Integrative taxonomy and phylogenetic analyses of two Ceratomyxa species (Myxozoa, Ceratomyxidae) from the China Sea, including a new species description

Two species of Ceratomyxa (Myxozoa: Ceratomyxidae) from teleosts in the China Sea are investigated using an integrative approach which combines morphological characteristcs, parasitic traits, and molecular data including small subunit ribosomal DNA (SSU rDNA) and internal transcribed spacer (ITS) regions. A novel species, Ceratomyxa dactyloptena sp. nov., was identified from the gallbladder of Oriental flying gurnard Dactyloptena orientalis Cuvier, 1829, while Ceratomyxa siganicola Zhang, Zhao, Yang & Yang, 2019 was found in the gallbladder of Mottled spinefoot Siganus fuscescens Houttuyn, 1782 and Mozambique tilapia Oreochromis mossambicus Peters, 1852.

Mature myxospores of C. dactyloptena sp. nov. exhibit a crescent shape in sutural view, with dimensions of 30.0 ± 1.3 (27.2–32.8) µm in thickness, 6.4 ± 0.4 (5.7–7.0) µm in length, and a posterior angle of 152.9 ± 3.7 ° (146.2–158.9 °). Pyriform polar capsules measured 2.9 ± 0.3 (2.3–3.3) µm long and 2.4 ± 0.3 (1.7–2.8) µm wide, with polar filaments coiled in 3–4 turns. The SSU rDNA sequence of C. dactyloptena sp. nov. was distinct from all known myxosporeans, showing the highest similarity (87.9 %) and the shortest genetic distance (0.1209) with C. filamentosi Kalatzis, Kokkari & Katharios, 2013.

Molecular analyses revealed intraspecific variation among C. siganicola strains, with ITS rDNA being more sensitive than SSU rDNA in detecting these differences. Phylogenetic analysis placed C. dactyloptena sp. nov. in a clade with C. oxycheilinae Heiniger, Gunter & Adlard, 2008, while all C. siganicola strains clustered together, forming a sister clade to C. barnesi Gunter, Whipps & Adlard, 2009. Furthermore, the phylogenetic results indicated that ceratomyxid diversification is influenced not only by host specificity but also by geographic distribution.