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Morphology of the family Plectidae Örley, 1880: Plectus communis Bütschli, 1873 (A, Q, V), P. velox Bastian, 1865 (B, M, T), P. parietinus Bastian, 1865 (C, N), Ceratoplectus assimilis (Bütschli, 1873) Andrássy, 1984 (D, E, J, W), P. geophilus de Man, 1880 (F, K, R), P. parvus Bastian, 1865 (G, P, S), P. minimus Cobb, 1893 (H, L, U), P. decens Andrássy, 1985 (I, O, X). (A-C, F-I) Anterior end, combined view; (D) Labial region, surface view; (E) Anterior end, median section; (J-Q) Vagina region; (R-X) Posterior part of pharynx, renette, coelomocytes. Scale bar 20 µm.
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The phylogeny and classification of the superfamily Plectoidea Örley, 1880 is revised on the basis of published and updated morphological data for 35 ingroup and 2 outgroup species. The following features are here considered to support the monophyletic origin of the superfamily: 1) stegostom developed and differentiated into two sections; 2) dorsal...
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Context 1
... multispinatoides Heyns et Coomans, 1983: 3♀♀, 1♂, USA, Georgia, Tifton, wet meadow, Fig. 5 Ley (2005); additional data taken from Heyns and Coomans ...
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... gracilicaudatus has a broad cheilostom surrounded by leaf-shaped lips with strongly sclerotized rounded cheilorhabdia located in the proximal part of the cheilostom (Fig. 4 G). Among the Plectus-species, P. andrassyi, P. aquatilis, P. cancellatus, P. communis, P. decens, P. geophilus, P. longicaudatus, P minimus, P. murrayi, P. paracuminatus, P. parietinus, P. parvus, P. pusteri and P. velox have small bar-or granule-shaped cheilorhabdia (Figs 5 A-C, F-I). Presence of cheilorhab- dia may be interpreted as an additional support which function is uncertain. ...
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... gymnostom in all species of Plectoidea is a cylin- drical, conical or barrel-shaped structure with strongly sclerotized walls, with the exception of Anaplectus, which has bar-shaped cheilorhabdia, and Ceratoplectus assimilis, which has small and oval cheilorhabdia (Fig. 5 E). Both the latter cases are probably derived conditions. The stegostom is visibly subdivided into two subsections, of which the posterior one is nar- row and penetrated by the dorsal gland orifice in all species. The anterior stegostom section is narrow in Pakira orae (Fig. 1 C) and Perioplectus labiosus; funnel- shaped in Arctiplectus ...
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... members of the superfamily Plectoidea are characterised by rather similar pharynges. It is subdi- vided into corpus and postcorpus by a discontinuity in the muscular tissue and subventral gland orifices, the postcorpus is composed of a cylindrical isthmus and an oval or pear-shaped basal bulb, which is terminal or subterminal in position, e.g. a postbulbal prolongation that is half as long as the bulb itself is present in Plectus decens, P. geophilus, P. longicaudatus and P. minimus (Figs 5 R, U, X). Furthermore, the basal bulb holds a valvular apparatus with transverse denticulate plates and a posterior sclerotized haustrulum-like structure (here named "plectoid valve"). ...
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... the other hand the pars distalis vaginae in several species of Plectus is modified into a pair of sclerotized folds, the so-called epiptygmata. Among studied species, epiptygmata were found in Plectus andrassyi, P. cancellatus, P. communis, P. murrayi, P. paracuminatus, P. parietinus, P. pusteri and P. velox ( Figs 5 M-N, Q). Although, the function of epiptygmata is unclear, I consider its presence to be a derived trait. ...
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... sphincter is most common and here considered as ancestral, characteristic for all but some species of Plectus, viz. P. aquatilis, P. cancellatus, P. andrassyi, P. paracuminatus, P. parietinus, P. murrayi, P. pusteri and P. velox ( Figs 5 M-N, Q). Both the pres- ence of epiptygmata and/or two vaginal sphincters are treated here as derived features. ...
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... Historically, classification of this taxon was the most controversial in nematodes and still remains unsettled. The most recent classification at an order and family level (De Ley & Blaxter 2002, 2004) is a tentative combination of early molecular phylogenies (Blaxter et al. 1998) with morphological cladograms deduced by . Its present systematic position and members ranking was assessed mostly on the basis of only one family, Plectidae Ö rley, 1880, which with members of the genera Plectus Bastian, 1865 and Tylocephalus Crossman, 1933 were used in molecular phylogeny (Blaxter et al. 1998). ...
