New host and distribution records of Cosmocephalus obvelatus (Creplin, 1825) (Nematoda : Acuariidae), with morphometric comparisons

This is the first record of Cosmocephalus obvelatus (Creplin, 1825) Seurat, 1919 (Nematoda: Acuariidae), from Argentina (Valdes Peninsula, province of Chubut) and from the Magellanic penguin Spheniscus magellanicus (Aves: Sph eniscidae). The prevalence of this parasite was 31.3% and the mean intensit y was 5.4. Despite the wide geographic distribution and the great variety o f hosts parasitized by C. obvelatus (14 families belonging to 8 orders), th ere were no significant differences in morphological characteristics and me asurements from previous records. Both the wide distribution and the morpho metrical stability of C obvelatus may be explained by its ecology and mode of transmission.