Morphological, Histological, and Molecular Description of Unicauda fimbrethilae n. sp. (Cnidaria: Myxosporea: Myxobolidae) from the Intestinal Tract of Channel Catfish Ictalurus punctatus.

The channel catfish Ictalurus punctatus is a known host for 10 species of Henneguya, but few other myxozoan genera are described from this species. Unicauda is a genus of myxozoan parasites within the family Myxobolidae that consists of 10 valid species from freshwater fish. Herein, we describe a novel species of Unicauda from the intestinal tract of farm-raised channel catfish in Mississippi. Myxospores were consistent with the genus Unicauda but exhibited a unique branching at the terminal end of the caudal process that has not previously been reported. Myxospores measured 90.39 ± 14.97 μm (mean ± SD; range = 70.88-126.02 μm) in total length. The spherical spore body measured 7.31 ± 0.26 μm (6.75-7.84 μm) in length and 7.01 ± 0.63 μm (6.1-8.01 μm) in width. The 2 polar capsules measured 3.45 ± 0.33 μm (3.02-4.03 μm) in length and 2.65 ± 0.32 μm (2.18-3.11 μm) in width. The single caudal process measured 82.98 ± 14.97 μm (63.39-118.63 μm) in length from the base of the spore body to the end of the most terminal projection. Terminal projections measured 26.83 ± 8.8 μm (12.34-42.29 μm) in length and 0.95 ± 0.23 μm (0.52-1.6 μm) in width. The 18S rRNA gene sequence obtained did not match any published sequences. Given the uniqueness of the myxospore morphology, histological presentation, and gene sequence data, we describe this as an unreported species, Unicauda fimbrethilae n. sp.