Redescription of three pinworms of the genus Cephalobellus Cobb, 1920 (Nematoda: Oxyuridomorpha: Thelastomatidae) from scarab beetle grubs from Hungary.

Larvae of European rose chafer Cetonia aurata (Linnaeus, 1758) and cockchafer Melolontha sp. beetles were collected in Hungary for parasitological study. Intestinal examination revealed the presence of three well-known thelastomatid nematodes belonging to the genus Cephalobellus Cobb, 1920. We report for the first-time Cephalobellus cuspidatum (Rudolphi, 1814) Leibersperger, 1960, C. osmodermae Leibersperger, 1960, and C. potosiae Leibersperger, 1960 in Hungary, all found in scarab beetle larvae. Due to incomplete original descriptions, a comprehensive redescription with detailed morphological data is presented. Additionally, an identification key for closely related Cephalobellus, Thelastoma and Severianoia species infesting scarab beetles worldwide is provided. Newly generated 18S and 28S rDNA gene sequences of C. osmodermae place it as one of the early branches within Thelastomatidae.

Hidden in the fog: morphological and molecular characterisation of Derogenes varicus sensu stricto (Trematoda, Derogenidae) from Sweden and Norway, and redescription of two poorly known Derogenes species.

Derogenes varicus (Müller, 1784) is widely reported as a trematode with exceptionally low host specificity and a wide, bipolar distribution. However, several recent studies have suggested that D. varicus represents a species complex and based on molecular evidence, four genetic lineages (labeled as "DV1-4") have been designated within the D. varicus species complex. This possibility requires improved (ideally molecular) characterisation of specimens from the type-host (Salmo salar) and type-locality (off Denmark). During examination of trematode parasites of fish from Scandinavian and Arctic waters (Sweden and Norway), we found specimens of D. varicus in the stomach of Merlangius merlangus off the coast of Sweden, and in Gadus morhua off the coast of Sweden and Norway; we compared them to D. varicus from the type-host, the Atlantic salmon Salmo salar from Norway, to verify their conspecificity. Newly generated sequences (28S rDNA, ITS2 and cox1) of Scandinavian and Arctic specimens consistent with D. varicus all formed a single clade, DV1. 28S sequences of D. varicus from S. salar from Norway, i.e., close to the Danish type locality, clustered within the DV1 clade along with sequences of D. varicus from various hosts including Limanda limanda, G. morhua and Myoxocephalus scorpius from the White Sea and the Barents Sea (Russia), without any host-related structuring. We thus consider that the lineage DV1 represents D. varicus sensu stricto. Additionally, specimens from M. merlangus had a similar morphology and anatomy to those of D. varicus from L. limanda, G. morhua and M. scorpius from T. Odhner's collection, supporting the presence of a single species in the DV1 lineage designated herein as D. varicus sensu stricto. We redescribe D. varicus sensu stricto, add new morphological characters and provide morphometric data. We infer that D. varicus types DV2-4 all relate to separate species. We also revise type-specimens of Derogenes minor Looss, 1901 from the A. Looss collection in the Swedish Museum of Natural History and provide redescriptions of it and of the type-species of the genus, Derogenes ruber Lühe, 1900. In light of their morphological distinctiveness relative to D. varicus sensu stricto, we reinstate D. parvus Szidat, 1950 and D. fuhrmanni Mola, 1912.

