Systematics Of Nematodes Research Articles

Phylum Nematoda: a classification, catalogue and index of valid genera, with a census of valid species.

A classification of the entire Phylum Nematoda is presented, based on current molecular, developmental and morphological evidence. The classification reflects the evolutionary relationships within the phylum, as well as significant areas of uncertainty, particularly related to the early evolution of nematodes. It includes 3 classes, 8 subclasses, 12 superorders, 32 orders, 53 suborders, 101 superfamilies, 276 families, 511 subfamilies, 3030 genera, and 28537 species. All valid species named from the time of publication of the previous classification and census (2010) to the end of 2019 are listed, along with the number of valid species in each genus. Taxonomic authorities are provided for taxon names of all ranks. The habitats where the species in each genus are found are listed, and an alphabetic index of genus names is provided. The systematics of nematodes is reviewed, along with a history of nematode classification; evolutionary affinities and origins of nematodes; and the current diagnosis of the group. Short overviews of the general biology, ecology, scientific and economic importance of the group are presented.

The complete mitochondrial genome of capillariid nematodes (Eucoleus annulatus): A novel gene arrangement and phylogenetic implications

Capillariid nematode is a group of endoparasites of vertebrates with a complex taxonomy, causing significant economic losses to poultry industry. The taxonomic status of the genus Eucoleus remained controversial for several decades. Mitochondrial (mt) DNA provides useful genetic markers for accurate identification of species, but complete mt genome sequences have been lacking for any Capillariid nematodes. In the present study, we decoded the complete mt genome of E. annulatus and examined its phylogenetic relationship with selected members of the class Enoplea nematodes. The circular mt genome of E. annulatus was 14,118 bp, encoded 37 genes with a single non-coding region and showed substantial gene rearrangements (especially tRNA genes) compared to other nematodes studied to date. The complete mt genome of E. annulatus showed a clear A + T bias in nucleotide composition. The number of A (5404) was approximately equal to T (5405) and the GC-skew was negative on average (−0.073). Phylogenetic analyses based on 18S rDNA placed Eucoleus spp. well apart from each other and supported the proposal that Eucoleus and Capillaria are two distinct genera. Similarly, Bayesian inference (BI) and Maximum likelihood (ML) phylogenies based on mtDNA sequences revealed that the family Capillariidae is more closely related to the family Trichuridae than to the family Trichinellidae. This is the first report of the complete mt genome of capillariid nematodes, and it will provide additional genetic markers for studying the molecular epidemiology, population genetics and systematics of capillariid nematodes and should have implications for the molecular diagnosis, prevention, and control of capillariosis in animals.

Evaluation and utility of mitochondrial ribosomal genes for molecular systematics of parasitic nematodes

BackgroundMolecular advances have accelerated our understanding of nematode systematics and taxonomy. However, comparative analyzes between various genetic markers have led to discrepancies in nematode phylogenies. This study aimed to evaluate the suitability of using mitochondrial 12S and 16S ribosomal RNA genes for nematode molecular systematics.MethodsTo study the suitability of mitochondrial 12S and 16S ribosomal RNA genes as genetic markers for nematode molecular systematics, we compared them with the other commonly used genetic markers, nuclear internal transcribed spacer 1 and 2 regions, nuclear 18S and 28S ribosomal RNA genes, and mitochondrial cytochrome c oxidase subunit 1 gene. After that, phylum-wide primers for mitochondrial 12S and 16S ribosomal RNA genes were designed, and parasitic nematodes of humans and animals from 75 taxa with 21 representative species were inferred through phylogenetic analyzes. Phylogenetic analyzes were carried out using maximum likelihood and Bayesian inference algorithms.ResultsThe phylogenetic relationships of nematodes based on the mitochondrial 12S rRNA gene supported the monophyly of nematodes in clades I, IV, and V, reinforcing the potential of this gene as a genetic marker for nematode systematics. In contrast, the mitochondrial 16S rRNA gene only supported the monophyly of clades I and V, providing evidence that the 12S rRNA gene is more suitable for nematode molecular systematics. In this study, subclades of clade III containing various nematode families were not monophyletic when the 16S or 12S rRNA gene was used as the genetic marker. This is similar to the phylogenetic relationship revealed by previous studies using whole mitochondrial genomes as genetic markers.ConclusionsThis study supports the use of the 12S rRNA gene as a genetic marker for studying the molecular systematics of nematodes to understand intra-phyla relationships. Phylum-wide primers for nematodes using mitochondrial ribosomal genes were prepared, which may enhance future studies. Furthermore, sufficient genetic variation in the mitochondrial 12S and 16S rRNA genes between species also allowed for accurate taxonomy to species level, revealing the potential of these two genes as genetic markers for DNA barcoding.

