Morphological and molecular characterization of <i>Henneguya cystigena</i> n. sp. (Cnidaria, Myxosporea) parasitizing the alimentary tract of yellowfin seabream, <i>Acanthopagrus latus</i>, in the East China Sea

A novel myxosporean species was identified. The species formed spherical to ellipsoidal pseudocysts within the alimentary tract wall of a yellowfin seabream Acanthopagrus latus fished in the East China Sea. Histological examination confirmed that pseudocysts were localized within the submucosal layer of the stomach wall. Round to ellipsoidal myxospores exhibited two posterior caudal appendages, consistent with the morphological characteristics of the genus Henneguya. The myxospore body measured 9.6 ± 0.5 (8.6-10.6) μm in length, 7.3 ± 0.4 (6.8-7.9) μm in width, and 6.0 ± 0.2 (5.5-6.4) μm in thickness. Two equal pyriform polar capsules were observed, measuring 3.5 ± 0.3 (2.9-4.4) μm × 1.9 ± 0.2 (1.4-2.2) μm. Pairwise comparison referring to small subunit ribosomal DNA sequence revealed a highest identity of 94.19% with Henneguya yokoyamai Li et al., 2012, supporting the classification of the specimens as a new species, Henneguya cystigena n. sp. Phylogenetic analyses demonstrated intermixed groupings of myxobolid species, highlighting persistent discrepancies between traditional morphological taxonomy and increasingly refined molecular phylogeny. To the best of our knowledge, this study represents the first description of a Henneguya species parasitizing a marine fish in the East China Sea near mainland China.