Rhadinorhynchus oligospinosus n. sp. (Acanthocephala, Rhadinorhynchidae) from mackerels in the Pacific Ocean off Peru and related rhadinorhynchids in the Pacific, with notes on metal analysis.

Specimens of a new species of Rhadinorhynchus Lühe, 1911 are described from the chub mackerel Scomber japonicus (Scombridae) and the Chilean Jack mackerel Trachurus murphyi (Carangidae) (possibly a subspecies of Trachurus symmetricus) from the Pacific Ocean off the Peruvian coast at the Port of Chicama, La Libertad. Specimens of Rhadinorhynchus oligospinosus n. sp. are somewhat small having 11-14 rows of alternating proboscis hooks with 20-22 hooks each with posteriormost hooks in a continuous ring. Ventral hooks are robust with prominent roots but dorsal hooks are slender and shorter with discoid roots. Trunk spines are in two zones separated by a non-spiny region. Anterior trunk spines are in 2-3 complete circles but posterior spines are only ventral and lateral, and do not extend posterior to the level of the posterior end of the proboscis receptacle in both sexes. The new species is closest to Rhadinorhynchus seriolae (Yamaguti, 1963) Golvan, 1969 found in Japanese and Australian waters, but not as close to 19 other species found in the same Pacific waters off Australia, Japan, and Vietnam. In R. seriolae, posterior trunk spines extend well past the receptacle in females, among other diagnostic differences. Proboscis hooks of the new species were analyzed for chemical elements using X-ray in conjunction with EDAX (energy-dispersive analysis for X-ray) software; sulfur had a higher concentration at the edge than the middle of cut hooks.