Title: Caché dans le brouillard : caractérisation morphologique et moléculaire de Derogenes varicus sensu stricto (Trematoda, Derogenidae) de Suède et de Norvège, et redescription de deux espèces de Derogenes peu connues. Abstract: Derogenes varicus (Müller, 1784) est largement signalé comme un trématode avec une spécificité d'hôte exceptionnellement faible et une large distribution bipolaire. Cependant, plusieurs études récentes ont suggéré que D. varicus représente un complexe d'espèces. Cette possibilité nécessite une meilleure caractérisation (idéalement moléculaire) des spécimens de l'hôte-type (Salmo salar) et de la localité-type (au large du Danemark). Lors de l'examen des trématodes parasites des poissons des eaux scandinaves et arctiques (Suède et Norvège), nous avons trouvé des spécimens de D. varicus dans l'estomac de Merlangius merlangus au large de la Suède, et dans Gadus morhua au large de la Suède et de la Norvège ; nous les avons comparés à D. varicus de l'hôte-type, le saumon atlantique Salmo salar de Norvège, pour vérifier leur conspécificité. Les séquences nouvellement générées (ADNr 28S, ITS2 et cox1) de spécimens scandinaves compatibles avec D. varicus ont toutes formé un seul clade, DV1. Les séquences 28S de D. varicus de S. salar de Norvège, c'est-à-dire proches de la localité-type au Danemark, se regroupent dans le clade DV1 avec des séquences de D. varicus de divers hôtes dont Limanda limanda, G. morhua et Myoxocephalus scorpius de la mer Blanche et la mer de Barents (Russie), sans aucune structuration liée à l'hôte. Nous considérons donc que la lignée DV1 représente D. varicus sensu stricto. De plus, les spécimens de M. merlangus avaient une morphologie et une anatomie similaires à celles de D. varicus de L. limanda, G. morhua et M. scorpius de la collection de T. Odhner, confirmant la présence d'une seule espèce dans la lignée DV1 désignée ici comme D. varicus sensu stricto. Nous redécrivons D. varicus sensu stricto, ajoutons de nouveaux caractères morphologiques et fournissons des données morphométriques. Nous en déduisons que les types DV2-4 de D. varicus se rapportent tous à des espèces distinctes. Nous révisons également les spécimens-types de Derogenes minor Looss, 1901 de la collection d'A. Looss du Muséum Suédois d'Histoire Naturelle, et fournissons des redescriptions de cette espèce et de l'espèce-type du genre, Derogenes ruber Lühe, 1900. À la lumière de leur distinction morphologique par rapport à D. varicus sensu stricto, nous rétablissons D. parvus Szidat, 1950 et Derogenes fuhrmanni Mola, 1912.

Equine Strongylidae and other parasitic nematodes described by Arthur Looss during 1895-1911 in the collections of the Swedish Museum of Natural History.

Prof. Arthur Looss (1861-1923) was a prolific German parasitologist, who, among other things, authored descriptions of 22 new species of nematodes and 115 new species of trematodes. After his death, his collection (including type material) was split between several institutions: Smithsonian National Museum of Natural History in Washington (USA), Natural History Museum in Berlin and the Natural History Museum in Leipzig (Germany), Gothenburg Museum of Natural History and Swedish Museum of Natural History (Sweden). Here we revise all type specimens of nematodes from the A. Looss collection that are currently preserved in the Swedish Museum of Natural History (Strongylus subtilis, Sclerostomum edentatum, S. vulgare, Cyathostomum labratum, C. coronatum, C. bicoronatum, C. calicatum, C. alveatum, C. catinatum, C. nassatum, C. radiatum, C. elongatum, C. auriculatum, Triodontus minor, T. serratus, C. labiatum and Uncinaria polaris), designate and describe lectotypes wherever deemed necessary and provide catalogue access numbers to all type materials. We also revise all notes and drawings associated with new species that A. Looss described and provide previously unpublished pencilled sketches and ink print-ready drawings of some of these species (Strongylus subtilis, Cyathostomum poculatum, C. radiatum, C. elongatum, C. calicatum, C. auriculatum, Triodontus serratus, Trichostrongylus vitrinus and possibly Necator africanus).

Gammarinema scyllae sp. n. and Monhystrium mangrovi sp. n. (Nematoda: Monhysteridae) from land crabs from New Caledonia.

