Morphological and molecular characterizations of Myxobolus curriculus sp. nov. (Myxozoa, Myxobolidae) infecting the intestine of Barbel chub Squaliobarbus curriculus in China

During a myxosporean biodiversity survey in Hunan province, a novel Myxobolus species was found in the intestinal wall of Squaliobarbus curriculus. Infection was evident as numerous whitish plasmodia distributed throughout the intestinal wall, with a prevalence of 32.35 % (11 / 34). Mature myxospores were round in the valvular view, and lenticular in the sutural view, measuring 8.8 ± 0.2 (7.8–9.4) µm long, 8.3 ± 0.3 (7.5–9.3) µm wide, and 3.8 ± 0.3 (3.5–4.2) µm thick.

Two pyriform polar capsules of equal size located at the anterior end, and measured 3.8 ± 0.2 (3.5–4.3) µm long and 2.4 ± 0.3 (2.2–3.0) µm wide. The polar tubules were coiled with four to five turns. A mucous envelope and intercapsular appendix were absent, but three to four distinct posterior folds were present.

Histopathological examination indicated that plasmodia developed within the circular muscle layer of the host intestine, surrounded by a thin connective tissue capsule, and elicited no observable inflammatory response. BLASTn analysis revealed that the SSU rDNA sequence was unique, showing the highest similarity (93.02 %) to Myxobolus algonquinensis Xiao & Desser, 1997 (AF 378335), a parasite of the ovary of Notropis cornutus.

Phylogenetic construction yielded two primary clades (A and B). Within Clade A, the novel species formed a distinct sister lineage with M. dabryi, M. abitus, and M. tauricus in the subclade Ⅲ, rather than clustering with other Myxobolus species known to infect intestine.