Complete mitochondrial genome of Angiostrongylus malaysiensis lungworm and molecular phylogeny of Metastrongyloid nematodes

Angiostrongylus malaysiensis is a nematode parasite of various rat species. When first documented in Malaysia, it was referred to as A. cantonensis. Unlike A. cantonensis, the complete mitochondrial genome of A. malaysiensis has not been documented. We report here its complete mitogenome, its differentiation from A. cantonensis, and the phylogenetic relationships with its congeners and other Metastrongyloid taxa. The whole mitogenome of A. malaysiensis had a total length of 13,516bp, comprising 36 genes (12 PCGs, 2 rRNA and 22 tRNA genes) and a control region. It is longer than that of A. cantonensis (13,509bp). Its control region had a long poly T-stretch of 12bp which was not present in A. cantonensis. A. malaysiensis and A. cantonensis had identical start codon for the 12 PCGs, but four PCGs (atp6, cob, nad2, nad6) had different stop codon. The cloverleaf structure for the 22 tRNAs was similar in A. malaysiensis and A. cantonensis except the TΨC-arm was absent in trnV for A. malaysiensis but present in A. cantonensis. The Angiostrongylus genus was monophyletic, with A. malaysiensis and A. cantonensis forming a distinct lineage from that of A. costaricensis and A. vasorum. The genetic distance between A. malaysiensis and A. cantonensis was p=11.9% based on 12 PCGs, p=9.5% based on 2 rRNA genes, and p=11.6% based on 14 mt-genes. The mitogenome will prove useful for studies on phylogenetics and systematics of Angiostrongylus lungworms and other Metastrongyloid nematodes.

One new genus and five new nematode species (Monhysterida, Xyalidae) from Tonga and Kermadec Trenches, Southwest Pacific.

Little is known about the diversity and systematics of nematodes in hadal trenches (>6000 m depth). The analysis of core samples recently obtained from Tonga (10810 m) and Kermadec Trenches (8081 m) reveals the presence of a diverse nematode community in these extreme environments, and provides the deepest record for the phylum. Here, one new genus and five new species of the family Xyalidae are described. Lamyronema n. gen. is characterised by a large, tripartite buccal cavity and can be distinguished from other genera with similar buccal cavities mainly by the pharyngeal tissue almost completely surrounding the buccal cavity and by the presence of sub-cephalic setae positioned anteriorly to the amphideal fovea. Lamyronema horizonensis n. gen. n. sp. is characterised by the presence of 16-22 sub-cephalic setae, pronounced sexual dimorphism in the size of the amphideal fovea, and short, straight spicules. Daptonema amphorum n. sp. is characterised by short somatic setae, narrow head region, amphideal fovea relatively far from anterior body extremity, thin gubernaculum without apophyses, and cuticularised prevulvar uterine sac with two conspicuous rims. Manganonema kitasatoi n. sp., M. rowdeni n. sp., and M. majusculum n. sp. share traits that set them apart from other species of the genus, i.e., large body size (1100-2080 µm), presence of one pair of short setae posterior to the amphideal fovea, and male reproductive system with two testes. The latter trait necessitates amendments to the genus diagnosis.