... Certain families were included in the group by some authors and excluded by others (like Teratocephalidae Andr é ssy, 1958, Peresianiidae Vitiello & De Coninck, 1968, etc.) justified by morphological similarity, and not by the phylogenetic relationships . The first detailed phylogenetic analyses of many species and genera of the suborder Plectina were based on morphological characters (Holovachov 2004, Holovachov & Bostr ö m 2004). The authors pinpointed multiple problems with potential paraphyly, unclear character polarity and convergence. ...
... The rare cases of three or even two " post-hatching " juvenile stages in saprobiotic and parasitic Rhabditida appear when the first (and sometimes the second) moult takes place inside the egg before hatching (Malakhov 1986 ). Four juvenile stages were observed in both studied species of the genus Pakira, in Hemiplectus muscorum, Anaplectus grandepapillatus, Plectus parietinus, P. australis and P. antarcticus (Holovachov 2004; Holovachov et al. 2009 ). However, many species of Plectidae were found to have only three morphologically distinct juvenile stages, instead of four. ...
... The first extensive study of the genus Plectus was presented by Maggenti (1961), then other scientists added more information about taxonomy of the genus (e.g., Andrássy 1985Andrássy , 1998Andrássy , 2005Zell 1993;De Ley & Coomans 1994). Detailed phylogenetic analysis of this group was performed by Holovachov (2004), supplemented with new data on morphology and development of the superfamily PlectoideaÖrley, 1880. Van Megen et al. (2009) confirmed the monophyletic origin of the family Plectidae based on SSU rDNA. ...
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Three species of Plectus Bastian, 1865 viz., P. aquatilis and P. pusillus from Kerman province and P. velox from Alborz province, Iran are described and illustrated. Partial sequences of 18S region of ribosomal DNA gene were amplified for P. aquatilis and P. pusillus. The Blast results of population of P. aquatilis from Iran showed 8–10 nucleotides differences with populations of the same species (AF036602; GQ892827; AY284700) reported from the UK, Belgium and The Netherlands, respectively. Whereas Iranian population of P. pusillus showed 14–16 nucleotides differences with P. cf. pusillus (AY284705; AY284704) reported from The Netherlands. Molecular analysis revealed close relationship of the Iranian plectids with P. cf. parvus (AY284699) reported from The Netherlands. Phylogenetic relationships with other related species in the genus Plectus and closely related genera that are available in the GenBank are given.
... From observation, and inferred from body size measurements, some longidorids pass through only three juvenile stages rather than the four stages documented for Tylenchida and assumed for many other soil nematodes (Yeates and van Etteger, 1991;Halbrendt and Brown, 1992). However, three juvenile stages are reported in several genera of the Plectidae (Holovachov, 2004), and completion of the J1 stage within eggs of some Tylenchida could be construed as a trend towards shortening the life cycle. The loss of a developmental stage has been considered to result from hormonally-mediated heterochrony (Robbins et al., 1995. ...
... Features are sometimes observed in nematodes that appear to be developmental abnormalities rather than indicators of plasticity or mutation and the occurrence of an additional odontostyle might fall into that category. For example, the occasional occurrence of two or more vulvas in longidorids (Fig. 4) (Robbins, 1986;Robbins and Rubtsova 1996;Rubtsova et al., 1999;Kumari and Decraemer, 2006), the observation of specimens with two and three vulvas in Mesodorylaimus bastiani (Valocká and Sabová, 1980), differences in number of supplements in males of some Plectus species (Holovachov, 2004), and other examples in mononchids and tylenchids as reviewed by Kumari and Decraemer (2006). Abnormalities in development of the vulva are well understood in hermaphrodites of Caenorhabditis elegans. ...
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Detailed descriptions of six species of Plectus reported for the first time from India are given on the basis of LM and SEM observations. Plectus geophilus de Man, 1880, P. aquatilis Andrássy, 1985, P. parvus Bastian, 1865, P. minimus Cobb, 1893, P. magadani Kuzmin, 1979 and P. communis Bütschli, 1873 are described and illustrated. The salient morphological characters of the species are given. The taxonomy of the genus has been discussed along with the status of species presenting a great degree of morphometric overlap and continuous variation. An emended diagnosis of the genus is provided with incorporation of relatively consistent and less variable characters.
