Description of Three New Species of Rhadinorhynchus Lühe, 1911 (Acanthocephala: Rhadinorhynchidae) from Marine Fish off the Pacific Coast of Vietnam.

BACKGROUND: Of the 43 valid species of Rhadinorhynchus Lühe, 1911, 20 species are now known from the Pacific Ocean off Australia, Japan, and Vietnam. We have already described over 50 species and higher taxa from the Pacific Ocean off Vietnam over the last 15 years. PURPOSE: The present research is a continuation of our efforts to taxonomically map new acanthocephalan taxa, especially from Vietnam. Some of our collections in 2016 and 2017 revealed the presence of new species of the genus Rhadinorhynchus from various species of marine fish off the Pacific coast of Vietnam. We provide descriptions of these new species here. METHODS: Standard methods of collection and examination of marine hosts, processing and illustrating of specimens, and taxonomic identification of parasites using the extensive collections of the lead author were used. Type specimens were deposited at the Harold W. Manter Lab. collection, Lincoln, Nebraska. RESULTS: Three species Rhadinorhynchus are described from marine fish off the Vietnamese coast. Rhadinorhynchus circumspinus n. sp. with fusiform trunk, 1 field of anterior trunk spines, and anteriorly globular proboscis with up to 21 dorsoventrally differentiated hooks in 17-18 rows is described from Triacanthus biaculeatus Bloch (Triacanthidae) off Hai Phong. Rhadinorhynchus pacificus n. sp. with cylidrical trunk and proboscis with up to 25 dorso-ventrally similar hooks in 14-18 rows and trunk spines in 2 fields of dorsal, ventral and lateral spines is described from Auxis thazard (Lacepède) and Auxis rochei (Lacepède) (Scombridae) off Nha Trang. Rhadinorhynchus multispinosus n. sp. with cylindrical trunk and proboscis with up to 32 dorso-ventrally differentiated hooks in 12 rows, and many trunk spines in 2 fields of dorsal, ventral and lateral spines is described from Decapterus maruadsi (Temminck and Schlegel) (Carangidae) also off Hai Phong. Rhadinorhynchus polynemi Smales, 2014 of Australia is not the Indian species (with smallest basal hooks) as the basal hooks are largest and is now named Rhadinorhynchus australis nom. nov. (=Rhadinorhynchus polynemi Smales, 2014). Rhadinorhynchus trivandricus George and Nadakal, 1978 with smallest basal hooks and 8 pyriform cement glands is relegated to genus Indorhynchus Golvan, 1969. CONCLUSIONS: With the description of these 3 new species, the numner of valid species of Rhadinorhynchus has now increased to 46. We include a new generic diagnosis to accommodate the increased knowledge of variability within this genus.

Redescription and molecular analysis of Neoechinorhynchus (Neoechinorhynchus) johnii Yamaguti, 1939 (Acanthocephala, Neoechinorhynchidae) from the Pacific Ocean off Vietnam.

Neoechinorhynchus (Neoechinorhynchus) johnii Yamaguti, 1939 is redescribed from Eleutheronema tetradactylum (Polynemidae), Johnius carouna (Sciaenidae), Johnius sp., and Otolithes ruber (Sciaenidae) along the north and south coasts of Vietnam. Our description completes missing and inadequate information in the original descriptions and line drawings from Johnius goma in Japan and from Pseudosciaena diacanthus in the Indian Ocean. We add new information documented by scanning electron microscopy (SEM) and photomicroscopy, and explore the wide morphological diversity attributed to host species. The redescription includes: worms cylindrical with round proboscis with prominent apical organ, and large anterior hooks distant from small middle and posterior hooks; neck longer than the proboscis, nucleated lemnisci subequal, and receptacle with large basal triangulate cephalic ganglion and attached para-receptacle structure (PRS); male reproductive system in posterior half of trunk; adult females with introvert genital vestibule; and eggs spherical or rectangular. Gallium cuts and X-ray scans of hooks show high concentrations of sulfur on edge layer aiding in forming hardened calcium phosphate apatite of that layer with calcium and phosphorus in higher concentration in central part of hook. Molecular results consistently yielded a strongly supported distinct clade for the Neoechinorhynchus species from Vietnam for both 18S gene and the ITS1-5.8S-ITS2 region of ribosomal RNA. Phylogenetic analysis demonstrated that N. johnii occupies a separate position in the trees, probably indicating an Asian origin of this species.

