Heteromicrocotyla polyorchis Unnithan, 1961 (Monogenea: Heteromicrocotylidae), a gill parasite of the yellow-spotted trevally, Carangoides fulvoguttatus (Carangidae) from Saudi Arabia: Morphology and phylogeny.

Little information for parasitic infections of Carangoides fulvoguttatus was recorded. The present study was intended to investigate the gill parasite Heteromicrocotyla polyorchis of this fish and to provide a full morphological description and clarify its taxonomic status through phylogenetic analysis of the 28S rRNA gene region. A total of sixty fish specimens have been collected from the studied area (the Red Sea in Jeddah Province, Saudi Arabia) and gills were isolated and examined for identification of parasites. Using light electron microscopy, the recovered monogenean parasite's morphology was exhaustively characterized and described. Microscope examinations found that this parasite species represent Heteromicrocotyla polyorchis, and it could be distinguished from congeners of the same genus by armed genital atrium and cirrus sac, follicular post-ovarian testes, unique shape and number of clamps on both haptor sides, and the dorsally curved tip of the male copulatory organ. Morphological features were combined with molecular analysis of the 28S rRNA gene region. The selected gene for the isolated Heteromicrocotyla species was analyzed using appropriate primers to assist in phylogeny with those in the GenBank database. The present monogenean species was characterized by unique genetic sequences that were analyzed and deposited in the GenBank for the first time under the accession number MW406473. Phylogenetic analyses reported that the maximum identity between the current Heteromicrocotyla species and taxa of Heteromicrocotylidae was between 91.42 and 92.09% and confirmed its taxonomic status in this family with a well-distinct clade. The present study supported the second report of H. polyorchis as carangid fish ectoparasites and investigates the first appearance in C. fulvoguttatus inhabiting Saudi Arabia.