Corononema vulgare sp. n. and Hofmaenneria coralis sp. n. (Nematoda, Monhysterida) from coral reefs off the coast of Vietnam.

Two new nematode species of the order Monhysterida, found in coral reefs on the coast of Vietnam, are described and illustrated. Corononema vulgare sp. n. morphology is similar to C. thai Nicholas & Stewart, 1995 but differs from it by the shorter outer labial setae, shorter tail in males, and a different shape of the guiding lateral bodies in the spicular apparatus of males. Hofmaenneria coralis sp. n. morphology is close to H. niddensis Gerlach & Meyl, 1957 and H. optata Alekseev, 1983. The new species differs from the first species by having thinner body, a shorter and less slender tail, and shorter spicules. The new species differs from H. optata in having a longer body, shorter pharynx, shorter tail, and longer outer labial setae.

Description of three new Sphaerolaimus species (Nematoda: Sphaerolaimidae) form the South China Sea.

The family Sphaerolaimidae Filipjev, 1918 combines nematodes characterized by finely striated cuticle, round amphids, broad buccal cavity with longitudinal ribs, and females with one anterior ovary. Sphaerolaimus Bastian, 1865 species from this family are found in intertidal and subtidal sediments and have also been reported from mangroves and estuary. Three new species of Sphaerolaimus were found and described from the South China Sea. Sphaerolaimus callisto sp. nov. is characterized by the relatively long body, small amphids and long spicules. Sphaerolaimus callisto sp. nov. is similar to S. cuneatus Paramonov, 1929, but differs by the longer body (2350-2690 µm vs 1980-1990 µm), index b (5.1-5.6 vs 3.9-4.1), absence of precolacal supplements, and longer spicules (321-356 µm vs 270 µm). Sphaerolaimus ganymede sp. nov. is characterized by large amphids and the presence of sexual dimorphism in amphid size. Sphaerolaimus ganymede sp. nov. is close to Sphaerolaimus maeoticus Filipjev, 1922, but differs by the presence of lateral alae, indexes a (12.3-17.5 vs 20-27) and c (7.9 vs 9-10), bigger amphids in male (14.6-15.7 µm vs 11 µm). Sphaerolaimus io sp. nov. is characterized by small amphids and short apophyses of gubernaculum. Sphaerolaimus io sp. nov. is similar to Sphaerolaimus pacificus Allgen, 1947, but differs by bigger size (1480-1525 µm vs 1140 µm), presence of lateral alae, and index c (7.5-8 µm vs 14.3 µm). After critical evaluation of the genus we recognize 35 valid species and provide dichotomous and pictorial keys to species.

Paranticoma lepta sp. n. and Elzalia bipectinella Hope amp; Aryuthaka, 2009 from water bodies of Vietnam.

Two nematode species found in water bodies of Vietnam are described and illustrated. Paranticoma lepta sp. n., found in mangroves of the Yen River estuary is morphologically close to P. bendaense Micoletzky, 1930 and P. tricerviseta Zhang, 2005. From the former species it differs by the shorter cephalic setae and shorter tail, more anteriorly located cervical setae and shorter spicules. From the second species it differs by its thicker body, comparatively longer tail, longer spicules and absence of tooth-like structures in stoma. An illustrated description of males and females of Elzalia bipectinella Hope Aryuthaka 2009 is given, originally described from mangrove forest in the Andaman Sea coastal zone of east Thailand. Females of this species are described for the first time.

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.

Paracomesoma minor sp. n. and Microlaimus validus sp. n. (Nematoda) from the coast of Vietnam.

Two nematode species isolated from sediments of the littoral zone of South China Sea on the coast of Vietnam are described and illustrated. Paracomesoma minor sp. n. is closely related to P. elegans Gagarin & Thanh, 2009 and P. lissum Gagarin & Thanh, 2009. It differs from the former species in the shorter body, longer and more slender tail, longer cephalic setae and shorter spicules, and from the latter species in the shorter body, longer cephalic setae, presence of cervical setae and smaller number of precloacal supplements in males. Microlaimus validus sp. n. is morphologically closest to M. citrus Gerlach, 1959 and M. nanus Blome, 1982 and differs from both species in the longer body, relatively shorter pharynx and relatively shorter and thicker tail. 

A review of the genus Litinium Cobb, 1920 (Nematoda: Enoplida: Oxystominidae) with descriptions of four new species from two contrasting habitats.

Four new species of the genus Litinium are described from mangroves and from deep sea. The genus Litinium now includes ten valid species. An emended generic diagnosis and a pictorial guide for species identification are given. Litinium quangi sp. n. and L. curticauda sp. n., both found in mangroves of South Vietnam, are morphologically similar and differ from other congeneric species in body size, having short anterior setae, ovoid amphideal fovea and a short rounded tail. Litinium quangi differs from L. curticauda in the number of midventral preanal supplementary setae (one in L. quangi and two in L. curticauda) and relative tail length (c' 1.12-1.63 in L. quangi and 0.83-0.94 in L. curticauda). Litinium abyssorum sp. n. and L. profundorum sp. n., both collected from the Angola Basin, South-East Atlantic Ocean, at depth 5400 m, are also morphologically similar and differ from other species of the genus by having a smaller body and relatively large amphideal fovea with deep invagination of the anterior edge. Litinium abyssorum differs from L. profundorum in the number of midventral preanal setae (two in L. abyssorum, one in L. profundorum), relative tail length (c' 3.61 in L. abyssorum and 1.17 in L. profundorum) and L. abyssorum has unequal spicules.