A survey, conducted during May and June 2007, involving 139 specimens of Procambarus acutus from 13 localities, within the states of Louisiana, Mississippi, Tennessee, Kentucky, Illinois, Missouri, and Arkansas, U.S.A., indicated that adult Alloglossidium dolandi infected the antennal glands of crayfish inhabiting the coastal plains regions of 5 additional states. Infected crayfish were taken from roadside ditches and swamps, a lakeside wetland, and the backwater of a river. Recorded geographic distribution of the parasite was extended westward from eastern Mississippi into the Lower Mississippi River Valley. Prevalence of infection was 0% at 6 localities but ranged from 7.7% to 66.7% at 7 other localities. Comparative distribution patterns for A. dolandi and its sibling species Alloglossidium caridicolum suggest a case for allopatric speciation resulting from paleogeographic events beginning during late Pleistocene times.