Another host, another mystery: Infection of polychaete Pista palmata (Annelida: Terebellidae) with a new blood fluke (Digenea: Aporocotylidae) in the coastal Northwest Atlantic Ocean.

Terebelliform annelids can serve as intermediate hosts for blood flukes of marine fishes and sea turtles. The scarcity of global reports on the life cycles of these parasites reflects the need for further exploration. Our objective was to further our knowledge of the diversity and life cycles of blood flukes in coastal South Carolina (SC), United States. Four species of terebellids (Enoplobranchus sanguineus, Amphitrite ornata, Pista palmata, and Streblosoma hartmanae) were collected (total N = 201) at low tide from September 2025 to February 2026 at two localities in SC. Twelve specimens of three terebellid species were infected, and parasites were identified by sequencing the LSU and ITS2 regions of ribosomal RNA and the COI mitochondrial DNA gene. Enoplobranchus sanguineus (12.9% prevalence, 4/31) and A. ornata (3.6% prevalence, 2/55) were infected with the previously reported blood flukes Neospirorchis sp. Neogen14 (Unicaecidae) and Cardicola parvus (Aporocotylidae), respectively. No specimens of S. hartmanae were infected (0/86). One new aporocotylid with mature sporocysts containing microcercous cercariae was discovered in P. palmata (20.7% prevalence, 6/29). Phylogenetic analysis revealed that sequences of the new aporocotylid were in a well-supported clade with sequences of Braya spp. and Cardicola abu. The fish host of this parasite has yet to be discovered to fully elucidate the life cycle of this new aporocotylid.