Taxonomic resolution is a critical component of biodiversity assessments. In this case study, we examined a single taxon within a larger study of nematode diversity to evaluate the taxonomic resolution of different diversity assessment methods. The selected taxon was the microbial-feeding genus Plectus, a group considered to include multiple cosmopolitan species. The methods included a morphological evaluation by light microscopy, Sanger sequencing of PCR amplicons of COI and 18S gene regions, and 18S metabarcoding sequencing. The study sites were 15 remnant tallgrass prairie plots in eastern Nebraska. In the morphological analysis, we observed two basic morphotypes, a short-tailed form with a small amphid and a long-tailed form with a large amphid. Sanger sequencing of COI sorted Plectus diversity into six distinct clades. The largest two of these six clades keyed to P. parietinus and P. rhizophilus based on morphology. BLAST analysis with COI revealed no close matches in GenBank. Sanger sequencing of the 18S region did not differentiate the six clades. These results illustrate that the method of diversity assessment strongly influences estimates of biodiversity. An additional 95 Plectus specimens, from outside the remnant sites, added taxonomic breadth to the COI phylogenetic tree. There were no geographically widespread COI haplotypes and no evidence of cosmopolitan Plectus species.
Nematodes are a large and diverse monophyletic taxon with about 20,000 known species. They are part of the taxon Ecdysozoa, some of which possess a characteristic type of brain called the cycloneuralian brain. Because animals with a cycloneuralian brain likely are not a monophyletic group, it is important to describe and understand the structure of cyloneuralian brains and associated nervous system structures. With respect to nematodes, most studies focus on model organisms, such as Caenorhabditis elegans and immunohistochemical data in general, are rare. To expand the knowledge, we investigated two species of the family Plectida, Plectus acuminatus and Plectus aquatilis by immunohistochemical experiments combined with confocal laser-scanning microscopy. In comparison with C. elegans and further nematodes, our results reveal a conserved architecture of the nervous system and several structures can be homologized with known counterparts. Nevertheless, in detail, some striking differences can be demonstrated, which become visible in the arrangement of longitudinal and transverse neurites as well as in specialized neurons, such as the neurosecretory motor neurons within the pharynx. Compared to C. elegans, the branching pattern of these neurons in Plectus spp. is more complex. Overall, there are indications that the nervous system among nematodes is more diverse in structure than originally expected and further studies on taxonomically basal, free-living nematodes needs to be in focus on future investigations.
Descriptions of three known species of Cynura, i.e., C. cerambus, C. klunderi and C. papillata, are given, including SEM micrographs of C. cerambus and a tabular compendium for all species of the genus. The phylogenetic relationships of C. klunderi are inferred from molecular data. Bayesian analyses of small subunit (SSU) of rRNA sequences support a position nested among the Plectidae suggesting the secondary simplification in the morphology of pharyngeal valvular apparatus in Cynura and the 'return' from a terrestrial to a marine environment in this genus.
Secondary succession of nematodes was studied in 1–48-year-old abandoned fields on cambisols in South Bohemia, Czech Republic, and compared with cultivated field and sub-climax oak forests. Bacterivores were the predominant group in the cultivated field whereas in forests root-fungal feeders (mainly Filenchus) were almost as abundant as bacterivores. The total abundance of nematodes in the cultivated field averaged 868×103indm−2. During the first three years of succession the abundance practically did not change (775×103indm−2), the fauna was still similar to that in cultivated field but the biomass increased mainly due to Aporcelaimellus. Then the abundance increased up to 3731×103indm−2 in 7–8-year-old abandoned fields, plant parasites (Helicotylenchus) dominated and the fungal-based decomposition channel was activated. Later the abundance stabilised at between 1086 and 1478×103indm−2 in 13–25-year-old successional meadow stages with high population densities of omnivores and predators. The total abundance of nematodes was low in the 12–13-year-old willow shrub stage (594×103indm−2), increased in the 35–48-year-old birch shrub stage (1760×103indm−2) and the nematode fauna developed towards a forest community. The diversity and maturity of nematode communities generally increased with the age of abandoned fields but the highest values were in meadow stages (81–113 species, 57–68 genera, MI 2.73–3.30). The development of meadow arrested succession towards forests or diverted succession towards a waterlogged ecosystem. The succession of nematodes was influenced by the method of field abandonment (bare soil vs. legume cover, mowing) that affected the formation of either a shrub or meadow stage, and by the soil water status. The composition of the nematode fauna indicated that the soil food web could recover faster from agricultural disturbance under successive meadows than under shrubs.
