Two new species of Scalithrium (Cestoda: Rhinebothriidea) from rajiform batoids of the Argentine Sea

Abstract

Two new species of Scalithrium Ball, Neifar & Euzet, 2003 were found in rajiform batoids of the Argentine Sea: Scalithrium kirchneri sp. nov., parasite of the Rio skate Rioraja agassizii (Müller & Henle) from waters off Buenos Aires Province, and Scalithrium ivanovae sp. nov., parasite of the La Plata skate Atlantoraja platana (Günther) from waters off Río Negro Province. Scalithrium kirchneri sp. nov. and S. ivanovae sp. nov. differ from their congeners by having a particular combination of features including: total length, number of loculi on the distal bothridial surface, absence of bilobed bothridia and number of testes. Additionally, S. kirchneri sp. nov. can be distinguished from S. ivanovae sp. nov. by the presence of a vaginal sphincter and seminal receptacle, by the position of the entrance of the vas deferens into the cirrus sac, and by the microthrix pattern on the proximal bothridial surface. Based on this and previous studies, we conclude that some morphological traits may not be considered as key characters for the generic diagnosis of Scalithrium due to their variability within the genus. These characters include the musculature disposition in bothridial transverse septa and position of the entrance of the vas deferens into the cirrus sac, which certainly complement other diagnostic characters at a specific level. The discovery of these two species represents the first record of the genus Scalithrium in temperate waters of the Southern Hemisphere. In addition, this study is the first to undoubtedly identify batoids from the order Rajiformes as hosts for Scalithrium.