Inverted base composition skews and discontinuous mitochondrial genome architecture evolution in the Enoplea (Nematoda).

BACKGROUND: Within the class Enoplea, the earliest-branching lineages in the phylum Nematoda, the relatively highly conserved ancestral mitochondrial architecture of Trichinellida is in stark contrast to the rapidly evolving architecture of Dorylaimida and Mermithida. To better understand the evolution of mitogenomic architecture in this lineage, we sequenced the mitogenome of a fish parasite Pseudocapillaria tomentosa (Trichinellida: Capillariidae) and compared it to all available enoplean mitogenomes. RESULTS: P. tomentosa exhibited highly reduced noncoding regions (the largest was 98 bp), and a unique base composition among the Enoplea. We attributed the latter to the inverted GC skew (0.08) in comparison to the ancestral skew in Trichinellidae (-0.43 to -0.37). Capillariidae, Trichuridae and Longidoridae (Dorylaimida) generally exhibited low negative or low positive skews (-0.1 to 0.1), whereas Mermithidae exhibited fully inverted low skews (0 to 0.05). This is indicative of inversions in the strand replication order or otherwise disrupted replication mechanism in the lineages with reduced/inverted skews. Among the Trichinellida, Trichinellidae and Trichuridae have almost perfectly conserved architecture, whereas Capillariidae exhibit multiple rearrangements of tRNA genes. In contrast, Mermithidae (Mermithida) and Longidoridae (Dorylaimida) exhibit almost no similarity to the ancestral architecture. CONCLUSIONS: Longidoridae exhibited more rearranged mitogenomic architecture than the hypervariable Mermithidae. Similar to the Chromadorea, the evolution of mitochondrial architecture in enoplean nematodes exhibits a strong discontinuity: lineages possessing a mostly conserved architecture over tens of millions of years are interspersed with lineages exhibiting architectural hypervariability. As Longidoridae also have some of the smallest metazoan mitochondrial genomes, they contradict the prediction that compact mitogenomes should be structurally stable. Lineages exhibiting inverted skews appear to represent the intermediate phase between the Trichinellidae (ancestral) and fully derived skews in Chromadorean mitogenomes (GC skews = 0.18 to 0.64). Multiple lines of evidence (CAT-GTR analysis in our study, a majority of previous mitogenomic results, and skew disruption scenarios) support the Dorylaimia split into two sister-clades: Dorylaimida + Mermithida and Trichinellida. However, skew inversions produce strong base composition biases, which can hamper phylogenetic and other evolutionary studies, so enoplean mitogenomes have to be used with utmost care in evolutionary studies.

Profiling the Proteome of Cyst Nematode-Induced Syncytia on Tomato Roots.

Cyst nematodes are important herbivorous pests in agriculture that obtain nutrients through specialized root structures termed syncytia. Syncytium initiation, development, and functioning are a research focus because syncytia are the primary interface for molecular interactions between the host plant and parasite. The small size and complex development (over approximately two weeks) of syncytia hinder precise analyses, therefore most studies have analyzed the transcriptome of infested whole-root systems or syncytia-containing root segments. Here, we describe an effective procedure to microdissect syncytia induced by Globodera rostochiensis from tomato roots and to analyze the syncytial proteome using mass spectrometry. As little as 15 mm2 of 10-µm-thick sections dissected from 30 syncytia enabled the identification of 100-200 proteins in each sample, indicating that mass-spectrometric methods currently in use achieved acceptable sensitivity for proteome profiling of microscopic samples of plant tissues (approximately 100 µg). Among the identified proteins, 48 were specifically detected in syncytia and 7 in uninfected roots. The occurrence of approximately 50% of these proteins in syncytia was not correlated with transcript abundance estimated by quantitative reverse-transcription PCR analysis. The functional categories of these proteins confirmed that protein turnover, stress responses, and intracellular trafficking are important components of the proteome dynamics of developing syncytia.

Flatworm mucus as the base of a food web.

