Occurrence of a New Apicomplexan Intracellular Parasite in the Digestive Gland of Bulla striata (Gastropoda: Cephalaspidea) from the South Coast of Portugal

A new intracellular parasite of the phylum Apicomplexa is described infecting the digestive gland of the gastropod Bulla striata from the south coast of Portugal. Only merogonial stages enclosed within parasitophorous vacuoles were observed by light and electron microscopy. The meront cytoplasm contained lipid droplets, rough endoplasmic reticulum cisternae, and several round or oval electron-dense microbodies closely associated with amylopectin granules, suggesting that these microbodies may represent glycosomes. Mitochondria or related organelles were not identified. A reticulum of branched tubules extending from the parasitophorous vacuole membrane was observed, likely increasing the surface available for metabolite exchange between parasite and host cell. Merozoites resulting from meront division were present within the parasitophorous vacuoles. They were elongated and slightly curved, measuring 7–8 µm in length and about 2 µm in width, and possessed an apical complex comprising numerous rod-shaped micronemes, rhoptries, and a conoid. Phylogenetic analyses based on a partial 18S rDNA sequence placed this parasite within the coccidian lineage, at the base of the ichthyocolid clade, a recently recognized group of apicomplexans previously known from fish blood cells. This finding expands the host range of ichthyocolids to gastropods and provides the first ultrastructural observations of this lineage, although only of merogonic stages.