Morphological, Molecular and Phylogenetic Characterization of Auerbachia megacapsula n. sp. (Myxozoa: Coccomyxidae) from Larimichthys crocea Richardson, 1846

Purpose

This study describes a novel myxosporean species, Auerbachia megacapsula n. sp., isolated from the gallbladders of Larimichthys crocea Richardson, 1846 from the South China Sea.

Methods

The morphometry and morphological studies were carried out using Nikon Ni-U microscope. Molecular analysis, phylogenetic reconstruction, molecular clock estimation, and cophylogenetic inference based on small subunit ribosomal DNA (SSU rDNA) sequences, were performed using appropriate softwares.

Results

The myxospores were characterized by their club-shaped morphology, with a broader anterior region and a less prominent posterior extension. In the side view, the sutural line was indistinct, with the smooth, asymmetrical valves jointed at the edge. Mature myxospores measured 22.2 ± 1.7 (15.9–25.5) µm in length and 12.8 ± 0.9 (11.4–14.3) µm in width. The polar capsule was 18.9 ± 1.4 (14.1–20.5) µm in length and 4.7 ± 0.3 (3.6–5.0) µm in width, with polar tubules coiled 2–4 turns, reaching a total length of 83.3 ± 1.5 (82.2–84.4) µm. Molecular analysis based on SSU rDNA revealed that the species shares the highest similarity of 98.3% with Auerbachia chaetodoni, supporting its novelty. Phylogenetic analysis showed that this species occupies a basal position within the main Auerbachia clade.

Conclusion

The integration of morphological, molecular, and phylogenetic evidence, together with distinct host specificity and geographic distribution, supports the recognition of Auerbachia megacapsula n. sp. as a novel species within the family Coccomyxidae.