BACKGROUND: By altering their habitats, engineering species can improve their own fitness. However, the effect of this strategy on the fitness of coexisting species or on the structure of the respective food web is poorly understood. In this study, bacteria and bacterivorous nematodes with short (Caenorhabditis elegans) and long (Plectus acuminatus) life cycles were exposed to the mucus secreted by the freshwater flatworm Polycelis tenuis. The growth, reproduction, and feeding preferences of the nematodes in the presence/absence of the mucus were then determined. In addition, confocal laser scanning microscopy (CLSM) was used to examine the structural footprint of the mucus and the mucus colonization dynamics of bacteria and protozoans. RESULTS: Mucus exposure resulted in a greater reproductive output in P. acuminatus than in C. elegans. In a cafeteria experiment, both nematode species were attracted by bacteria-rich patches and were not deterred by mucus. CLSM showed that the flatworms spread a layer of polysaccharide-rich mucus ca. 15 µm thick from their tails. Subsequent colonization of the mucus by bacteria and protozoans resulted in an architecture that progressively resembled a complex biofilm. The presence of protozoans reduced nematode reproduction, presumably due to competition for their bacterial food supply. CONCLUSION: Animal secretions such as mucus may have broader, community-level consequences and contribute to fueling microbial food webs.

Medium-Chain Fatty Acids from Eugenia winzerlingii Leaves Causing Insect Settling Deterrent, Nematicidal, and Phytotoxic Effects.

Eugenia winzerlingii (Myrtaceae) is an endemic plant from the Yucatan peninsula. Its organic extracts and fractions from leaves have been tested on two phloem-feeding insects, Bemisia tabaci and Myzus persicae, on two plant parasitic nematodes, Meloidogyne incognita and Meloidogyne javanica, and phytotoxicity on Lolium perenne and Solanum lycopersicum. Results showed that both the hexane extract and the ethyl acetate extract, as well as the fractions, have strong antifeedant and nematicidal effects. Gas chromatography-mass spectrometry analyses of methylated active fractions revealed the presence of a mixture of fatty acids. Authentic standards of detected fatty acids and methyl and ethyl derivatives were tested on target organisms. The most active compounds were decanoic, undecanoic, and dodecanoic acids. Methyl and ethyl ester derivatives had lower effects in comparison with free fatty acids. Dose-response experiments showed that undecanoic acid was the most potent compound with EC50 values of 21 and 6 nmol/cm2 for M. persicae and B. tabaci, respectively, and 192 and 64 nmol for M. incognita and M. javanica, respectively. In a phytotoxicity assay, medium-chain fatty acids caused a decrease of 38-52% in root length and 50-60% in leaf length of L. perenne, but no effects were observed on S. lycopersicum. This study highlights the importance of the genus Eugenia as a source of bioactive metabolites for plant pest management.

Nematode parasites in young cattle: what role for unexpected species?

AIMS To investigate the timing of infection of beef calves with sheep nematode species on three sheep and beef farms, and to determine the prevalence of cross-infection in calves before weaning across a larger number of farms. METHODS Farms in the Far North, Gisborne and Tararua districts, in the North Island of New Zealand, were enrolled in 2014. Fresh faecal samples were collected from approximately 10 calves on each farm between birth and up to 5 months after weaning. In 2016, faecal samples were collected from calves before weaning from 22 farms across the upper North Island. For both trials faecal samples were assessed for faecal nematode egg counts and cultured to determine parasite genus. For samples from the three farms, larvae were identified to species using a multiplex PCR assay. RESULTS On the three farms, the median percentage of sheep nematode species detected in faecal cultures was 25 (min 3, max 77)%. The main sheep species detected were Cooperia curticei and Haemonchus spp. (putatively contortus). In faecal samples collected before weaning from 22 farms, Haemonchus spp. were present in 19/22 samples, and the median prevalence was 15 (min 0, max 73)% of the total larvae cultured. CONCLUSIONS AND CLINICAL RELEVANCE The implications of sheep nematode species being present in calves should be considered by farmers and veterinarians when undertaking anthelmintic efficacy testing, as they may contribute to false conclusions regarding anthelmintic efficacy. Pre-weaning calves may also be a possible source of contamination and/or refugia for Haemonchus spp. on farms and should be considered when developing parasite control plans for sheep.

Transgenesis by microparticle bombardment for live imaging of fluorescent proteins in Pristionchus pacificus germline and early embryos.

