New marine leech species of Branchellion Savigny, 1822 (Hirudinida: Piscicolidae) and new host record of Pontobdella muricata in the Gulf of Tunis

Studies of Hirudinea species infesting elasmobranchs are scarce and scattered worldwide and they are inexistent off the Tunisian waters. In this work, we aimed to assess the occurrence of these parasites on two ray species in the Gulf of Tunis (Tunisia). Between 2017 and 2021, 254 fish specimens belonging to two Torpedinidae species (marbled electric ray, Torpedo marmorata Risso, 1810, and common torpedo, Torpedo torpedo (Linnaeus, 1758)) were examined for leech infestation. Morphological and molecular characterizations based on 18S rDNA and cytochrome c oxidase (COI) sequences allowed us to identify two leech species: Pontobdella muricata (Linnaeus, 1758) and a new Branchellion Savigny, 1822 species Branchellion tunisensis sp. n. This new species (B. tunisensis) exhibited distinctive traits unlike other Branchellion, including a transparent body marred with dark green along the abdomen and neck, long trachelosome (about 1/3 of the length of the body), distinctive two eye spots, the presence of a pair of lateral branchiae per somite except for the last 2 somites and cup-shaped posterior sucker. Molecular analysis of the 18S rDNA and COI gene fragments shows more than 10