The Morphological and Molecular Description of Acanthogyrus (Acanthosentis) fusiformis n. sp. (Acanthocephala: Quadrigyridae) from the Catfish Arius sp. (Ariidae) in the Pacific Ocean off Vietnam, with Notes on Zoogeography.

BACKGROUND: Most (82%) of the 46 recognized species of Acanthogyrus (Acanthosentis) Verma and Datta, 1929 are known from Asian freshwater fishes. Only three species of Acanthosentis are known from marine or brackish water fishes from India and Pakistan. We have discovered another marine species of Acanthosentis in the Pacific Ocean, off Vietnam. PURPOSE: The purpose is to describe the new species morphologically and molecularly and provide new information of its evolutionally relationships with other species of the subgenus. METHODS: Standard methods of collection and examination of marine hosts, processing and illustrating of specimens, and taxonomic identification of parasites using the extensive collection of the lead author were used. Specimens were further studied using energy-dispersive X-ray analysis and ion sectioning of hooks, SEM analysis, and molecular sequencing. Type specimens were deposited at the Harold W. Manter Lab. collection, Lincoln, Nebraska. RESULTS: Acanthogyrus (Acanthosentis) fusiformis n. sp. is described from the catfish, Arius sp. (Ariidae: Siluriformes) off the Pacific Coast of Vietnam at Bac Lieu in the Gulf of Thailand. The three other marine Indian species include A. (A.) arii Bilqees, 1971 which is also described from a similar catfish, Arius serratus Day off the Karachi coast in the Arabian Sea, Indian Ocean. Our new species from Vietnam is distinguished from the other 46 species by a combination of characters including a small fusiform trunk, complete circles of small hollow spines covering the entire trunk, prominent double apical organs often extending posteriorly past posterior hooks, middle and posterior hooks of equal size slightly smaller than anterior hooks, large neck continuous with the outline of the proboscis without distinct separation, big drop-shaped cephalic ganglion, extension of the proboscis receptacle anteriorly past the base of the proboscis up to the insertion point of the posterior hooks, presence of two para-receptacle structures (PRSs), free unattached thick lemnisci, short female reproductive system with filamentous attachment of the distal end of the uterine bell to the ventral body wall, and small narrowly ellipsoid eggs with thickened polar ends. Partial sequences of the 18S and internal transcribed spacers (ITS1-5.8S-ITS2) of ribosomal RNA were generated and used for phylogenetic analyses to confirm the taxonomic identity of Acanthogyrus (Acanthosentis) fusiformis n. sp. CONCLUSIONS: We describe unique morphological features of A. fusiformis never before known in the subgenus Acanthosentis. The uniqueness of A. fusiformis is further demonstrated by its EDXA fingerprint characterized by high levels of calcium and phosphorous in hooks. The zoogeography of species of Acanthosentis is elucidated in the Indian subcontinent, the Caribbean, China, and Africa. Molecular data have been available only in few species of Acanthogyrus (Acanthosentis) to date on GenBank database. For 18S, only two sequences from unknown Acanthosentis sp. from India are available, while for the ITS1-5.8S-ITS2 region, only sequences of A. cheni from China and of two unidentified species from Malaysia are available. Additional studies of species of Acanthosentis based on morphological and molecular genetic data will be needed to reconstruct the evolutionary history and phylogenetic affinities of this group of acanthocephalans.