Pristionchus pacificus is a free-living nematode used as a model organism for evolutionary developmental and ecological biology. Although a transgenic technique to form complex arrays by microinjection has been established in P. pacificus, transgene expression from the array in the germline and early embryos tends to be silenced. Here, we established a method to integrate transgenes into the genome of P. pacificus using microparticle bombardment with hygromycin B selection. Additionally, we isolated a mutant exhibiting significantly lower autofluorescence in the germline and early embryos, facilitating visualization of transgene-derived fluorescent proteins for live imaging. Transgenic lines constructed using these tools successfully expressed GFP-tagged proteins in the germline and early embryos and enabled live imaging of chromosomes, microtubules, and centrosomes.

First report of a symbiotic relationship between Xenorhabdus griffiniae and an unknown Steinernema from South Africa.

Strain WS9, a mutualistic-associated bacterium, was isolated from an unknown entomopathogenic Steinernema nematode, collected from a litchi orchard in Friedenheim, Mpumalanga, South Africa. Based on phenotypic and phylogenetic data of the 16S rRNA, gltX, recA, dnaN, gyrB and infB gene sequences, strain WS9 is identified as X. griffiniae. Strain WS9 has antibacterial activity against Gram-positive and Gram-negative bacteria. This is the first report of an association between X. griffiniae and an unknown Steinernema species from South Africa.

The complete mitochondrial genome of parasitic nematode Camallanus cotti: extreme discontinuity in the rate of mitogenomic architecture evolution within the Chromadorea class.

BACKGROUND: Complete mitochondrial genomes are much better suited for the taxonomic identification and phylogenetic studies of nematodes than morphology or traditionally-used molecular markers, but they remain unavailable for the entire Camallanidae family (Chromadorea). As the only published mitogenome in the Camallanina suborder (Dracunculoidea superfamily) exhibited a unique gene order, the other objective of this research was to study the evolution of mitochondrial architecture in the Spirurida order. Thus, we sequenced the complete mitogenome of the Camallanus cotti fish parasite and conducted structural and phylogenomic comparative analyses with all available Spirurida mitogenomes. RESULTS: The mitogenome is exceptionally large (17,901 bp) among the Chromadorea and, with 46 (pseudo-) genes, exhibits a unique architecture among nematodes. Six protein-coding genes (PCGs) and six tRNAs are duplicated. An additional (seventh) tRNA (Trp) was probably duplicated by the remolding of tRNA-Ser2 (missing). Two pairs of these duplicated PCGs might be functional; three were incomplete and one contained stop codons. Apart from Ala and Asp, all other duplicated tRNAs are conserved and probably functional. Only 19 unique tRNAs were found. Phylogenomic analysis included Gnathostomatidae (Spirurina) in the Camallanina suborder. CONCLUSIONS: Within the Nematoda, comparable PCG duplications were observed only in the enoplean Mermithidae family, but those result from mitochondrial recombination, whereas characteristics of the studied mitogenome suggest that likely rearrangement mechanisms are either a series of duplications, transpositions and random loss events, or duplication, fragmentation and subsequent reassembly of the mitogenome. We put forward a hypothesis that the evolution of mitogenomic architecture is extremely discontinuous, and that once a long period of stasis in gene order and content has been punctuated by a rearrangement event, such a destabilised mitogenome is much more likely to undergo subsequent rearrangement events, resulting in an exponentially accelerated evolutionary rate of mitogenomic rearrangements. Implications of this model are particularly important for the application of gene order similarity as an additive source of phylogenetic information. Chromadorean nematodes, and particularly Camallanina clade (with C. cotti as an example of extremely accelerated rate of rearrangements), might be a good model to further study this discontinuity in the dynamics of mitogenomic evolution.

Larvicidal and Nematicidal Activities of 3-Acylbarbituric Acid Analogues against Asian Tiger Mosquito, Aedes albopictus, and Pine Wood Nematode, Bursaphelenchus xylophilus.

