Revision of Johnston, 1937 (Acanthocephala: Polymorphidae) from a North American population using novel SEM images, Energy Dispersive X-ray Analysis, and molecular analysis.

We describe a population of the acanthocephalan Johnston, 1937 (Polymorphidae) from a California sea lion (Lesson, 1828) in California using novel scanning electron microscopy (SEM) images, Energy Dispersive x-ray analysis (EDXA), and molecular analysis for the first time. The taxonomic history of is replete with accounts using only line drawings some of which proved erroneous. The distribution of ventral spines on the female trunk has been the primary distinction between and Lincicome, 1943, its junior synonym; being continuous in the latter but discontinuous posteriorly in the former species. The distribution of ventral spines is invariably discontinuous in males. Our redescription and SEM images help to resolve this issue further validating the synonymy. Morphological variability has been documented between our California population and others from various host species in California, South Australia, South Shetlands, and the Argentinian coast. Our SEM images document features not previously detectable in line drawings, erroneously reported or missed in previous accounts. The EDXA spectra show high levels of calcium and phosphorous and low levels of sulfur characteristic of EDXA for other species of Lühe, 1904 provide support for the diagnostic distinction of . EDXA spectra were shown to be species specific and have diagnostic value in the taxonomy of the Acanthocephala. Our molecular analysis used amplification of 18S of ribosomal DNA and cytochrome c oxidase 1 (Cox1) gene. Phylogenetic analyses for Cox1 gene revealed a close relationship between Zdzitowiecki, 1984 and The phylogenetic trees confirmed that the isolates belonged to . The haplotype network inferred by Cox1 with sequences revealed that haplotypes clearly separated from each other and formed clusters related to samples from the Northern Hemisphere (the USA and Mexico), and the second from the Southern Hemisphere (Argentina, Brazil and Peru).