The morphological and molecular characterization of Myxobolus khaliji n. sp. (Myxozoa: Myxosporea) from the double bar seabream Acanthopagrus bifasciatus (Forsskål, 1775) in the Arabian Gulf, Saudi Arabia.

Myxobolus khaliji n. sp., a new myxosporean, is described from the intestinal wall of the double bar seabream Acanthopagrus bifasciatus, collected from the Arabian Gulf off the coast of Saudi Arabia. It is characterized by the presence of ellipsoidal or round plasmodia of 2-4 mm in diameter. Mature spores were subspherical to elliptical in the frontal view, with a slightly pointed anterior end and a bluntly rounded posterior end, and measured 8.1 ± 0.4 (7.2-9.5) μm long, 6.3 ± 0.6 (5.1-7.4) μm wide, and 9.2 ± 0.7 (8.3-10.2) thick. Spore valves are relatively thin, sometimes with a prominent thick caudal appendage. Two equal elliptical polar capsules were situated in the plane of the suture line at the anterior end of the spores and occupied above half of the spore length. Polar capsules measured 5.5 ± 0.7 (4.1-6.1) μm long and 3.2 ± 0.2 (2.1-4.2) μm wide. Polar filaments, wound in three to four coils, were situated perpendicularly to the longitudinal axis of the polar capsules. Combining the morphological characteristics, host specificity and geographical distribution, tissue tropism, and the molecular analysis of the partial sequence of the SSU ribosomal DNA gene, it was concluded that M. khaliji n. sp. was distinct from all previously described Myxobolus species. Phylogenetic analysis placed the present Myxobolus species in a marine Henneguya clade, which is a sister group of marine Myxobolus species. This is the first Myxobolus species with Henneguya-like spores from the marine environment to be found in the Saudi Arabian coasts of the Arabian Gulf.