DESCRIPTIONS OF NEORHADINORHYNCHUS NUDUM (CAVISOMIDAE) AND HETEROSENTIS PARAHOLOSPINUS N. SP (ARHYTHMACANTHIDAE) (ACANTHOCEPHALA) FROM FISH ALONG THE PACIFIC COAST OF VIETNAM, WITH NOTES ON BIOGEOGRAPHY

Two species of acanthocephalans are described from fishes caught along the Pacific coast off eastern Vietnam in 2016: (1) Neorhadinorhynchus nudum (Harada, 1938) Yamaguti, 1939 (Cavisomidae) from the frigate tuna Auxis thazard (Lacepede) (Scombridae) in Nha Trang, Pacific south Vietnam, and (2) Heterosentis paraholospinus n. sp. (Arhythmacanthidae) from 3 species of fish: the common ponyfish Leiognathus equulus (Forsskal) (Leiognathidae) and the torpedo scad Megalaspis cordyla (Linn.) (Carangidae) off Nha Trang and Binh Thuan, respectively, and the yellowspotted ponyfish Nuchequula flavaxilla Kimura, Kimura, and Ikejima (Leiognathidae) at Quang Ninh in Pacific waters of Vietnam. Females of N. nudum are fully described for the first time in the Pacific Ocean. Heterosentis paraholospinus n. sp. is similar to Heterosentis holospinus Amin, Heckmann, and Ha, 2011, in having an unspined anterior trunk cone, nucleated pouch at the posterior end of the receptacle, and spines covering the entire trunk, but it differs in having a long cylindrical trunk, lemnisci much longer than the receptacle, more and different-sized proboscis hooks, and subterminal female gonopore. Biogeographical notes are discussed for both genera.