Abstract

The taxonomic impediment in nematology is expanding rather than receding: in the past decade estimates of nematode species richness have increased by several orders of magnitude, while the number of active nematode taxonomists has continued to decline steadily. In order to survive as a discipline in the new century, nematode taxonomy will therefore have to i) prioritise taxa that are relevant to other scientific investigations, ii) provide identification and classification tools that are easily applicable by nonspecialists, and iii) focus on revealing patterns of relatedness rather than on compiling exhaustive catalogues of species, since the latter will never remotely reach completion. Traditional morphological studies based on light microscopy do not meet these needs because they provide insufficient character resolution and require too much specialist knowledge. Phylogenetic approaches are more promising, especially when incorporating molecular sequence data as well as other non-traditional character suites. En nématologie, les obstacles taxinomiques sont en accroissement plutôt qu’en recul: pendant la dernière décennie, les estimations relative à la diversité en espèces ont été accrues par plusieurs ordre de grandeur tandis que le nombre de taxinomistes a continué à décroître régulièrement. Pour se maintenir en tant que discipline au cours du nouveau siècle, la taxinomie nématologique devra donc i) donner priorité à des taxons en relation directe avec d’autres recherches scientifiques, ii) produire des instruments d’identification et de classification plus accessibles aux non-spécialistes, et iii) se concentrer sur la découverte de relations d’affinité plutôt que sur la compilation de catalogues d’espèces lesquels n’atteindront jamais l’exhaustivité. Les études morphologiques traditionnelles basées sur la microscopie optique ne peuvent répondre à ces besoins du fait qu’elles n’ont pas une résolution suffisante pour les caractères et qu’elles requièrent trop de connaissances spécialisées. Les approches phylogénétiques sont plus prometteuses, spécialement lorsqu’elles sont basées sur des séquences moléculaires et d’autres séries de caractères non-traditionnels.

In: Nematology

Abstract

The parasitic Nematoda have traditionally been classified distinct from free-living species, and animal parasites treated separately from plant parasites. In classical concepts of phylogenetic relationships within the phylum, parasitic groups are usually afforded ordinal status and their origins are often obscure. We have been using molecular phylogenetics to examine the interrelationships of animal parasites with free-living and plant-parasitic groups, and find that a new view of the origins and radiation of animal parasites is warranted. Using sequence from the nuclear small subunit ribosomal RNA gene, we have constructed an alignment that allows robust phylogenetic inference. With this dataset, we place the Strongylida as a monophyletic clade nested within the Rhabditina. The Ascaridida, Oxyurida and Spirurida are closely related, but currently have no clear closest free-living sister taxon. Strongyloides spp. are rooted in a radiation of cephalobid/tylenchid species. Where available, other sequences in general confirm these relationships. Les Nematoda parasites ont été traditionnellement classifiés séparément des espèces libres, les parasites d’animaux étant traités séparément des parasites de plantes. Suivant les concepts classiques des relations phylogénétiques à l’intérieur du phylum, les groupes parasites sont habituellement traités au niveau ordinal et leurs origines sont souvent inconnues. Utilisant la phylogénie moléculaire, les interrelations des parasites animaux avec les groupes d’espèces libres et parasites de plantes ont été étudiées conduisant à la conclusion qu’une nouvelle approche des origines et de l’évolution des parasites animaux est nécessaire. Sur la base de la petite sous-unité nucléaire du gène de l’ARN ribosomal, un alignement est proposé qui permet une inférence phylogénétique solide. Avec cet ensemble de données, les Strongylida sont considérés comme un clade monophylétique emboîté au sein des Rhabditina. Les Ascaridida, Oxyurida et Spirurida sont étroitement reliés, mais jusqu’à présent sans relation étroite claire avec des taxons de nématode libre. Les Strongyloides spp. ont évolué à partir des cephalobides/tylenchides. Lorsqu’elles sont disponibles, les données issues d’autres séquences confirment le plus souvent ces relations.

In: Nematology

Abstract

An unusual new ceramonematid, Ceramonema nasobema sp. n., is described using light and scanning electron microscopy. It is particularly characterised by the presence of a perioral tube projecting 5.5-7.0 μm anterior to the lips, moderately long body (0.86-1.09 mm), relatively small number of body annules (121-134), weakly developed zygapophyses, absence of intracuticular vacuoles, pronounced sexual dimorphism in amphid shape with the male ventral amphidial branch extending as far posterior as the 55-80th annule (no extension in females), barrel-shaped stoma, sigmoid and anteriorly inclined vagina without sclerotisations, gubernaculum with dorsal apophyses and relatively uniform cloacal annules. The new species differs from all other known species of Ceramonema especially by the shape of the amphid in males, the strongly projecting perioral tube and the inclined, sigmoid, vagina. Additional data on morphology of Ceramonema algoensis (from Natal Bay, South Africa) are also provided as this species has the most prominent perioral tube among previously described members of the genus.

