The nematode community distribution in two estuaries of the Me Kong delta: Cung Hau and Ham Luong, South Vietnam

The highest numbers of nematodes with a percentage ranging from 76.4% in Cung Hau to 77% in Ham Luong estuaries. There were 92 genera (71 genera in Ham Luong and 62 genera in Cung Hau) of nematodes recorded in both estuaries. The mean nematode densities varied between 90 ± 31 - 1524 ± 269 ind.10 cm² and 105 ± 79 - 1120 ± 534 ind.10 cm² in Ham Luong and Cung Hau estuary, respectively. The nematode communities were mainly composed of Dichromadora, Daptonema, Oncholaimellus, Syringolaimus, Tripyloides, Parodontophora, Theristus and Halalaimus belonging to several dominant families, such as, Oncholaimidae, Xyalidae, Chromadoridae, Oxystominidae, Axonolaimidae and Sphaerolaimidae. In both estuaries, nematode density decreased from inland towards the mouth before they increased again at the mouth stations

New genus Asymmelaimus gen. n., sp n. and new marine nematode species of the subfamily Dorylaimopsinae de Coninck, 1965 (Comesomatidae Filipjev, 1918) from Halong Bay, Vietnam

One new genus and one new species are described from Halong Bay, Vietnam: Asymmelaimus vietnamicus gen. n., sp. n. and Dorylaimopsis halongensis sp. n. Asymmelaimus vietnamicus gen. n., sp. n. is characterized by an asymmetrical head with the anterior part of the buccal cavity leaning to the dorsal side and a narrow posterior part with weakly cuticularized walls and one dorsal and two ventrosublateral small teeth situated at the base of the anterior part, and a cuticular ornamentation consisting of one or two longitudinal rows of dots. Dorylaimopsis halongensis sp. it. is characterized by the head set off from the body by constriction, massive spicules with a 'velum' and a long tail (11.3 to 13.6 anal body diameters)

Six new species of the genus Onyx Cobb, 1891 (Nematoda: Desmodoridae) from coastal areas in Vietnam

Six new species of the genus Onyx are described from different coastal zones in Vietnam based on samples collected between 2004 and 2010. Onyx cangionensis sp. n. is characterised by the fact that males have 14-16 equal-sized and equal-distantly arranged sigmoidal precloacal tubular shaped supplements. Onyx blomei sp. n. is characterised by sexual dimorphism in the shape of the amphidial fovea. The male has an atypical amphid with posterior part spiral shaped with 2.5 turns and anterior part hook shaped, whereas the amphidial fovea in the female is simply multispiral with 2.25 turns. Onyx orientalis sp. n. is characterised by its very long cephalic setae and the presence of 18 light-refractive, slightly S-shaped, precloacal tubular supplements in the males. Onyx cobbi sp. n. is also characterised by its sexual dimorphism in the shape of the amphidial fovea: an elongated loop in the male and a multispiral in the female. There are 15 slightly S-shaped, precloacal supplements. The anterior supplement is half the size of the others. Onyx paradimorphus sp. n. is characterised by a multispiral amphidial fovea, spicules regularly bent, strongly cuticularised, 15 S-shaped supplements and 5 papillae with setae within the spicules region. Onyx mangrovi sp. n. is characterised by 17-23 supplements with a complex structure: anterior part is sigmoidal-shaped, posterior part is hook-shaped and by its very short tail with dorsally curved tip

Bernardius lineatus gen. n., sp. n. (Enoplida: Enchelidiidae), a remarkable nematode with ornamented cuticle from a Brazilian tropical sandy beach

Bernardius lineatus gen. n., sp. n. is described from a sandy beach at Tamandaré Bay, Brazil. It possesses the main characteristics of the family Enchelidiidae (Nematoda: Enoplida), but is unique by the presence of a body cuticle ornamented with longitudinal ridges formed by small rods, an entirely different character to all other members of the order Enoplida. The new genus is also characterised by a long, subdivided, buccal cavity with two subventral teeth and numerous denticles and the arrangement of the anterior sensilla in two crowns, the anterior crown being papilliform and the posterior crown consisting of six external labial and four cephalic sensilla, setiform. The relationships of the genera within the Enchelidiidae are discussed and an emended family diagnosis provided

Chromaspirina guanabarensis sp.n. (Nematoda: Desmodoridae) and a new illustrated dichotomous key to Chromaspirina species

A new species of Chromaspirina is described from Bica Beach, a polluted beach situated at Ilha do Governador, Guanabara Bay on the coast of Rio de Janeiro (Brazil). The new species belongs to the group of species within the genus which bears a poorly developed dorsal tooth. The new species is characterized by large body size, conoid tail shape, small acute dorsal tooth, long slender spicules with sclerotised hooked capitulum, and sexual dimorphism of the non-striated part of the tail. A new illustrated dichotomous key to males of species of Chromaspirina is proposed

Intertidal nematode communities in the Mekong estuaries of Vietnam and their potential for biomonitoring

Nematode communities in eight Mekong estuaries were investigated during the dry season. The aim of the study was to identify the structure and the diversity of the communities in relation to the main environmental characteristics. In each estuary, three to four intertidal sampling stations were identified at regular distances from the mouth to up to 45 km land inward. The nematode communities showed a strong correlation with sediment composition and to a lesser degree with chlorophyll a concentrations. Multivariate analysis resulted in the identification of four types of communities. We identified two types of Desmodora communities in the sandy mouth stations and two types of Parodontophora communities in the silty sand stations. One of the silt associated communities showed a preference for higher chlorophyll a concentrations, resulting in higher densities and higher diversity, mainly of monhysterid species. Because of the strong association between community structure and sediment composition, nematodes are a meaningful tool for monitoring changes in their environment. In case their community deviates from what is expected based on sediment, it may serve as an early warning for disturbance

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