Systematics and DNA barcoding of free-living marine nematodes with emphasis on tropical desmodorids using nuclear SSU rDNA and mitochondrial COI sequences

The diversity and phylogenetic relationships of the Desmodoridae, a widespread tropical family of free-living marine nematodes, is hitherto poorly known both from molecular and taxonomic points of view. We performed a molecular phylogenetic analysis of marine nematodes to: i) disentangle relationships among tropical desmodorid species; and ii) compare the performance of the nuclear SSU rDNA and mitochondrial COI nucleotide sequences in 42 and 45 nominal species, respectively, to identify species. We generated 27 new sequences of SSU rDNA belonging to five genera not previously sequenced, and 34 new sequences of COI belonging to six genera and four families not previously sequenced. The SSU rDNA tree confirmed the Enoplida to be a monophyletic sister group to the Chromadorida. The family Comesomatidae is a sister group of the Xyalidae within the Monhysterida. Both DNA markers confirmed the congruence between the morphology- and molecular-based phylogenetic inferences for most of the families. Desmodoridae was a monophyletic group, but the relationships within the family could not be recovered; the subfamilies Desmodorinae and Spiriniinae were not monophyletic meanwhile the monophyly of Stilbonematinae was not fully supported due to a few specimens of questionable identity. COI performed better than SSU rDNA to disentangle relationships among closely related species and suggested the presence of cryptic diversity within Desmodoridae. COI is effective to explore cryptic diversity and barcode species within Nematoda, with a possible threshold of genetic distance of 5% between conspecific and interspecific sequences, but DNA barcoding is limited by the poor knowledge of the diversity and taxonomy of the group and the lack of a good reference database of vouchered COI sequences.

Introduction of Steven A. Nadler, Recipient of the Henry Baldwin Ward Medal for 2013

Introduction of Steven A. Nadler, Recipient of the Henry Baldwin Ward Medal for 2013

Systematics of Cyst Nematodes (Nematoda: Heteroderinae)

Systematics of Cyst Nematodes (Nematoda: Heteroderinae) . Nematology Monographs and Perspectives. Volume 8A, 8B . S.A. Subbotin, M. Mundo-Ocampo, J.B. Baldwin . ( David Hunt, Roland N. Perry ( eds )). 351 pp. 512 pp . Leiden, The Netherlands : Koninklijke Brill NV . 2010 . €139, €149. ISBN 978-90-04-16225 9, ISBN 978-90-04-16434 5 (hardback ). Cyst-forming nematodes are amongst the most economically important plant-parasitic nematodes of cultivated crops in the world, in both temperate and tropical regions. Many cyst nematode species, particularly those belonging to the genera Heterodera and Globodera, are pathogens on several important vegetable and fruit crops (carrot, chickpea, clover, fig, maize, olive, pea, potato, rice, soybean, sugar beet, tobacco, wheat, etc.), causing extensive damage and significant yield loss. Consequently, the accurate and timely identification of cyst nematodes infecting crops is a prerequisite for designing effective management strategies for these pathogens. This book is a useful publication that provides a comprehensive overview and an in-depth summary and review of the systematics and identification of cyst-forming nematodes, and includes research on taxonomy, biology, and methods of biochemical and molecular diagnostics. This book is Volume 8 in the Nematology Monographs & Perspectives series, and comprises two parts, A and B. Throughout its 11 chapters, part A presents summarized and specialized information on various key aspects of different exciting areas of morphology, taxonomy, biology, evolution and systematics. Chapters 1–4 describe the most important diagnostic characters of cyst nematodes, as well as summarized aspects on life cycles, symptoms on parasitized plants, their pathogenic variability (pathotypes), biogeography, methods for applying electron microscopy and biochemical and molecular approaches for diagnostics of cyst nematodes. A DNA-based diagnostic section includes a comprehensive review of genes used for molecular diagnostics, including nuclear RNA and mitochondrial DNA genes, as well as methods such as restriction fragment length polymorphism (RFLP), use of specific primers, and real-time PCR. Chapter 5 comprises general systematics of Heteroderinae, including a useful and practical identification key to genera, and a discussion on species delimitation. Chapters 6–11 deal with the systematics, key to species based on morphological features, molecular characterization, and species description in the genera Globodera, Punctodera, Cactodera, Dolichodera, Betulodera and Paradolichodera. For each species, the complete description of female, cyst, male and second-stage juveniles is provided, together with the type host and other host plants, as well as the distribution, biology, pathogenicity and biochemical and molecular characterization, if available. In addition, this volume is complemented with four useful and practical appendices dealing with methods for soil extraction of cyst nematodes, protocols for preparation of vulval cones, separation of G. pallida and G. rostochiensis by immuno-electro-focusing (IEF), and PCR-ITS-RFLP. Part B is completely dedicated to the genus Heterodera which comprises 80 species, including well known pathogens such as H. schachtii in sugar beet, H. avenae, H. filipjevi and H. hordecalis in cereals, H. ciceri in chickpea, H. cruciferae in crucifers, H. glycines in soybean, H. goettingiana in legumes, H. oryzae and H. oryzicola in rice, H. trifolii in clover and H. zeae in maize. As in part A, a key to species based on morphological features, molecular characterization, and species description, biology, distribution, host, pathogenicity, and biochemical and molecular characterization is provided for each species. The text is well written in both parts, and in their approach and choice of illustrations the authors make this a valuable tool for those involved in the fields of nematology and plant pathology. In summary, the authors are to be congratulated for their initiative and achievement in the production of such an enjoyable book that is the most comprehensive treatise currently available on cyst-forming nematodes and, as such, constitutes a unique and most valuable source of information, and a precious guide to anyone (scientists, teachers, students, extension officers) who is interested in Nematology at large, and in cyst nematodes in particular.

