Taxonomy and phylogeny of Myxobolus branchiostegi sp. nov. (Myxozoa, Myxosporea) infecting the gallbladder of Branchiostegus argentatus Cuvier, 1830 from the East China Sea

Myxobolus branchiostegi sp. nov. was detected in the gallbladder of six out of 28 specimens (21.4%) of Branchiostegus argentatus Cuvier, 1830 from the East China Sea. This is the first record of a Myxobolus species infecting this host. Mature myxospores of the new species were oval in valvular view, measuring 9.21 ± 0.52 µm (8.3–9.8 µm) in length and 7.40 ± 0.60 µm (6.2–8.0 µm) in width. Two equal, pyriform polar capsules measured 4.40 ± 0.34 µm (3.7–4.8 µm) in length and 2.58 ± 0.17 µm (2.3–2.9 µm) in width, each possessing polar tubules with 4–6 turns. Phylogenetic analysis, based on small subunit ribosomal RNA gene (SSU rDNA) sequences placed the new species within the family Myxobolidae, as a sister to Myxobolus iwagiensis Kawano et al., 2025. Further analysis suggested a possible trend that the clustering of Myxobolidae species may be influenced by the taxonomic affinity of their fish hosts, with closely-related parasites tending to infect hosts within the same order. Host aquatic habitat (marine, brackish-water or freshwater) and species geographic distribution may also contribute to the observed clustering patterns.