Morphological and molecular characterization of n. sp. (Cnidaria: Myxosporea) from the bulbus arteriosus of European seabass (Teleostei: Moronidae).

A new species of Myxobolidae, n. sp., is described infecting the European seabass , a fish of high commercial value intensively cultivated in southern Europe. n. sp. was found in the bulbus arteriosus and spleen with a prevalence of infection of 13.5%. In the heart, it forms irregular whitish plasmodia measuring 1 mm in size. Mature myxospores are broadly obovoid in frontal view and ellipsoidal in lateral view, with 2 equal caudal appendages. Polar capsules are ovoid and symmetric, with 3–4 polar tubule coils. Myxospores measure 10.2 ± 0.6 (8.8–11.6) μm in length, 8.0 ± 0.7 (5.3–8.8) μm in width and 5.6 ± 0.2 (5.1–6.4) μm in thickness. Caudal appendages are 36.6 ± 3.2 (27.4–42.9) μm long. Total spore length is 47.6 ± 3.2 (41.2–53.2) μm. Polar capsules measure 4.0 ± 0.2 (3.4–4.6) by 2.2 ± 0.1 (1.9–2.6) μm. Small subunit ribosomal RNA-based tree topologies position n. sp. within a lineage of marine myxobolids that is mostly comprised of other species. Host-relatedness is reinforced as the main evolutionary driver for myxobolids, with the positioning of n. sp. further suggesting tissue tropism as another important evolutionary driver for marine heart infecting . Nonetheless, the inner complexity of this lineage suggests that identification of the evolutionary patterns driving its phylogeny will require discovery of the true diversity of marine myxobolids.