Anisakid biodiversity in the pygmy sperm whale ( Kogia breviceps ) stranded along the Spanish Atlantic coast

Anisakid nematodes are widespread parasites of marine mammals, characterized by complex life cycles involving invertebrate and fish hosts. While these parasites generally exhibit low specificity for intermediate hosts, they often show distinct associations with definitive hosts, suggesting a long evolutionary history between parasites and marine mammals. However, anisakid biodiversity in kogiid whales remains poorly understood. Adult Skrjabinisakis brevispiculata, S. paggiae, S. physeteris, Pseudoterranova ceticola and P. kogiae have been reported from Kogia breviceps and K. sima . This study investigated anisakid biodiversity in 9 pygmy sperm whales ( Kogia breviceps ) stranded along the Galician coast (NW Spain). A total of 500 nematodes randomly selected from the whales’ stomachs were morphologically assigned to morphotypes. Of these, 250 specimens were further characterized using sequences of the mitochondrial cox2 gene, the ITS rDNA region and the 28S rDNA gene. Skrjabinisakis brevispiculata, S. paggiae, Pseudoterranova ceticola, Anisakis simplex (s.s.) and A. pegreffii were identified. Molecular analyses further revealed that S. paggiae may represent a complex of closely related cryptic taxa. In addition, 2 Pseudoterranova genotypes were detected in syntopy within a single host: P. ceticola and a second taxon likely corresponding to P. kogiae , based on its genetic affinity with adult specimens previously reported from Australian waters. These findings reveal a greater diversity of anisakid nematodes in the pygmy sperm whale than previously recognized. K. breviceps appears to host a distinctive assemblage of anisakid parasites and likely represents an important definitive host contributing to the maintenance of anisakid biodiversity in mesopelagic and deep-sea food webs.