Phylum Nematoda*

The systematics of nematodes is reviewed, including: an overview of the general biology, ecology, scientific and economic importance of the group; a history of classification; evolutionary affinities and origins of nematodes; and the current diagnosis of the group. Alternative classifications within the Phylum Nematoda are discussed, and a classification to family level incorporating the latest molecular, developmental and morphological research is presented. This classification reflects the current views on evolution within the phylum, as well as significant areas of uncertainty, particularly related to the early evolution of nematodes. It includes 5 classes, 9 subclasses, 23 superorders, 39 orders, 52 suborders, 89 superfamilies and 241 families. There are few changes at the superfamily and family levels.

A molecular systematic framework for equine strongyles based on ribosomal DNA sequence data

In this study, molecular data sets were used to address the controversies relating to the systematics of strongyloid nematodes of equids utilising morphological data sets. DNA sequences of the first and second internal transcribed spacers (ITS-1 and ITS-2) of ribosomal DNA were determined for 30 species of equine strongyles and the systematic relationships reconstructed using phenetic and phylogenetic tree-building methods. The molecular data provided support for the hypothesis that the genera with large subglobular buccal capsules are ancestral to those with small cylindrical buccal capsules, but did not provide support for the current division of the subfamilies Strongylinae and Cyathostominae or for some taxonomic groupings (i.e. generic designations of species) within the Cyathostominea based on morphological data. Although not entirely concordant, the current molecular data provide a systematic framework for future studies of equine strongyles, which could be exploited in combination with new, phylogenetically informative morphological data sets.

Differences in the second internal transcribed spacer of four species of Nematodirus (Nematoda: Molineidae)

Genetic differences among Nematodirus spathiger, Nematodirus filicollis, Nematodirus helvetianus and Nematodirus battus in the nucleotide sequence of the second internal transcribed spacer (ITS-2) of ribosomal DNA ranged from 3.9 to 24.7%. Pairwise comparisons of their ITS-2 sequences indicated that the most genetically similar species were N. spathiger and N. helvetianus. N. battus was the most genetically distinct species, with differences ranging from 22.8 to 24.7% with respect to the other three species. Some of the nucleotide differences among species provided different endonuclease restriction sites that could be used in restriction fragment length polymorphism studies. The ITS-2 sequence data may prove useful in studies of the systematics of molineid nematodes.

