Line drawings of specimens of Rhadinorhynchus oligospinosus from the mackerels Scomber japonicus and Trachurus murphyi from off the Pacific coast of Peru. Normal body wall thickness (A, B) not shown. (A) Holotype male. Note the lemniscus being shorter than the receptacle, the restricted distribution of posterior trunk spines, and posterior position of the reproductive system. The common sperm duct is lateral and ventral to the four cement glands. (B) Allotype female with the same distribution of lemniscus and posterior trunk spines as in the male. Measurement scale is the same as the male (A). (C) Detail of the long female reproductive system of specimens in (B); note the simple uterine bell and glands. (D) Apical, middle, posteriormost, and basal dorsal proboscis hooks in a male specimen. (E) Apical, middle, posteriormost, and basal ventral proboscis hooks in the same male specimen. Note the dorso-ventral diversification of hooks and the reduced dorsal hook roots. (F) A profile of a ventral anterior trunk spine in a female specimen. (G) A profile of a ventral posterior trunk spine in the same female specimen. (H) A ripe egg.