Two new species of nematodes associated with crabs are described from New Caledonia. Gammarinema scyllae sp. n. from the gill chambers of Scylla serrata (Forsskål) is characterised by 3-4 mm long body, small outer labial and cephalic sensilla, distinct ocelli, short straight spicules and sub-cylindrical tail. Monhystrium mangrovi sp. n. from the gill chambers and body cavity of mangrove crab Neosarmatium sp. is characterised by 1-1.4 mm long body; outer labial sensilla longer than cephalic sensilla, amphid located at level with posterior stoma chamber, denticles in posterior stoma chamber and five pairs of genital papilla on tail. Phylogenetic relationships of two new species and other nematodes from the family Monhysteridae are analysed based on 18S and partial 28S rDNA sequences.

Twenty Years after De Ley and Blaxter-How Far Did We Progress in Understanding the Phylogeny of the Phylum Nematoda?

Molecular phylogenetics brought radical changes to our understanding of nematode evolution, resulting in substantial modifications to nematode classification implemented by De Ley and Blaxter and widely accepted now. Numerous phylogenetic studies were subsequently published that both improved and challenged this classification. Here we present a summary of these changes. We created cladograms that summarise phylogenetic relationships within Nematoda using phylum-wide to superfamily-wide molecular phylogenies published in since 2005, and supplemented with the phylogenetic analyses for Enoplia and Chromadoria with the aim of clarifying the position of several taxa. The results show which parts of the Nematode tree are well resolved and understood, and which parts require more research, either by adding taxa that have not been included yet (increasing taxon coverage), or by changing the phylogenetic approach (improving data quality, using different types of data or different methods of analysis). The currently used classification of the phylum Nematoda in many cases does not reflect the phylogeny and in itself requires numerous improvements and rearrangements.

Aborjinia corallicola sp. n., a new nematode species (Nematoda: Marimermithidae) associated with the bamboo coral Acanella arbuscula (Johnson).

A new species of Aborjinia Özdikmen, 2010 is described from the tissues of the cold-water bamboo coral Acanella arbuscula (Johnson) from the northwest Atlantic. Aborjinia corallicola sp. n. is characterized by 18.4-33.2 mm long body in adults; outer labial and cephalic sensilla papilliform and located 14-21 µm from anterior end, amphideal aperture located 22-41 µm from anterior end, excretory pore indistinct, rectum and anal opening functional, convex-conoid tail with broadly rounded terminus, spinneret subventral. It is placed in the genus Aborjinia based on the combination of the following characters: outer labial and cephalic sensilla papilliform in shape and located in one circle, contrary to Marimermis Rutsov & Platonova, 1974 (outer labial and cephalic sensilla setiform) and Ananus Rubtsov, 1977 and Thalassonema Ward, 1933 (outer labial and cephalic sensilla in separate circles, if known). From Aborjinia eulagiscae Tchesunov & Spiridonov, 1985 the new species differs in much shorter body, much shorter tail, presence of caudal glands and spinneret in adults, different host species. Our finding represents the first report of a nematode in a parasitic relationship with a cold-water octocoral. Phylogenetic relationships between Aborjinia and other nematodes are analyzed based on 18S rDNA sequences. Summary of all presently known species and genera of the family Marimermithidae is also given.

A draft transcriptome of a parasite Neocamacolaimus parasiticus (Camacolaimidae, Plectida).

Camacolaimidae is a clade of nematodes that include both free-living epistrate feeding forms and parasites of marine protozoans and invertebrates. Neocamacolaimus parasiticus is a parasite of marine polychaete worms. Given its phylogenetic affinities to free-living species, Neocamacolaimus can be a reference for research of the origin of parasitism in an aquatic environment. Here, we present a draft transcriptome obtained from a single post-parasitic juvenile individual of this species. The final assembly consists of 19,180 protein coding sequences (including isoforms) with the following BUSCO scores for Nematoda: 65.38% complete, 9.06% partial, and 25.56% missing, and for Metazoa: 79.45% complete, 3.17% partial, and 17.38% missing.

Uncovering diversity and metabolic spectrum of animals in dead zone sediments.

