Ultrastructural aspects and molecular phylogeny of Auerbachia maamouni n. sp. (Myxosporea: Bivalvulida) from the gallbladder of Gnathanodon speciosus Forsskål (Actinopterygii: Carangidae) in the Red Sea.

A new myxosporean parasite, Auerbachia maamouni n. sp., infecting the gallbladder of the golden trevally Gnathanodon speciosus Forsskål, is described, based on morphology, ultrastructure, and small subunit (SSU) rRNA gene sequencing. Of 50 fish collected from the Red Sea in Jeddah, Saudi Arabia, five were found heavily infected with mature myxospores floating free in the bile. Mature spores are pyriform to club-shaped with smooth valves, and contain a single polar capsule with an S-shaped polar filament, arranged in 13-16 polar filament coils, oriented longitudinally, with an irregular distribution on the polar capsule matrix. Spores measure 15.8 (14-17) μm in total length in lateral view, 7.9 (6-9) μm in width in apical view, with spore body length of 6.2 ± 0.4 (5-7) µm. The ellipsoidal polar capsule has two adjusted lateral folds 7.6 (6-8) µm long and 2 (2-3) µm wide. The new species is distinguished from other species of the genus based on spore morphometry and molecular data. The phylogenetic tree constructed using Maximum Likelihood and Bayesian Inference analysis of SSU rDNA sequence data supported the phylogenetic position of A. maamouni n. sp. among the species of Auerbachia Meglitsch, 1968 sequenced to date. Analysis of the SSU rDNA sequence data also supported the assumption that Auerbachia is closely related to members of the genera Coccomyxa Léger & Hesse, 1907, Zschokkella Auerbach, 1910 and Myxidium Bütschli, 1882, whose members inhabit the gallbladder of marine teleost fishes.