Adult specimens of Corynosoma australe Johnston, 1937 were recorded from the intestines of California sea lions, Zalophus californianus (Lesson), from Baja California Peninsula, Mexico, whereas larval forms were collected from two fish species on the Argentinian coast. Adult specimens of C. australe were morphologically characterized by having a cylindrical proboscis with 18-20 rows of 12-14 hooks per row and a cylindrical trunk expanded anteriorly into a disk with tiny, triangular spines spreading almost to three quarters of the hind-trunk in males and to the posterior body end in females. The aim of this study was to explore the genetic diversity and systematic position of C. australe distributed in the Americas. Newly generated sequences of the mitochondrial cytochrome c oxidase subunit 1 (cox 1) gene were compared with sequences available from GenBank. Phylogenetic analyses performed with the cox 1 dataset using maximum likelihood and Bayesian inference showed that the 11 new sequences of C. australe recovered from the California sea lion in northern Mexico plus the six sequences from Argentinian seashores formed a clade with other sequences of specimens previously identified as C. australe. The intraspecific genetic divergence among the isolates was very low, ranging from 1 to 1.7%, and in combination with the phylogenetic trees confirmed that the isolates belonged to the same species. The cox 1 haplotype network inferred with 27 sequences revealed 18 haplotypes divided into two clusters clearly separated from each other by 5 substitutions. The first cluster corresponded to specimens from the Northern Hemisphere (United States of America and Mexico), and the second corresponded to specimens from the Southern Hemisphere (Argentina and Brazil). The current evidence suggests that C. australe has an amphitemperate distribution and is associated mainly with otariids with secondary and independent colonization events to other mammals and the Magellanic penguin in the Southern Hemisphere.

Centro de Investigación en Alimentación y Desarrollo Sánchez Taboada Carret al Varadero Nacional km 6 6 Col Las Playitas Guaymas Sector Varadero Las Playitas 85480 Heroica Guaymas Sonora Mexico

Departamento de Zoología Instituto de Biología Universidad Nacional Autónoma de México Avenida Universidad 3000 Ciudad Universitaria 04510 Mexico City Mexico

Institute of Parasitology Biology Centre of the Czech Academy of Sciences Branišovská 31 37005 České Budějovice Czech Republic

Laboratorio de Mamíferos Marinos Centro para el Estudio de Sistemas Marinos Blvd Brown 2915 9120 Puerto Madryn Chubut Argentina; Universidad Nacional de la Patagonia San Juan Bosco UNPSJB Sede Puerto Madryn Blvd Brown 3000 9120 Puerto Madryn Chubut Argentina

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