Nematodes constitute one of the largest animal phyla. Hitherto about 20.000 species have been described but there are estimates that this number is less than 2% of the total number of existing species. Although the larger animal and human parasites were known since ancient times the description of free living nematodes and plant parasites started around 1850. Although nematodes can be found in almost every habitat, they are still one of the least known groups of extant metazoans. In a hierarchical organisation (classification) of nematodes, as for some other groups of multicellular animals, the higher the level, the greater the confusion and discrepancy among different opinions. It is clear, that the applied, prognostic and educational value of such artificial classification is low and requires further improvement.This thesis represents a small brick in the castle of humans' knowledge about nematode morphology, diversity and phylogeny. The author brings to light some new data and ideas about the form of some nematodes, how they develop and how they apparently evolved. Four main chapters deal with one of the smallest but morphologically and ecologically diverse orders, Plectida, whose members are found in marine, terrestrial and fresh water habitats.At the first stage of studies, just one genus, Anonchus, is analysed. Among the six known species included in the analysis, however, Anonchus shows considerable variability in morphology of reproductive organs, of both females and males. It is worth mentioning that morphological peculiarities of female gonads and the male copulatory apparatus are often used to separate populations into different species and to create higher taxonomic categories. The discovery of two new species, A. venezolanw and A. winiszewskae, adds even more to understanding the structural diversity of this genus. The analysis of the morphology of Anonchus species results in considerable rearrangement of the classification of this genus and its allies, which are placed in the newly reinstated family Aphanolaimidae.The main objective of the third chapter was to uncover the morphological diversity of representatives of mostly marine and presumably primitive groups of Plectida, and to propose a phylogenetic hypothesis of their relationships with each other and with their terrestrial allies (descendants ?). Additional descriptions are given for five species. Morphological and taxonomic analysis has been followed by the discovery of new taxa; the description of one, Paraplectonema loofi, is given in this chapter. Another, Procamacolaimus dorylaimus, is described in a separate article, but is also included in the phylogenetic reconstructions, which, on the whole, include 20 in-group laxa representing all distinct genera. A thorough systematic study required at least a brief discussion of phylogenetic affinities of the families Bastianiidae and Odontolaimidae and the genus Tobrilia which were previously included in the order Plectida. The taxonomic position of these taxa has become clearer in light of the new morphological data, particularly in the structure of male copulatory apparatus.The subsequent part of the thesis deals with the few species of the subfamily Wilsonematinae, whose members are one of the smallest terrestrial nematodes. The taxonomy of the Wilsonematinae has been severely hampered by the limits of light microscopy for correct observation and interpretation of their highly elaborate, complex labial region. The discrepancy between recent data and previous published descriptions of the structure of the labial region illustrates the great importance of scanning electron microscopy (SEM) for morphological and taxonomic studies of the group in question. Keeping this in mind, the author provides detailed redescriptions of five species of the genera Wisonema, Ereptonema and Neotylocephalus on the basis of both type and new material from diverse habitats and localities throughout the world. Reappraisal of the earlier morphological descriptions of these taxa resulted in substantial changes in their classification, and critical revision of all allied species and genera. Ultrastructural studies (SEM) made it possible to propose a phylogenetic hypothesis for the subfamily Wilsonematinae.The fifth chapter of this thesis includes a phylogenetic analysis of the largest terrestrial taxon of the order Plectida, superfamily Plectoidea. This analysis is based on published and updated morphological data for 35 in-group species. One of these species will be described as new in a separate publication. To better understand the character polarity, the postembryonic development of four species is described in detail. It was found that not only the general growth and development of reproductive system occurs during postembryonic development but that somatic sensilla, digestive and excretory systems also change morphologically during successive stages. Possible historical relationships of the superfamily Plectoidea are analysed using different methods and principles; one of the phylogenetic hypotheses was selected for thorough discussion, and as a basis for the revised classification of this taxon. Morphological data, which are elucidated and summarised in this chapter, provide the basis to further speculate on structural evidence for parthenogenetic reproduction in one of the studied genera, and the data also suggest several probable ways of niche partitioning in the superfamily Plectoidea.The general discussion summarises all taxonomic changes and suggestions proposed in preceding chapters, and gives a revised and updated classification of the order Plectida. Possible morphological adaptations to the fresh water habitat and structural changes associated with the soil habitat are briefly discussed based on the proposed phylogenetic hypothesis. Since family Plectidae sometimes has been suggested to be closely related to the scientifically and economically important order Rhabditida (=Secernentea), the author proposed that morphology of plectid genus, Anaplectus, may be a source for future research on the origin and evolution of rhabditids.
This book contains 22 chapters on various aspects of freshwater nematode ecology and taxonomy. Subjects covered include the techniques for processing freshwater nematodes, the composition and distribution of free living freshwater nematodes, their abundance, biomass and diversity, the production of freshwater nematodes, their feeding ecology, patterns in size structure of freshwater nematode communities, different nematode habitats, and computation and application of nematode community indices. It provides descriptions with figures of each taxon at the genus level and above to currently valid genera. For every genus, a complete list of species, with an emphasis on biogeography, is given for primarily freshwater taxa and a list of only those species reported from freshwater bodies is given for the genera that are considered primarily non-freshwater. This book is intended to provide a useful reference to students, beginners and established researchers in the field of freshwater nematology, benthologists, invertebrate biologists, limnologists, ecologists, microbiologists and soil biologists.