Ocean deoxygenation driven by global warming and eutrophication is a primary concern for marine life. Resistant animals may be present in dead zone sediments, however there is lack of information on their diversity and metabolism. Here we combined geochemistry, microscopy, and RNA-seq for estimating taxonomy and functionality of micrometazoans along an oxygen gradient in the largest dead zone in the world. Nematodes are metabolically active at oxygen concentrations below 1.8 µmol L-1, and their diversity and community structure are different between low oxygen areas. This is likely due to toxic hydrogen sulfide and its potential to be oxidized by oxygen or nitrate. Zooplankton resting stages dominate the metazoan community, and these populations possibly use cytochrome c oxidase as an oxygen sensor to exit dormancy. Our study sheds light on mechanisms of animal adaptation to extreme environments. These biological resources can be essential for recolonization of dead zones when oxygen conditions improve.

Descriptions of species of Acrobeles von Linstow, 1877 (Nematoda, Rhabditida, Cephalobidae) from Kelso Dunes, Mojave National Preserve, California, USA.

Populations of three rare species of the genus Acrobeles are described from the Kelso Dunes area, Mojave National Preserve, southern California. One population is identified as belonging to A. undulatus and is compared with the type population from Venezuela and one population from Iran. Males of this species are described for the first time. Another population identified as belonging to A. ornatus is compared with the type population from Colorado, USA. Specimens identified as belonging to A. dimorphus are compared with the type population from Namibia. Descriptions of the new material add morphological data important for species identification, broaden the diagnosis of Acrobeles and increase the distribution patterns of these three species.

Description of Cribronema sturhani sp. n. (Nematoda, Rhabditida, Cephalobidae), a second species of a rare genus from Cameroon.

Specimens of a population of Cribronema collected in Cameroon are described as Cribronema sturhani sp. n. The new species resembles C. cribrum, which is the only species described in the genus, but it differs from it by the following features: a somewhat shorter tail in the females, longer spermatheca and postuterine vulval sac, tail terminus in females pointed vs. harpoon-shaped, and presence vs. absence of males.

New and known species of the genus Campylaimus Cobb, 1920 (Nematoda: Araeolaimida: Diplopeltidae) from North European marine habitats.

BACKGROUND: The genus Campylaimus is a broadly distributed but relatively uncommon genus of marine and brackish nematodes with 20 nominal species and one nomen nudum. Many species descriptions and redescriptions are based on very few (single) individuals, which limits our understanding of inter- and intra-specific variability and morphology-based species boundaries. NEW INFORMATION: Two new species were found in the Skagerrak off the west coast of Sweden. Campylaimus triclados sp. n. is characterised by body 0.59-0.69 mm long; cuticle without longitudinal striation; anteriormost edge of the amphid anterior to the oral opening; dorsal limb of the amphid equal to 1.6-2.5 labial region diameters in male, 1.9 labial region diameters in female; ventral limb of the amphid extends towards anterior part of the intestine in male and midpharynx in female, 4.3-5.5 times the length of the dorsal limb in male and 2.2-2.8 times the length of the dorsal limb in female; ventral limb of the amphid is as wide as the dorsal limb; interamphideal space extends further than the posterior end of the dorsal limb but not reaching the posterior end of the ventral limb; secretory-excretory pore opens posterior to the cardia; spicules 19-24 µm long; two precloacal supplements; tail equal to 4.3-5.6 anal body diameters in length, with conoid terminal part. Campylaimus longispiculus sp. n. is characterised by body 0.56-0.65 mm long; cuticle without longitudinal striation; anteriormost edge of the amphid anterior to the oral opening; dorsal limb of the amphid equal to 1.8-2.1 labial region diameters in male; ventral limb of the amphid extends towards anterior part of the intestine in male, 2.8-3.5 times the length of the dorsal limb in male; ventral limb of the amphid is as wide as the dorsal limb; interamphideal space absent; secretory-excretory pore opens posterior to the cardia; spicules 28-35 µm long; two precloacal supplements; tail equal to 4.9-5.3 anal body diameters in length, with clavate terminal part. In addition, following nine species are new records for the fauna of Sweden: Campylaimus amphidialis, C. inaequalis, C. lefeverei, C. minutus, C. orientalis, C. rimatus, C. siwaschensis, C. striatus and C. tkatchevi.

