Is There a Third Species of the Genus Squalus (Squalidae) Present in the Marmara Sea, or Just an Extreme Case of Intraspecific Variability of Squalus blainville?

On 21 February 2024, 12 neonate spurdogs (Squaliformes: Squalidae) were captured with a bottom trawl towed over a sandy-muddy bottom at depths of 121–126 m in the eastern sector of the Marmara Sea. Eleven out of 12 spurdogs were identified as Squalus blainville (Risso, 1827), but one of the spurdogs, specimen MD6-24-SquaSp, exhibited several characteristics of both S. blainville and S. megalops. The results of this study suggest two possibilities: (1) either S. blainville shows a significant degree of intraspecific variability, and therefore, there is a highly differentiated variety of S. blainville that may occur in the Marmara Sea, or (2) there is a yet undescribed species belonging to the S. megalops clade that occurs in the region. This uncertainty supports the need for a genetically based taxonomic revision of the species of the genus Squalus in the Marmara Sea.