Morphology, seasonality and phylogeny of Zschokkella trachini n. sp. (Myxozoa, Myxosporea) infecting the gallbladder of greater weever Trachinus draco (L.) from Tunisian waters.

We describe a new myxosporean species, Zschokkella trachini n. sp., infecting the gallbladder of greater weever Trachinus draco Linnaeus 1758 from Tunisia. This is the first record of Zschokkella species in T. draco. Plasmodia were polysporic producing six to eight mature spores; they were attached to the gallbladder epithelium or free floating in the bile. Mature spores were sub-ovoid in the frontal view, measured 15.2 ± 0.6 (14.4-16.0) μm in length and 9.8 ± 0.7 (9.0-10.8) μm in width. Two equal spherical polar capsules 4.0 ± 0.4 (3.6-4.5) μm in diameter, were located separately at the spore's extremities. The prevalence of infection ranged from 23.5 to 87.7 %. Morphological data and molecular analysis of the small subunit rDNA gene identified this parasite as a new species of Zschokkella. Neighbour joining clustered the parasite in a sub-clade containing other Zschokkella species parasiting the gallbladder of marine fish hosts, located within the coelozoic clade of the major freshwater clade. This is the second Zschokkella species reported from Tunisia.