Improved phylogenomic sampling of free-living nematodes enhances resolution of higher-level nematode phylogeny.

BACKGROUND: Nematodes are among the most diverse and abundant metazoans on Earth, but research on them has been biased toward parasitic taxa and model organisms. Free-living nematodes, particularly from the clades Enoplia and Dorylaimia, have been underrepresented in genome-scale phylogenetic analyses to date, leading to poor resolution of deep relationships within the phylum. RESULTS: We supplemented publicly available data by sequencing transcriptomes of nine free-living nematodes and two important outgroups and conducted a phylum-wide phylogenomic analysis including a total of 108 nematodes. Analysis of a dataset generated using a conservative orthology inference strategy resulted in a matrix with a high proportion of missing data and moderate to weak support for branching within and placement of Enoplia. A less conservative orthology inference approach recovered more genes and resulted in higher support for the deepest splits within Nematoda, recovering Enoplia as the sister taxon to the rest of Nematoda. Relationships within major clades were similar to those found in previously published studies based on 18S rDNA. CONCLUSIONS: Expanded transcriptome sequencing of free-living nematodes has contributed to better resolution among deep nematode lineages, though the dataset is still strongly biased toward parasites. Inclusion of more free-living nematodes in future phylogenomic analyses will allow a clearer understanding of many interesting aspects of nematode evolution, such as morphological and molecular adaptations to parasitism and whether nematodes originated in a marine or terrestrial environment.

Description of Drilocephalobus moldavicus Lisetskaya, 1968 (Rhabditida: Osstellidae) from Kelso Dunes, Mojave National Preserve, California, USA.

Specimens of Drilocephalobus moldavicus are described from the Kelso Dunes area, Mojave National Preserve, southern California. This is the first record of the genus in North America. The specimens of this population are characterized by a body length of 322-417 µm in females and 403 µm in the male; cuticle finely annulated; lateral field with five incisures, extending to phasmid and two incisures extending almost to tail terminus in both sexes; lip region helmet-shaped, offset from body contour; lips amalgamated; stoma with thin walls lacking sclerotizations; pharynx without distinct divisions, cylindrical, widening slightly at about 1/3 of its length and basally, without valves; spermatheca 14-19 µm long; postvulval uterine sac 25-27 µm long; spicules 23 µm long; and female tail conoid-elongate with rounded terminus.

Taxonomy assignment approach determines the efficiency of identification of OTUs in marine nematodes.

Precision and reliability of barcode-based biodiversity assessment can be affected at several steps during acquisition and analysis of data. Identification of operational taxonomic units (OTUs) is one of the crucial steps in the process and can be accomplished using several different approaches, namely, alignment-based, probabilistic, tree-based and phylogeny-based. The number of identified sequences in the reference databases affects the precision of identification. This paper compares the identification of marine nematode OTUs using alignment-based, tree-based and phylogeny-based approaches. Because the nematode reference dataset is limited in its taxonomic scope, OTUs can only be assigned to higher taxonomic categories, families. The phylogeny-based approach using the evolutionary placement algorithm provided the largest number of positively assigned OTUs and was least affected by erroneous sequences and limitations of reference data, compared to alignment-based and tree-based approaches.

The Swedish marine nematologist Carl Allgén (1886-1960): a bio-bibliography and his collection.

The Swedish marine nematologist Carl Allgén (1886-1960) published 185 scientific papers on parasitic, terrestrial, limnic and especially marine nematodes between 1921 and 1960. Among them are also some papers on species of suctorians found mostly on desmodorid nematodes. He described about 70 new genera and over 800 new species and subspecies of nematodes. Allgén left a large collection of nematodes to the Swedish Museum of Natural History in Stockholm and it is now deposited in the invertebrate collection of the Zoology department. The collection comprises about 4500 slides in total, with about 310 slides containing type specimens collected from the Arctic to Antarctica. Allgén's publications have to a large extent been ignored by scientists working on marine nematodes, likely because of the poor quality of many of his species descriptions. The authors want to remind the scientific community about the existence of Allgén's collection, its availability for study and its importance for nematode taxonomy and systematics. A complete list of Allgén's publications, a list of all species described by him, and a list of type material available is presented.

