Nguyen Dinh Tu

Meiobenthos in estuary part of ha long bay (gulf of tonkin, south china sea, vietnam)

The distribution of the taxonomical composition and the density of meiobenthos depending on some factors of environment has been studied in bottom sediments of the northern estuary part of Ha Long Bay (Cua Luc estuary). The basic factor of influence on meiobenthic community structure was the granulometric composition of sediment. The greatest taxonomic diversity is noted in the silted sands, lowest — in the silty sediments. The density of meiobenthic community was higher in the silty sediments. Slightly expressed correlation between the density of nematodes and the percentage of silty particles in the sediments is detected (Spearman rank correlation coefficient was 0.49±0.21, p=0.035). The nematodes were dominant at all stations. In total, representatives of 66 species of nematodes belonging to 17 families and 52 genera were identified.

Paracomesoma paralongispiculum sp. n.: a New species of nematode from mangroves of Can Gio (Vietnam) and taxonomy of the genus Paracomesoma Hope et Murphy, 1972 (Nematoda: Araeolaimida)

A literature review reveals that 13 species are described belonging to the genus Paracomesoma Hope and Murphy, 1972. In Can Gio mangrove forest, Ho Chi Minh city, Vietnam, one new species Paracomesoma paralongispiculum n. sp. was found, which brings the number of species up to 14. This species differs from all known species of this genus by its very long spicules (12 times a.b.d) and 11–12 papillae supplements all confined within the spicular region.

Two new species of free-living nematodes (Nematoda and Chromadorea) from mangrove thicket in Vietnam

Illustrated descriptions of two new species of free-living nematodes found in the dense mangrove thicket in river estuaries of Vietnam are given. Metachromadora (Metachromadoroides) orientalis sp. n. is morphologically similar to M. (M.) zaixsi Pastor de Ward, 2004, but it has longer and thicker tail, a more anterior position of the vulva, a different shape of amphidial foveae, a larger pharyngeal basal bulb, and longer spicules, and males have differently armed tails. Morphologically, Terschellingia lutosa sp. n. is closer to T. elegans Gagarin, Nguyen Vu Thanh, 2003 and T. supplementata Tchesunov, 1978 and differs from both of them by a less slender tail, a wider body at the area of head setae, and longer spicules. An identification key to the valid species of the genus Metachromadora (Metachromadoroides) is given.

Two new nematode species of the genus Daptonema Cobb, 1920 (Nematoda, Xyalidae) from mangrove forest estuary of the Red River (Vietnam)

Illustrated discriptions are given of two new marine free-living nematode species of the genus Daptonema Cobb, 1920, D. paraoxyuroides sp. n. and D. balatum sp. n., found in the estuary of the Red River in North Vietnam. D. paraoxyuroides sp. n. resembles D. oxyuroides, but differs from it in its shorter and thicker body, less slender tail, shorter cephalic setae, and shorter spicules. D. balatum sp. n. differs from all known valid species of the genus Daptonema by the special structure of the copulative apparatus of males.

Revision of the genus Parasphaerolaimus (Nematoda: Sphaerolaimidae) with description of new species

The family Sphaerolaimidae Filipjev, 1918 includes nematodes that are characterized by the finely striated cuticle, round amphids, broad buccal cavity with longitudinal ribs, and single anterior ovary in females. Parasphaerolaimus species from this family are found in intertidal and subtidal sediments and have also been reported from mangroves and estuaries. Parasphaerolaimus pilosus sp. n. is characterized by the moderately plump body, presence of lateral alae, long cervical setae, small amphids in males, and relatively short spicules. As a result of a comprehensive evaluation of species descriptions, eight species in the genus Parasphaerolaimus are recognized valid, and an identification key to species level is provided.

Free-living nematodes from mangrove forest in the Yên River estuary (Vietnam)

Fifty species of free-living nematodes have been found in the Yên River estuary (northern Vietnam), ten of which are newly described species. The dominant species are Valvaelaimoides macroamphida Gagarin, 2016; V. minor Gagarin, 2016; Micromicron cephalatum Cobb, 1920; and Sphaerotheristus nothus Gagarin, Nguyen Vu Thanh, 2008. A list of the nematodes species, an illustrated description of the new species Theristus consobrinus sp. n., the main morphometric parameters of 13 valid species of the species group flevensis of the genus Theristus, and a pictorial key for determining males of this species group are provided.

Bolbolaimus obesus sp. n. (Nematoda, Desmodorida) from Mangrove Thickets in the Tien Yen River Estuary, Vietnam

An illustrated description of the nematode Bolbolaimus obesus sp. n. from a mangrove forest of the Yen River estuary, Vietnam is given. Bolbolaimus obesus sp. n. is close to B. abebei Muthumbi et Vincx 1999 and B. bahari Muthumbi et Vincx 1999, but differs from both by the shorter body, strongly sclerotized body walls of the cheilostoma, a different position of the amphidial fovea, and longer gubernaculum.

Two new species of the genus Deontolaimus de Man, 1880 (Nematoda: Leptolaimidae) from mangrove ecosystems of Vietnam

Two new species of the free-living marine nematode genus Deontolaimus (Leptolaimidae) are described from mangrove forests of the Can Gio Biosphere Reserve and Tien Yen, Quang Ninh, Vietnam. D. mangrovi sp. nov. is distinguished from D. papillatus de Man, 1880 and D. cangioensis sp. nov. by tail shape: conical and then elongated, without pointed tip. Deontolaimus cangioensis sp. nov. resembles D. papillatus in body shape, especially in the pointed tail terminus. D. cangioensis differs from D. papillatus in having a complicated gubernaculum with dorsally curved apophyses.

Preliminary study on the parasitic helminth fauna on marine fishes in the coastal waters of Hai Phong province

Study on the parasitic worms in marine fishes has not been realized in Vietnam for long time. Only in 60th and 70th decades of the last 20th century, Russian parasitologists such as Parukhin, Oshmarin, Mamaev and Lebedev had investigated the helminth fauna of marine fishes in Gulf of Tonkin describing about 80 helminth species. During the January, February, April, July and October, 2008 the study on helminth and crustacean fauna parasiting on marine fishes has been realized in the coastal waters of Hai Phong province. In total, 44 fish species has studied for present seeking of the parasitic worms and crustaceans. Among all studied 44 fish species, 50.0% were infected by monogeneans; 65.9% were infected by trematodes; 15.9% were infected by cestodes; 56.8% were infected by nematodes; 18.2% were infected by acanthocephalans and only 13.7% were infected by parasitic crustaceans. 70 parasitic worms and crustaceans were recorded, belonging to Monogenea, Acanthocephala, Trematoda, Cestoda, Nematoda, Copepoda, Isopoda. Four parasitic crustacean species were found on 7 different marine fish species for the first time in Vietnam.