Widespread concern for the occurrence of resistant strains, along with the avoidance of the use of highly toxic insecticides and their wide environmental dispersal, highlights the need for the development of new and safer pest control agents. Natural products provide inspiration for new chemical entities with biological activities, and their analogues are good lead compounds for the development of new pest control agents. For this purpose, we evaluated the larvicidal and nematicidal activities of 48 3-acylbarbituric acid analogues against the Asian tiger mosquito, Aedes albopictus and the pine wood nematode, Bursaphelenchus xylophilus, organisms of increasing global concern. Among the 48 3-acylbarbituric acid analogues, four compounds-10, 14d, 14g and 19b-showed >90% larvicidal activity against Ae. albopictus at 10 µg/mL concentration, and one (compound 10) showed the strongest larvicidal activity against Ae. albopictus, with a LC50 value of 0.22 µg/mL. Only compound 18 showed strong nematicidal activity against pine wood nematode. Most active compounds possessed similar physicochemical properties; thus, actives typically had ClogP values of around 1.40-1.50 and rel-PSA values of 16-17% and these similar cheminformatic characteristics reflect their similar structure. This study indicates that active 3-acylbarbituric acids analogues have potential as lead compounds for developing novel mosquito control agents.

A Comparative Study of Four Methods for the Detection of Nematode Eggs and Large Protozoan Cysts in Mandrill Faecal Material.

Coproscopical methods like sedimentation and flotation techniques are widely used in the field for studying simian gastrointestinal parasites. Four parasites of known zoonotic potential were studied in a free-ranging, non-provisioned population of mandrills (Mandrillus sphinx): 2 nematodes (Necatoramericanus/Oesophagostomum sp. complex and Strongyloides sp.) and 2 protozoan species (Balantidium coli and Entamoeba coli). Different coproscopical techniques are available but they are rarely compared to evaluate their efficiency to retrieve parasites. In this study 4 different field-friendly methods were compared. A sedimentation method and 3 different McMaster methods (using sugar, salt, and zinc sulphate solutions) were performed on 47 faecal samples collected from different individuals of both sexes and all ages. First, we show that McMaster flotation methods are appropriate to detect and thus quantify large protozoan cysts. Second, zinc sulphate McMaster flotation allows the retrieval of a higher number of parasite taxa compared to the other 3 methods. This method further shows the highest probability to detect each of the studied parasite taxa. Altogether our results show that zinc sulphate McMaster flotation appears to be the best technique to use when studying nematodes and large protozoa.

Two new species of Promonhystera Wieser, 1956 (Nematoda: Monhysterida: Xyalidae) from the South China Sea.

Two new species of free-living marine nematodes from the littoral sediment of the South China Sea are described as Promonhystera papilla sp. nov. and Promonhystera fluctispicula sp. nov. Both new species are characterized by striated cuticle; circular amphideal fovea; anterior sensilla in two circles, inner labial sensilla setiform; funnel-shaped buccal cavity; elongated spicules and conico-cylindrical tail. P. papilla sp. nov. is different from all known species of the genus by longer body length (more than 2.1mm versus less than 1.5 mm in other species), longer spicules (sp/a.b.d. = 4.14.6 versus 2.7) and males with three papilliform precloacal supplements and one small postcloacal papilla (versus absence) and gubernaculum boot-shaped. P. fluctispicula sp. nov. is similar to P. tricuspidata Wieser, 1956 in having similar waved spicules but differs from the latter species by tail conico-cylindrical (versus conical) and simple plate-like gubernaculum without tooth (versus gubernaculum with four distal teeth).

Two new species of Xyalidae Chitwood, 1951 (Nematoda, Monhysterida) from Chinese Sea Area.

Two new nematode species of the family Xyalidae were found in the intertidal zone of the Chinese coast, and they are described here as Daptonema sinica sp. nov. and Metadesmolaimus bulbosus sp. nov. Daptonema sinica sp. nov. is characterised by a relatively large body with a broad funnel-shaped buccal cavity; relatively long cephalic setae; a circular amphidial fovea posterior to the buccal cavity; slender spicules bending into a hook shape in the posterior half; a small plate-like gubernaculum without apophysis; and a conico-cylindrical slender tail with terminal setae. Metadesmolaimus bulbosus sp. nov. can be identified by its large buccal cavity, long cervical setae, multiple bulb-like pharyngeal muscular swellings, conico-cylindrical tail narrowing abruptly immediately posterior to the cloaca, straight clavated spicules with a broad proximal end and hooked distal end, and gubernaculum absent. An updated dichotomous key to the species of Metadesmolaimus is given.

Two new species of Sabatieria de Rouville, 1903 (Nematoda: Araeolaimida: Comesomatidae) from the Southern Ocean.