Metabarcoding of marine nematodes - evaluation of reference datasets used in tree-based taxonomy assignment approach.

BACKGROUND: Metabarcoding is becoming a common tool used to assess and compare diversity of organisms in environmental samples. Identification of OTUs is one of the critical steps in the process and several taxonomy assignment methods were proposed to accomplish this task. This publication evaluates the quality of reference datasets, alongside with several alignment and phylogeny inference methods used in one of the taxonomy assignment methods, called tree-based approach. This approach assigns anonymous OTUs to taxonomic categories based on relative placements of OTUs and reference sequences on the cladogram and support that these placements receive. NEW INFORMATION: In tree-based taxonomy assignment approach, reliable identification of anonymous OTUs is based on their placement in monophyletic and highly supported clades together with identified reference taxa. Therefore, it requires high quality reference dataset to be used. Resolution of phylogenetic trees is strongly affected by the presence of erroneous sequences as well as alignment and phylogeny inference methods used in the process. Two preparation steps are essential for the successful application of tree-based taxonomy assignment approach. Curated collections of genetic information do include erroneous sequences. These sequences have detrimental effect on the resolution of cladograms used in tree-based approach. They must be identified and excluded from the reference dataset beforehand.Various combinations of multiple sequence alignment and phylogeny inference methods provide cladograms with different topology and bootstrap support. These combinations of methods need to be tested in order to determine the one that gives highest resolution for the particular reference dataset.Completing the above mentioned preparation steps is expected to decrease the number of unassigned OTUs and thus improve the results of the tree-based taxonomy assignment approach.

Metabarcoding of marine nematodes - evaluation of similarity scores used in alignment-based taxonomy assignment approach.

BACKGROUND: The diversity of organisms is being commonly accessed using metabarcoding of environmental samples. Reliable identification of barcodes is one of the critical steps in the process and several taxonomy assignment methods were proposed to accomplish this task, including alignment-based approach that uses Basic Local Alignment Search Tool (BLAST) algorithm. This publication evaluates the variability of 5' end of 18S rRNA barcoding region as expressed by similarity scores (alignment score and identity score) produced by BLAST, and its impact on barcode identification to family-level taxonomic categories. NEW INFORMATION: In alignment-based taxonomy assignment approach, reliable identification of anonymous OTUs to supraspecific taxa depends on the correct application of similarity thresholds. Since various taxa show different level of genetic variation, practical application of alignment-based approach requires the determination and use of taxon-specific similarity thresholds.

Alloionema similis n. sp., a genetically divergent sibling species of A. appendiculatum Schneider, 1859 (Rhabditida: Alloionematidae) from invasive slugs in California, USA.

A new species of Alloionema Schneider, 1859, A. similis n. sp., and the known species A. appendiculatum Schneider, 1859 were isolated from cadavers of invasive slugs in California. Both species are described based on morphology, morphometrics and molecular data. Alloionema similis n. sp. is morphologically very similar to A. appendiculatum but can be distinguished by a more posterior position of the excretory pore in the Kleinform females and longer tail in the Kleinform males. Substantial differences between the two species are, however, found in both 18S and 28S rDNA sequences. Sequence analysis revealed unambiguous autapomorphies in nucleotide sequence and secondary structure of rRNA genes, separating A. appendiculatum and A. similis n. sp. Molecular phylogenies were inferred from concatenated secondary-structure based multiple sequence alignments of nearly complete 18S and the D1-D3 domains of the 28S rRNA genes. Phylogenetic analyses placed these two species as sister taxa in a monophyletic clade, separately from Neoalloionema tricaudatum Ivanova, Pham Van Luc & Spiridonov, 2016 and N. indicum Nermut, Puza & Mrácek, 2016.

Corrigendum: Nematodes from terrestrial and freshwater habitats in the Arctic.

[This corrects the article DOI: 10.3897/bdj.2.e1165.].