New collections of Polylekithum from catfishes in the Big Thicket National Preserve, Texas, U.S.A., provided material for a redescription of Polylekithum catahoulensis and an evaluation of the characters used to diagnose species in the genus. The new collections demonstrated that the relative size of the forebody is not a reliable diagnostic feature of P. catahoulensis, because the feature changes linearly as worms grow; similarly, the location of the maximum width of worms is not diagnostic because it depends on the number of eggs in the uterus. However, egg size reliably distinguishes between P. catahoulensis (small eggs) and Polylekithum ictaluri (large eggs). Other morphometric and relational characteristics did not distinguish between species.