Abstract
We describe and characterize a new Isospora species from the black-faced cuckoo-shrike (Coracina novaehollandiae) in Western Australia, using both morphological and molecular approaches. Microscopic analysis of a fecal sample revealed 20 ellipsoidal oocysts, which are subspheroidal to ovoid, measuring 40-43 × 39-41 μm (mean 41.4 × 39.6 μm) with a length/width (L/W) ratio of 1.0-1.1 (mean 1.04). The oocyst wall is bi-layered (~1.5 μm thick), with a smooth outer layer constituting approximately two thirds of the total thickness. A micropyle is present, characterized by a slight invagination of the inner layer (~6.0 μm wide), but no micropyle cap is observed. Both the oocyst residuum and polar granule are absent. Sporocysts (n = 20) are ellipsoidal, measuring 23-24 × 13-14 μm (mean 23.3 × 13.4 μm) with an L/W ratio of 1.7-1.8 (mean 1.74). A flattened to knob-like Stieda body (~1.5 × 3.0 μm) is present, while sub-Stieda and para-Stieda bodies are absent. The sporocyst residuum is composed of granules clustered by a membrane, forming an irregular shape (~12.0 × 8.0 μm). Sporozoites exhibit anterior and posterior refractile bodies and a nucleus. Molecular analyses of the 18S rRNA, 28S rRNA, and COI gene loci demonstrated that this species forms a distinct clade with Isospora serinuse in phylogenetic trees based on all three loci. It shares genetic similarities with I. serinuse of 98.8%, 93.7%, and 98.9% for the 18S rRNA, 28S rRNA, and COI loci, respectively. Phylogenetic analysis confirms that this new species is closely related to I. serinuse. Based on these findings, we propose this isolate as a new species, Isospora coracinae n. sp. This is the first coccidian species identified from the Campephagidae family in Australia.