A NOVEL HENNEGUYA (MYXOSPOREA) FROM THE GILLS OF GREEN SUNFISH, LEPOMIS CYANELLUS (CENTRARCHIFORMES: CENTRARCHIDAE), FROM THE BLACK RIVER (WHITE RIVER DRAINAGE) OF ARKANSAS.

A new species of genus Henneguya Thélohan, 1892 (Bivalvulida: Myxobolidae) is described from the gills of 2 of 7 (29%) green sunfish, Lepomis cyanellus (Rafinesque) from Coffee Creek of the Black River, White River drainage, Arkansas. Henneguya rafinesquei n. sp. differs from the only other species of Henneguya reported from centrarchids, Henneguya episcleraMinchew and Sleight, 1977, from Lepomis gibbosus (L.), and from Lepomis macrochirus Rafinesque by having a smaller myxospore total length (34.9 [31.3-37.1 μm] vs. 62.6 [49-81] μm). The body and polar capsules of H. rafinesquei n. sp. are pyriform, whereas the body of H. episclera is obovate to elliptical and the polar capsules are elliptoid with a narrow neck. Henneguya rafinesquei n. sp. is genetically most similar to Myxobolus branchiarumKsepka, Rash, and Bullard, 2022 from smallmouth bass, Micropterus dolomieu Lacépède, and Myxobolus lepomisRosser, Baumgartner, Barger, and Griffin, 2017 from dollar sunfish, Lepomis marginatus (Holbrook), but is easily distinguished morphologically by possessing 2 elongate caudal processes that are lacking in the latter 2 species. Phylogenetic analysis of the 1,963-base-pair small-subunit ribosomal ribonucleic acid gene placed H. rafinesquei n. sp. in a clade among other myxozoans that primarily infect centrarchids and comprises only the second species of Henneguya reported from any member of the sunfish family. Although the precise site of development within lamellae could not be determined histologically, a plasmodium with associated epithelial hyperplasia and mild lymphocytic inflammation produced a nodular lesion that displaced adjacent lamellae, altering normal gill morphology.