A new species of darter has been described from the upper Tennessee River drainage.
The description by Lawrence Page and Thomas Near, is published in the latest issue of the journal Copeia.
The new species, named Percina williamsi after James D. Williams and given the common name of Sickle Darter, is most closely related to the Longhead Darter, P. macrocephala.
Percina williamsi shares with P. macrocephala the presence of a sickle-shaped suborbital bar and a black bar subtending a median black spot on the caudal-fin base, characters which distinguishthe two species from all other members of the genus.
Percina williamsi is separated from P. macrocephala in having larger scales, including usually 24"26 scales around the caudal peduncle, 21"23 transverse scales and 70"77 lateral scales.
On average, P. williamsi also has a shorter snout than P. macrocephala. Analyzing the complete cytochrome b sequence (a mitochondrial gene), the authors confirm that the two species are distinct and that P. williamsi and P. macrocephala diverged from a common ancestor about 2.3 million years ago.
According to the authors, Percina willamsi lives in flowing pools over rocky, sandy, or silty substrates in clear creeks or small rivers...It is found most often near woody debris, vegetation such as water willow, or large boulders....As its fusiform shape suggests, it spends most of its time swimming in current in the water column...
For more information, see the paper: Page, LM & TJ Near (2007) A new darter from the upper Tennessee River drainage related to Percina macrocephala (Percidae: Etheostomatinae). Copeia 2007, 605"613.