Myxobolus longirostris sp. n. (Myxozoa: Myxobolidae) infecting the brain of Chinese longsnout catfish Leiocassis longirostris (Günther, 1864) in China

Abstract

Abstract During an investigation of Myxobolus diversity in the Chinese longsnout catfish Leiocassis longirostris (Günther, 1864), a new species infecting the intracranial epidermis of the host was discovered. Upon opening the cranial cavity, several round whitish plasmodia measuring 0.55–0.80 mm in diameter were observed. Fresh spores (n = 50) were pyriform in the frontal view and fusiform in the sutural view, with a length of 15.4 ± 0.6 (13.9–16.5) µm, width of 9.1 ± 0.4 (8.3–9.8) µm, and thickness of 7.0 ± 0.4 (6.3–7.9) µm. The spores had smooth shell surfaces and transparent membrane sheaths in the posterior. No folds, intercapsular appendix, and caudal appendages were observed. Two equal polar capsules were pyriform and measured 7.5 ± 0.5 (6.7–8.7) µm in length and 3.2 ± 0.3 (2.5–3.6) µm in width. The polar filaments were coiled with five to six turns and perpendicular to polar capsule length. A BLAST search indicated Myxobolus longirostris sp. n. was closely related to four Myxobolus species (with sequences similarities ranging from 91.8–97.1%) found in different organs of yellow catfish Tachysurus fulvidraco, rather than the Leiocassis-infecting species M. branchiola (with 90.5% sequence similarity). Phylogenetic analysis showed that Myxobolus longirostris sp. n. clustered with M. jianlinensis and M. voremkhai within the Siluriformes-clade with highly supported values. This suggests that the host may play an important role in the evolution of Myxobolus species. Based on the morphological, ecological, and molecular differences observed between the newly discovered species and other available Myxobolus species, Myxobolus longirostris sp. n., is proposed and described in this study.