Morphological identification of two southwest Atlantic loliginid squids: Loligo gahi and Loligo sanpaulensis

Abstract

Morphological characters of two loliginid squids, Loligo gahi and Loligo sanpaulensis, in the SW Atlantic region off Argentina were studied to obtain a diagnostic criterion for their identification. Emphasis was placed on the taxonomic characters suitable to identify individuals in the whole size range. Considering the uncertainty associated to the correct identification of juveniles, their taxonomic status was confirmed using electrophoretic studies. Discrimination between species based on morphological characters proved to be more effective than meristic counts. A discriminant function that allows an easy separation of the two species is presented. The function, composed of two indices: fin width mantle length (FW/ML)and gladius width mantle length (GW/ML)allows to identify a specimen as L. gahi with a 100. and L. sanpaulensis with a 97. probability of correct classification. FW/ML can be used alone as a rapid differentiation tool. In general, index values lower than 0.53 correspond to L. gahi and those higher to L. sanpaulensis. In fresh specimens, the chromatophore pattern on the oral face of arms IV also provides useful information to distinguish between the two species.