A Faunistic Revision of Longnose Skates of the Genus Dipturus (Rajiformes: Rajidae) from the Southern Southwestern Atlantic Ocean, Based on Morphological and Molecular Evidence

Abstract

Abstract: The identity of longnose skates (Dipturus-Zearaja-like skates) in the southern cone of the Americas has been a topic of extensive debate. This study employs a comprehensive analysis encompassing morphometrics, claspers, and the examination of COI and NADH2 sequence data to conclusively demonstrate the existence of only two longnose skate species in the southwestern Atlantic Ocean, extending south of 35 ◦S. Notably, Dipturus argentinensis Díaz de Astarloa, Mabragaña, Hanner and Figueroa, 2008 is revealed as a junior synonym of D. trachyderma (Krefft and Stehmann, 1975). Dipturus leptocaudus (Krefft and Stehmann, 1975) remains a northern valid species, but the specimen from the Falkland Islands (Malvinas) is recognized as a misidentification of D. trachyderma. Zearaja flavirostris (Philippi, 1892) and Dipturus lamillai Concha, Caira, Ebert and Pompert, 2019 are confirmed as junior synonyms of Zearaja brevicaudata (Marini, 1933). These findings contradict the previous report of six species within the same region over the last decade and underscore the presence of D. trachyderma and Z. brevicaudata south of 35 ◦S in the southwestern Atlantic. Additionally, this study notes the occurrence of only one specimen of Z. chilensis (Guichenot, 1848) in the Falkland Islands (Malvinas), suggesting an unusual frequency of this eastern Pacific skate in the southern Southwest Atlantic. Given that clasper morphology serves as the key distinguishing trait between Dipturus and Zearaja species, we provided a detailed analysis of the clasper characteristics of the Atlantic D. trachyderma, unequivocally situating it within Dipturus. The diagnostic characteristics include: (i) the presence of cartilage with the distal portion referred to as the sentinel, a feature absent in Zearaja; (ii) longer ventral terminal cartilage with the distal end referred to as the funnel, compared to Zearaja; and (iii) a non-spatulate distal lobe, a distinctive trait specific to Dipturus.