Two new free-living marine nematode species of the genus Sabatieria de Rouville, 1903 are described from the Southern Ocean using morphological and molecular data. Sabatieria brevicaudata sp. nov. is characterized by body length 14761740 m, short cephalic setae, 1324% corresponding body diameter long, lateral differentiation of body cuticle with only slightly coarser punctations, spiral amphidial fovea with 3 turns, spicules arcuated and 1.31.6 cloacal body diameter long, slightly arcuated gubernacular apophyses, and twelve precloacal supplements, in the form of small pores. Sabatieria multipora sp. nov. is characterized by body length 21392324 m, short cephalic setae (47 m long, 3040% corresponding body diameter long), cuticle with lateral differentiation of distinctly coarser punctations extending from anterior edge of amphidial fovea to anterior of intestine and in the tail region, spiral amphidial fovea with 3 turns, males with spicules 1.92.0 cloacal body diameter long, seventeen fine tubular precloacal supplements with distance between adjacent supplements increasing towards anterior, and with curved gubernacular apophyses. We obtained 18S rDNA and 28S rDNA sequences from the two new species, which are both closely related to other species of Sabatieria. Our analyses also show that several genera of Comesomatidae Filipjev, 1918 do not form monophyletic clades.

Review of Euchromadorinae (Nematoda: Chromadorida) with description of a new species of Trochamus Boucher & De Bovée, 1971 from the Sundarban, India.

Diagnostic characters for all 11 valid genera of Euchromadorinae are presented with taxonomic key on the basis of morphology of male copulatory apparatus, cuticular pattern, amphideal fovea, and buccal onchia. The key to the species of Trochamus spp. is also constructed with the description of T. timmi sp. n. from the mud-flat of Sundarban, India. The newly described species is different from other Trochamus spp. on the basis of the appearance of lateral differentiation of cuticle, long curved spicule, simple gubernaculum and the presence of pre-cloacal modification in male.

Descriptions of Leptolaimus sinensis sp. nov. and Perspiria brevicaudata sp. nov. (Nematoda) from the Yellow Sea, China.

Two new free-living marine nematodes which were collected at silt beach of Rizhao along the Yellow Sea are identified here as Leptolaimus sinensis sp. nov. and Perspiria brevicaudata sp. nov. Leptolaimus sinensis sp. nov. is characterized by annulated cuticle with lateral alae, 2 µm in width; buccal cavity cylindrical; cephalic setae 2 µm long; amphidial fovea unispiral, circular in outline; six to seven evenly spaced tubular precloacal supplements and 23-29 continuous alveolar supplements extending from cloaca to level of the base of buccal cavity; spicules slender, slightly arcuate; gubernaculum with dorso-caudal apophysis; tail conico-cylindrical, about 6 times cloacal body diameter in males and elongated in females, about 9 times anal body diameter in length. Perspiria brevicaudata sp. nov. is characterized by having four cephalic setae and four cervical setae; small buccal cavity with dorsal tooth and minute ventral tooth; amphidial fovea unispiral, looking like double circle in outline, surrounded partially by cuticle striations; spicules arcuate with ventral velum, handle-like proximally and tapered distally; gubernaculum plate-shaped, without apophysis; twelve winged precloacal supplements present. Updated identification keys for group of Leptolaimus species characterized by the presence of both alveolar and tubular precloacal supplements and for species of Perspiria are also given.

Description of two new species of Nematoda: Litinium macramphida sp. nov. (Oxystominidae) and Cyartonema breviseta sp. nov. (Cyartonematidae) from the Yellow Sea, China.

Two new species of Nematoda, Litinium macramphida sp. nov. and Cyartonema breviseta sp. nov. are described from the Yelllow Sea. Litinium macramphida sp. nov. is characterized by body relatively long, inner and outer labial sensilla setiform with same length, amphideal fovea large and drop-shaped with amphideal aperture ovoid, spicules short and wide, gubernaculum simple and boat shaped, two precloacal supplements, and tail conical with rounded tip. Cyartonema breviseta sp. nov. is characterized by body short and slender, four cephalic sensilla papilliform, amphideal fovea circular and large, spicules curved and sickle-shaped, gubernaculum with dorsal-caudal apophysis and posterior end anteriorly hooked, and tail conical.

Two new species of Cyatholaimidae (Nematoda: Chromadorida) from the Southeastern Brazilian coast with emphasis on the pore complex and lateral pore-like structures.

