The Apicomplexa are obligate unicellular parasites found in terrestrial and aquatic environments. Nematopsis are found infecting marine invertebrates in a life cycle involving mollusks and crustaceans. In the present study, mantle and muscle tissues from nerite gastropods were microscopically examined for Nematopsis using wet mounts and histology. Oocysts contained one single sporozoite surrounded by an ellipsoidal wall and were surrounded by a parasitophorous vacuole within a host phagocyte. Length and width of fresh oocysts were measured and compared between host species. DNA was extracted from infected tissue, and regions of the rRNA gene were amplified using novel primers. Nematopsis-infected tissues from scallops from Argentina and Scotland were used as controls. The sizes of oocysts observed in nerite hosts from Saint Kitts were not significantly different. DNA sequences of Nematopsis isolated from nerite hosts in this study were identical and phylogenetically related to sequences obtained from scallops. Bayesian and maximum likelihood phylogenetic analyses robustly place the Nematopsis DNA sequences from this study with Nematopsis from scallops in Florida and members of the family Porosporidae. We conclude that marine Nematopsis will group within this clade or within the Porosporidae. We have provided specific oligonucleotide primers to assist with the molecular study of the Porosporidae.
Keywords: Nematopsis; Cephaloidophoroidea; Porosporidae; gastropod; gregarine; nerite.
© 2025 The Author(s). Journal of Eukaryotic Microbiology published by Wiley Periodicals LLC on behalf of International Society of Protistologists.