New freshwater Ceratomyxa species, Ceratomyxa schwanefeldii n. sp. (Myxozoa: Ceratomyxidae) from the gall bladder of tinfoil barb, Barbonymus schwanefeldii (Cyprinidae, Cypriniformes) in Malaysia.

Genus Ceratomyxa comprises coelozoic parasites of mainly marine and brackish water fish. This study describes a new Ceratomyxa species, Ceratomyxa schwanefeldii n. sp. which parasitizes the gall bladder of Barbonymus schwanefeldii collected from Sungai Tong in Setiu, Terengganu, Malaysia. The new species was described using morphological characteristics, and on nucleotide sequences of small subunit ribosomal DNA (SSU rDNA) and large subunit ribosomal DNA (LSU rDNA). Ceratomyxa schwanefeldii n. sp. exhibited vermiform shape plasmodia with slow undulatory motility, measuring 151.6 ± 86.0 (43.0-271.0) μm in length and 15.1 ± 4.8 (9.3-22.7) μm in width, with blunt poles at both ends. The mature spores were crescent-shaped, strongly arched in frontal view, with a sutural line between the two valves tapering to blunt ends. Formalin-fixed spores were 3.0 ± 0.4 (2.4-3.9) μm in length, 12.6 ± 1.2 (10.8-15.4) μm in thickness, with a concave posterior angle, 104.8° ± 10.2° (73.4-123.8). Two equal-sized spheroid polar capsules measured 1.5 ± 0.2 (1.2-1.8) μm in length and 1.3 ± 0.2 (0.9-1.7) μm in width. Phylogenetic analyses by Maximum likelihood and Bayesian Inference algorithms positioned C. schwanefeldii n. sp. as a sister species to Unicapsulocaudum mugilum and clustered within the clade of Amazonian freshwater Ceratomyxa species. The LSU rDNA phylogeny revealed that C. schwanefeldii n. sp. clusters within the marine Ceratomyxa clade and forms a sister relationship with C. leatherjacketi. This study represents the first description of a freshwater Ceratomyxa in Malaysia and the fourth recorded detection in the Asian region.