Systematics of gastrointestinal nematodes of domestic ruminants: advances between 1992 and 1995 and proposals for future research

The systematics of trichostrongyloid nematodes of ruminants provides a foundation for diagnostic and responds to the need to identify eggs in feces, free-living larvae from pastures or fecal cultures and larval or adult nematodes collected from hosts. These needs are associated with diagnostic problems or research projects. Difficulties in identifying all developmental stages of trichostrongyloid nematodes of domestic ruminants still severely limit the effective diagnosis and control of these parasites. Phylogenetic hypotheses as the basis for predictive classifications have been developed only for the subfamilies of the Trichostrongylidae. This report briefly describes recent progress in the development of improved tools for identification, phylogenetic analyses and predictive classifications. It also describes future research needed on the identification and classification of trichostrongyloid nematode parasites of domestic ruminants. Nematodes included are species of the superfamily Trichostrongyloidea known to be important pathogens of domestic ruminants. The information summarized is presented by nematode developmental stage and by taxonomic groups. Eggs: While eggs of some trichostrongyloid nematode parasites of ruminants can be readily identified to their genus ( Nematodirus), and some to species (e.g. Nematodirus battus), most of the important pathogens (including the Ostertagiinae and Haemonchinae) cannot be identified morphologically or morphometrically even to family level. However, DNA technology has been developed for determining not only the presence of specific pathogens in eggs from fecal samples, but also for estimating the percentage of the total eggs that each pathogen comprises. This new method will make possible a rapid determination of which individual animals in a herd should be treated. Larvae: The most commonly-used method for identifying infective larvae is time-consuming (several weeks), unreliable for estimating intensities of individual species as components of mixed populations and requires highly trained specialists. Available identification keys for larvae are not well illustrated and need to be augmented. Adults: Recent advances in the identification of adult trichostrongyloids and their systematics are organized by taxonomic group. Genera included are Ostertagia, Haemonchus, Cooperia, Trichostrongylus and Nematodirus. Recently, the first phylogenetic analysis of the Trichostrongylidae family established monophyly for the family. A similar analysis of the Molineidae is needed. Ostertagia: Several studies of polymorphism summarized the phenomenon and listed 19 polymorphic species in five genera. Two studies of DNA differences within and among polymorphic species of Ostertagiinae supported earlier hypotheses that the species pairs represent polymorphic species. A phylogenetic analysis of the Ostertagiinae and generic concepts are needed. Haemonchus: A key to three species of Haemonchus provides, for the first time, morphological characteristics for the microscopical identification to species of individual adult nematodes of either sex. The Food and Drug Administration is now requiring that results of drug trials include identification of Haemonchus to species. Cooperia: Studies using random amplified polymorphic DNA methods showed a high degree of variation within and among C. oncophora/C. surnabada, but supported a polymorphic relationship for the species pair. A phylogenetic analysis of the Cooperiinae is needed. Trichostrongylus: Restriction Fragment Length Polymorphisms (RFLPs) of genomic DNA of two strains of T. colubriformis indicated a high degree of intra- and inter-strain DNA polymorphism. However, other studies demonstrated expected species level differences between T. colubriformis and T. vitrinus using Random Amplified Polymorphic DNA (RAPD) methods. Sequences of the second Internal Transcribed Spacer Region (ITS-2) ribosomal repeat showed sequence differences of 1.3–7.6% among five well-defined species of Trichostrongylus. This provides a standard for species level differences within the Trichostrongylidae. Nematodirus: The origin of N. battus in the British Isles is still a mystery. Recently, DNA studies have provided evidence that populations on both coasts of the United States originated from Canada. A phylogenetic study of Nematodirus is in progress. Modern systematic methods have not yet been applied to the development of classifications for all subfamilies and most genera of the Trichostrongyloidea. Additional factors complicating these problems are a lack of knowledge of the parasites of wild bovids and cervids, the international transport of wild and domestic hosts and environmental changes that may alter the parasite fauna in a modern farm setting.

