Morphological and ultrastructural description of Nematopsis spisula sp. nov. (Apicomplexa) inhabiting Spisula solida (Bivalvia) on the Portuguese Atlantic coast

The present study describes the morphology and ultrastructure of the oocysts of a new species of the genus Nematopsis infecting different organs of the surf clam Spisula solida (Linnaeus, 1758) (Mollusca, Bivalvia) on the Portuguese Atlantic coast. Each oocyst (14.3 ± 0.2 µm long, and 10.3 ± 0.3 µm wide) contains a single uninucleate vermiform sporozoite. Single and grouped oocysts enveloped by a parasitophorous vacuole occur enclosed within host phagocytes externally, surrounded by a complex reticular ring-like structure formed by juxtaposed and parallel cysterns containing numerous small electron dense masses regularly distributed in their lumen. More advanced stages of infection show phagocytic degradation characterized by cytoplasmic vacuolarization and rupture of the parasitophorous vacuole membrane. Morphological and ultrastructural observations combined with host reaction specificity supports the erection of a new species, namely Nematopsis spisula sp. nov.