The federally endangered Duskytail Darter, Etheostoma percnurum Jenkins, is known from only six highly disjunct populations in the Tennessee and Cumberland river drainages of Kentucky, Tennessee, and Virginia. Only four are extant. Variation in morphology including meristics, morphometrics, and pigmentation was examined among the four extant populations and limited specimens from the two extirpated populations (Abrams Creek and South Fork Holston River). Analyses of these data found each of the extant populations is morphologically diagnosable. The few specimens available from Abrams Creek and South Fork Holston River prevented thorough assessment of variation, and these were grouped with their closest geographic counterparts, Citico Creek, and Little River, respectively. Three new morphologically diagnosable species are described: E. sitikuense, the Citico Darter, from Citico Creek, Abrams Creek, and Tellico River (Tennessee River system); E. marmorpinnum, the Marbled Darter, from the Little River and South Fork Holston River (Tennessee River system); and E. lemniscatum, the Tuxedo Darter, from the Big South Fork (Cumberland River system). Each species warrants federal protection as an endangered species.
