Systematic revision of the genus Orchidasma and description of Orchidasma orchilobata n. sp. from the loggerhead (Caretta caretta) and Kemp’s ridley turtle (Lepidochelys kempii)

Authors: ROSSER, THOMAS - Mississippi State University; MEAUX, AIDEN - Mississippi State University; WOODYARD, ETHAN - Mississippi State University; STILWELL, JUSTIN - Mississippi State University; Richardson, Bradley; ROBISON, LOGAN - Mississippi State University; HUDNALL, JILL - Mississippi State University; MCNULTY, KAYLIN - Mississippi State University; NGUYEN, JONAH - Mississippi State University; ROSE, DIVYA - Mississippi State University; MOORE, DEBRA - Mississippi State University; PETERMAN, BETH - Mississippi State University; REICHLEY, STEPHEN - Mississippi State University; LAWRENCE, MARK - Mississippi State University

Submitted to: Systematic Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/2025
Publication Date: 6/30/2025
Citation: Rosser, T.G., Meaux, A., Woodyard, E., Stilwell, J.M., Richardson, B.M., Robison, L.R., Hudnall, J.B., Mcnulty, K., Nguyen, J.A., Rose, D., Moore, D., Peterman, B., Reichley, S.R., Lawrence, M. 2025. Systematic revision of the genus Orchidasma and description of Orchidasma orchilobata n. sp. from the loggerhead (Caretta caretta) and Kemp’s ridley turtle (Lepidochelys kempii). Systematic Parasitology. 102(44). https://doi.org/10.1007/s11230-025-10243-x.
DOI: https://doi.org/10.1007/s11230-025-10243-x

Interpretive Summary: Flukes are important parasites for numerous economically- and ecologically-important terrestrial and aquatic species. In US catfish aquaculture, the trematode (fluke) Bolbophorus damnificus is one of the primary parasites associated with industry losses; however, many other parasite species are found in catfish ponds and the animals that frequent them, making rapid and consistent identification crucial to mitigating parasite-borne diseases. Technological advances in computing power and genomic sequencing have provided new tools in the analysis of parasites, leading to restructuring of related species and greater understanding of disease. In this study, collaborating scientists from USDA-ARS and Mississippi State University used opportunistic sampling of stranded sea turtles to evaluate new morphological and molecular tools for describing new parasite species and garnering new ideas on methods for demonstrating complete life cycles. The results of the study used morphometry (body and organ dimensions) to define key characteristics which may be used to distinguish similar species. The manuscript also proposes the recognition of a new species of Orchidasma in sea turtles. The methods evaluated here provide the basis for additional studies of flukes and other parasites associated with disease in a range of natural and aquaculture settings, including US catfish.

Technical Abstract: Adult flukes of the genus Orchidasma were collected from the intestinal tracts of loggerhead Caretta caretta and Kemp’s ridley Lepidochelys kempii sea turtles as part of diagnostic investigations into sea turtle strandings. Two morphologically distinct species were present: one represented the type-species Orchidasma amphiorchis and an undescribed species. Orchidasma amphiorchis is redescribed and Orchidasma orchilobata n. sp. is described based on morphological, molecular, and phylogenetic analyses. Oxford Nanopore Technology and Illumina sequencing were used to generate complete mitochondrial genomes and nuclear ribosomal operons for both species. Sanger sequencing from additional hologenophore specimens for both species were used to assess interspecific and intraspecific variability. Single locus phylogenetic analyses of aligned 28S rDNA sequences and concatenation of mitochondrial genes of the two species and other trematodes were performed to assess taxonomic affinity of Orchidasma. Analysis of 28S rDNA sequences placed O. amphiorchis and O. orchilobata n. sp. as members of the Monorchioidea and closest to Skrjabinopsolus nudidorsalis, a member of Deropristidae. This disagreed with previous inclusion of Orchidasma as a member of Telorchiidae within Plagiorchioidea. Whole mitochondrial genome sequencing and phylogenetic analysis resulted in similar topology, suggesting a revision to include Orchidasma as a member of Deropristidae supported by shared morphological characters and nucleotide sequence data with deropristiid congeners.