Redescription of Myxidium sphaericum Thelohan, 1895 and Ceratomyxa beloneae Lubat et al., 1989 from the gall bladder of the garpike, Belone belone in the Adriatic Sea

The garpike Belone belone (L.) is an epipelagic fish abundant in the Mediterranean, parasitized by two coelozoic myxosporidians in the gall bladder — Myxidium sphaericum Thélohan, 1895 and Ceratomyxa beloneae Lubat, Radujković, Marques et Bouix, 1989. In order to redescribe these intriguing and taxonomically complex species, whose original descriptions are limited only to line drawings based on light microscopy, we studied the morphology and ultrastructure of their vegetative and sporogenic stages. M. sphaericum has an oval to sigmoid or mild crescent shape in the frontal view, large conical polar capsules, opening at the spore end, in opposite direction of the spore length, with 8–9 coils of polar filament. C. beloneae has elongated and slightly arched valves; symmetrical and smooth, with the posterior surface almost straight and anterior surface mildly inclinated, having 5 coils of the polar filament.