Cyatholaimidae is a common and diverse family of mainly marine nematodes, potentially, with a large number of species to be discovered. The taxonomy of the group is marked by a lack of information about the evolutionary history of the characters and of detailed descriptions of morphological structures that may be taxonomically relevant. Two new species of the family are described from a sublittoral region in Southeastern Brazil, emphasizing the importance of the distribution and morphology of pore complex and pore-like structures present on the cuticle. The taxonomic importance of the cuticle ornamentation and spicule shape for the Biarmifer species, as well as the precloacal supplements structures of Pomponema species, are discussed. Biarmifer nesiotes sp. nov. differs from other species of the genus by the presence of eight longitudinal rows of pore complex on the cuticle and by the shape of the copulatory structure. Pomponema longispiculum sp. nov. differs from the most similar species, P. stomachor Wieser, 1954, by the smaller number of turns of the amphidial fovea, the shorter tail and the beginning of the cuticle lateral differentiation (3/4 of the pharynx length vs. end of the pharynx, respectively). We also obtained the SSU rDNA sequence from Pomponema longispiculum sp. nov., which is closely related to Pomponema sp. (MN250093) by about 91%. Updated tabular keys to species identification of each genus (Biarmifer and Pomponema) are included, containing morphometric data, characters related to cuticle ornamentation, and copulatory structures.

Machine learning algorithms accurately identify free-living marine nematode species.

Background: Identifying species, particularly small metazoans, remains a daunting challenge and the phylum Nematoda is no exception. Typically, nematode species are differentiated based on morphometry and the presence or absence of certain characters. However, recent advances in artificial intelligence, particularly machine learning (ML) algorithms, offer promising solutions for automating species identification, mostly in taxonomically complex groups. By training ML models with extensive datasets of accurately identified specimens, the models can learn to recognize patterns in nematodes' morphological and morphometric features. This enables them to make precise identifications of newly encountered individuals. Implementing ML algorithms can improve the speed and accuracy of species identification and allow researchers to efficiently process vast amounts of data. Furthermore, it empowers non-taxonomists to make reliable identifications. The objective of this study is to evaluate the performance of ML algorithms in identifying species of free-living marine nematodes, focusing on two well-known genera: Acantholaimus Allgén, 1933 and Sabatieria Rouville, 1903. Methods: A total of 40 species of Acantholaimus and 60 species of Sabatieria were considered. The measurements and identifications were obtained from the original publications of species for both genera, this compilation included information regarding the presence or absence of specific characters, as well as morphometric data. To assess the performance of the species identification four ML algorithms were employed: Random Forest (RF), Stochastic Gradient Boosting (SGBoost), Support Vector Machine (SVM) with both linear and radial kernels, and K-nearest neighbor (KNN) algorithms. Results: For both genera, the random forest (RF) algorithm demonstrated the highest accuracy in correctly classifying specimens into their respective species, achieving an accuracy rate of 93% for Acantholaimus and 100% for Sabatieria, only a single individual from Acantholaimus of the test data was misclassified. Conclusion: These results highlight the overall effectiveness of ML algorithms in species identification. Moreover, it demonstrates that the identification of marine nematodes can be automated, optimizing biodiversity and ecological studies, as well as turning species identification more accessible, efficient, and scalable. Ultimately it will contribute to our understanding and conservation of biodiversity.

Three new free-living marine nematode species of the family Comesomatidae from Mangrove wetlands in Jinmen County, Taiwan.

Three new free-living marine nematodes, belonging to the genera Dorylaimopsis, Comesoma and Paracomesoma are described from the mangrove wetlands of western Taiwan Island. Dorylaimopsis jinmendaoica sp. nov. is characterized by having a cuticle with lateral differentiation of longitudinal rows of two rows of larger dots in the middle of the body, a spiral amphideal fovea with 2.52.75 turns, excretory pore anterior to nerve ring and 1721 fibriform precloacal supplements. Comesoma quattuordecimsupplementata sp. nov. is characterized by having a spiral amphideal fovea with 2.52.75 turns and 14 fibriform precloacal supplements. Paracomesoma paralissum sp. nov. is characterized by having a spiral amphideal fovea with 3.0 turns and 40 fibriform precloacal supplements. Differentiating characteristics of all known male Dorylaimopsis, Comesoma and Paracomesoma species are also given.

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.