The role of invertebrate hosts in some acanthocephalan life cycles is unclear because juveniles are difficult to identify to species using morphology. The turtle acanthocephalan, Neoechinorhynchus emydis, has been reported in ostracod and snail hosts. However, the role these hosts play in the life cycle is unknown. To better elucidate the role of ostracods and snails, we collected 558 snails of 2 species and 37,208 ostracods of 4 species in Oklahoma and examined them for infections. Juvenile acanthocephalans were morphologically and molecularly characterized, using the ITS region of parasite rDNA. We also sampled turtle definitive hosts to compare sequences of adult to juvenile acanthocephalans. Of the 23 locations sampled for snails, 7 (30%) were positive for juvenile acanthocephalans. Overall prevalence of acanthocephalans in the snails Planorbella trivolvis and Physa acuta was 20% and 2%, respectively. In contrast, only 1 species of ostracod (Physocypria sp. morphotype 1) was infected, with an overall prevalence of 0.1%. Although 4 species of acanthocephalans infected turtle definitive hosts, all the ITS sequences from juveniles infecting snail hosts were conspecific with N. emydis. In contrast, the ITS sequences from juvenile acanthocephalans from ostracods were conspecific with 2 species of acanthocephalans from turtles, N. emydis and N. pseudemydis, and 1 species of acanthocephalan from fish (N. cylindratus). These results indicate that N. emydis commonly infects freshwater snails, whereas other species of Neoechinorhynchus appear not to infect snail hosts.