/peerj.8118

Abstract

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.

Highlights

Octopuses are important marine resources worldwide; their taxonomy is complicated (Norman & Hochberg, 2005; FAO, 2016)
In this study we evaluated the species-level assignment of octopuses from the northeastern Pacific using morphological, molecular, and morphometric criteria
The proportion of arm length in regard to dorsal mantle length (DML) is relevant to discriminate the species evaluated in this research, and this feature resulted ambiguous for Octopus according to our analysis, it supports that O. alecto belongs to the genus Paroctopus and that O. californicus (2–3.5 times DML) belongs to a genus different from Octopus within the family Enteroctopodidae, further studies should be performed to formalize their respective novel combinations

Summary

Introduction

Octopuses are important marine resources worldwide; their taxonomy is complicated (Norman & Hochberg, 2005; FAO, 2016). Similar to the rest of cephalopods and most animal species, the taxonomy of the genus Octopus is fixed on the basis of morphological and meristic attributes of body parts For species of this genus, the relevant characters include: number of gill lamella, funnel organ shape, presence or absence of ocelli, among others (Verrill, 1883; Pickford & McConnaughey, 1949; Berry, 1953). In many species (e.g., confusion between Octopus insularis Leite & Haimovici, 2008 and Octopus vulgaris Cuvier, 1797, see Lima et al (2017)), the morphological traits are not well-delineated and this hinders their identification To increase this problematic, any species with an ink sac and arms in a two-row sucker arrangement is catalogued within the genus, and despite that these two characters are considered diagnostic for Octopus, these attributes are detected in other genera of the family Octopodidae (Cuvier, 1797; Guzik, Norman & Crozier, 2005; Strugnell et al, 2014; Jereb et al, 2016). The milestone of the taxonomic complexity of the genus Octopus is the type species of this taxon, Octopus vulgaris, which comprises a complex of morphologically similar but genetically distinct species catalogued in types (Amor et al, 2019)

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Discussion

Conclusion