The systematics of nematodes that cause ostertagiasis in domestic and wild ruminants in North America: an update and a key to species

Studies of medium stomach worms (Subfamily Ostertagiinae) of domestic and wild ruminants in North America have refined our understanding of the systematics, host distribution and biogeography of these nematodes. Strong support for recognition of monophyly for the Ostertagiinae has resulted from preliminary phylogenetic analyses of morphological characters among these and other trichostrongylids. Evaluation of morphological and biochemical characters in our laboratory and elsewhere has not refuted the polymorphism hypothesis where paired major and minor morphotypes are postulated to represent polymorphic species within the genera Ostertagia (Ostertagia ostertagi/Ostertagia lyrata; Ostertagia leptospicularis/Ostertagia kolchida; Ostertagia gruehneri/Ostertagia arctica; Ostertagia mossi/Ostertagia dikmansi), Teladorsagia (Teladorsagia circumcincta/Teladorsagia trifurcata (=Teladorsagia davtiani), and Marshallagia (Marshallagia marshalli/Marshallagia occidentalis). The minor mophotype of Ostertagia bisonis, recognized in Eurasia (considered to be Teladorsagia kazakhstanica), has yet to be discovered in North America. The taxonomy of these species has remained stable since an earlier overview of Ostertagia spp. and Teladorsagia spp. in North America domestic stock at the 1986 Ostertagia Workshop. Investigations since 1986 have focused on comparative morphology and the clear differentiation of Ostertagiinae, primarily from wild ruminants, that have been reportd or may potentially occur in domestic bovids. Among these are species which infect wild and domestic sheep ( Marshallagia marshalli/Marshallagia occidentalis), bovids ( Ostertagia bisonis), and cervids ( Ostertagia mossi/Ostertagia dikmansi, Ostertagia leptospicularis/Ostertagia kolchida, Ostertagia gruehneri/Ostertagia arctica, Mazamastrongylus odocoilei and Mazamastrongylus pursglovei) in North America. A key is presented for identifying 5 species of the Subfamily Ostertagiinae that are parasitic in domestic and wild ruminants of North America. Four exotic species ( Camelostrongylus mentulatus, Spiculopteragia spiculoptera (=Spiculopeteragia boehmi), Spiculopteragia asymmetrica and Longistrongylus curvispiculum) have been reported in North America, but only in game farms and are not included in the key. Hyostrongyus rubidus, a member of the Ostertagiinae normally parasitic in pigs and only rarely reported from domestic ruminants, is not included in the keys. Additional data from comparative morphology and molecular analyses will promote a reassessment of the generic-level systematics of the Ostertagiinae and allow an evaluation of host-parasite evolution and historical biogeography.

Studies on the Morphology and Systematics of Plant and Soil Nematodes mainly from Andhra Pradesh. I. Tylenchoidea

SummaryDescriptions of four new tylenchs belonging to different genera are given : (1) Tylenchus (Tylenchus) holochmatus n.sp., (2) Tylenchorhynchus varicaudatus n.sp., (3) Trichotylenchus trilokiae n.sp., (4) Helicotylenchus pteracercus n.sp. The material of the first described species was collected in North India and that of the other new species in South India. Systematic features of new species are fully discussed and compared with those of the related forms.Detailed descriptions are given of Tylenchorhynchus digitatus and Pratylenchus indicus described by Das (I960) from Hyderabad. The material was collected from type locality but from different hosts. Tylenchorhynchus curvus Williams, 1960, is recorded from India.Species reported as causing damage to economically important plants in Hyderabad are : Hoplolaimus seinhorsti Luc, 1958, parasitic in cauliflower; Pratylenchus thornei Sher and Allen, 1953, parasitic in maize and Rotylenchulus reniformis Linford and Oliveira, 1940, parasitic in grape vines.

Addition to the Explanation of Systematics of Nematodes Parasitic in the Frontal Sinus and Lungs ofMustelidae

Addition to the Explanation of Systematics of Nematodes Parasitic in the Frontal Sinus and Lungs of<i>Mustelidae</i>