Taxonomic considerations of squids of the family Loliginidae (Cephalopoda: Myopsida) supported by morphological, morphometric, and molecular data

The taxonomy of squids in the family Loliginidae Lesueur, 1821 is complicated due to their inconsistent descriptions which hamper identification at the species level. In this study, a taxonomic revision of loliginid squids from the northwestern Atlantic was carried out considering morphological, molecular, and morphometric characteristics. Squid were collected in four oceanographic cruises along the coast of Tamaulipas, Gulf of Mexico during the period of 2012 to 2014. Museum (NMNH) specimens (type and non-type material) of the species reported for this area were also considered. The morphological attributes described for each species allowed us to confirm the identity of Doryteuthis pealeii (Lesueur, 1821), Lolliguncula brevis (Blainville, 1823), and males of Doryteuthis pleii (Blainville, 1823); the identification of females of D. pleii and Doryteuthis roperi (Cohen, 1976) (the latter only represented by museum material) was not achieved because of the high interspecific similarity. Three genetic clades were detected with COI sequences associated with each of the three field-collected species that were identified morphologically, including the unidentified females, which were recognized as D. pleii. The morphometry of these three groups was addressed by canonical variate analysis, which supported the interspecific differences. A multivariate analysis of variance was conducted for D. roperi and D. pleii due to their high level of morphological similarity. This analysis indicated significant differences; therefore, it did not allow to confirm if D. roperi is a synonym of D. pleii.