Morphological description and phylogeny of Ceratomyxa scorpaeni n. sp. (Myxosporea: Ceratomyxidae) infecting the gallbladder of Scorpaena porcus (L.) (Scorpaeniformes: Scorpaenidae) from the bay of Bizerte in Tunisia.

A new marine myxosporean species Ceratomyxa scorpaeni n. sp. is described using morphological characteristics and small subunit ribosomal DNA (rDNA) sequence data. The parasite was found infecting the gallbladder of Scorpaena porcus Linnaeus, 1758 collected from the Bay of Bizerte. Mature plasmodia were disporous free floating in the bile. Spores were transversely elongated and crescent-shaped with unequal shell valves and measured 7.6 ± 0.2 (7.2-8.0) μm in length and 32.8 ± 0.3 (21.6-44.0) μm in thickness. Two sub-spherical polar capsules equal in size, situated at the same level and measured 3.0 ± 0.2 (3.0-3.2) μm in length and 2.4 ± 0.3 (2.3-3.3) μm in width. The infection with C. scorpaeni n. sp. was prevalent throughout the year with a maximum prevalence of infection during spring and summer. Molecular analysis of the SSU rRNA gene confirmed the parasite as a new member of the genus Ceratomyxa and showed close relationship with the species of Ceratomyxa infecting the gallbladders of Sparidae from the Mediterranean Sea. This is the first report of Ceratomyxa species from the gallbladder of S. porcus in Tunisian coastal waters.