snail dartern. A small snail-eating darter (Percina tanasi) found only in Tennessee. A dam on the Little Tennessee River (completed in 1979) destroyed what had been the only known population of the fish, but it was later found in other locations.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.snail? dart`er n. a tan, striped, snail-eating perch, Percina tanasi, 3 in. (7.5 cm) long, found only in the Tennessee River. [1970?75] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.