In: Nematology

Longidorus mindanaoensis n. sp. is described from samples associated with riverine mangroves in the Philippines and is the first Longidorus species collected from such a habitat. Its relationship within the genus is inferred from molecular and morphological data. Phylogenetic inferences were performed for D2-D3 and SSU rDNA using appropriate phylogenetic algorithms. The new species is characterised by a thickened basal layer of the body cuticle with prominent spiral fibres, a dome-shaped continuous lip region, an oval to elliptical fovea with pore-like opening, the guiding ring at 2.2-2.5 lip region diam. from the anterior end, very weakly developed odontophore, all three pharyngeal gland nuclei at about the mid-point of the basal bulb, vulva at 30-39%, tail convex-conoid to hemispherical, shorter than anal body diam., males with 19-24 ventromedian supplements, and four juvenile stages, all with the replacement odontostyle at a short distance from the functional one. On the basis of amphid shape and structure, shape of anterior body region and general body shape, L. mindanaoensis n. sp. comes close to L. caespiticola, L. eridanicus, L. helveticus, L. macrosoma, L. poessneckensis, L. orongorongensis, L. waikouaitii and L. belondiroides. D2-D3 analysis placed the new species as sister to L. pisi and the two combined are sister clade to a monophyletic group that includes (L. poessneckensis (L. caespiticola (L. helveticus, L. macrosoma))). However, on the basis of SSU phylogeny, L. mindanaoensis n. sp. is positioned within a clade that includes (Longidorus sp. (L. mindanaoensis n. sp. (L. poessneckensis (L. helveticus, L. macrosoma)))). The ‘close’ relationship of the new species with L. pisi in the D2-D3 tree is incongruent with the widely different morphology of the two species. The other species that are close to the new species in the cladogram are in agreement with the morphology.

In: Nematology

Phasmarhabditis hermaphrodita is reported for the first time in North America from cadavers of the invasive slug species Deroceras reticulatum, D. laeve and Lehmannia valentiana collected from three different locations in California, USA. Four isolates were identified using combined morphology, morphometrics and molecular sequence data for complete internal transcribed spacer (ITS-1, 5.8S, ITS-2), D2-D3 expansion segments of the large subunit (LSU or 28S) and nearly complete small subunit (SSU or 18S) ribosomal DNA. Extremely low sequence variations in the COI gene of the mitochondria were observed among US isolates as well as between US isolates and the two UK sequences. The occurrence of P. hermaphrodita in North America has regulatory implications for potential biological control strategies against non-native gastropod species that are pests in ornamental and agricultural cultivation on this continent. The D2-D3 sequence of the LSU rDNA is new for the species.

In: Nematology

Abstract

Acromoldavicus (Cephalobina, Cephaloboidea) with its highly distinctive lip region has only a single species, Acromoldavicus skrjabini Nesterov & Lisetskaya, originally described from Moldova and subsequently also detected at sites in the Middle East and near the Mediterranean. Herein, Acromoldavicus mojavicus n. sp. is described from sandy soil surrounding a Joshua tree (Yucca brevifolia) in a remote area of the Mojave Desert, California, USA. The lip region of A. mojavicus n. sp. is bilaterally symmetrical with three triangular probolae surrounded by three pairs of plate-like lips. The lip region is organised along similar lines as that of A. skrjabini, but differs in several respects, such as its larger size, presence of elongate posterior processes on each lip and division of the lateral lips into two lobes (excluding the dorso-sublateral guard processes). In addition, phylogenetic interpretation of sequence data from the large-subunit of ribosomal DNA provides further evidence for autapomorphies and separate species status for A. skrjabini and A. mojavicus n. sp. Characteristics shared with Cephaloboidea include the offset spermatheca and males with eight pairs of genital papillae. Both species of Acromoldavicus have a buccal capsule with a reduced gymnostom, a character that seems to be shared with the cephalobid Elaphonema and in part is a basis for placement of both genera in Elaphonematidae. The species A. mojavicus n. sp. exhibits additional similarities with Elaphonema spp. that further support this placement.

In: Nematology

Abstract

A detailed morphological description (light and scanning electron microscope observations) is given of two isolates currently used in molecular and developmental studies: PDL0024, Panagrobelus stammeri Rühm, 1956 and PDL0025, a new species herein described as Plectonchus hunti n. sp. We redescribe the lip region, interpret the orientation of the lips in P.stammeri and provide additional morphological and morphometric diagnostic features. Plectonchus hunti n. sp. is characterised by the bifurcating spicule tip and by the placement of the male genital papillae in a 3/3 + p + 2 arrangement. Additionally, females of this new species can be differentiated from other species of Plectonchus by the more anterior position of the vulva, the more anterior location of the excretory pore and the tail morphology. An emended diagnosis for this genus is provided. In this study we demonstrate that both studied taxa share morphological similarities, such as the presence of a 'cephaloboid-type' spermatheca. Our observations also indicate slight but consistent differences in cell composition of the female reproductive system between these two taxa.

In: Nematology

Abstract

Measurements, line drawings and scanning electromicrographs are provided of Baujardia mirabilis gen. n., sp. n., isolated from pitcher fluid of Nepenthes mirabilis from Thailand. The new genus differs from all known nematodes in having two opposing and offset spermatheca-like pouches at the junction of oviduct and uterus. It also differs from most known Rhabditida in having four cephalic setae instead of papillae. Phylogenetic analysis of small subunit rDNA sequence data robustly places the new genus within Panagrolaimidae as a sister taxon to Panagrellus. These unusual nematodes resemble Panagrellus in body size (1.8-2.7 mm in females, 1.3-1.9 mm in males) and in the monodelphic, prodelphic female reproductive system with thickened vaginal walls and prominent postvulval sac. However, they differ from Panagrellus in the characters mentioned above, in their comparatively longer stegostom and in the shape of the male spicules. Because of its aberrant characters, inclusion of this new genus in Panagrolaimidae requires changes to the family diagnosis.

In: Nematology

Abstract

Hirschmanniella santarosae sp. n. is described from the largest vernal pool in the Santa Rosa Plateau Ecological Reserve, Murrieta, California, USA. The cryptic new species is morphologically very close to H. pomponiensis and H. gracilis as it can be distinguished from the former only by a more anterior excretory pore position and by more flattened as well as laterally expanded stylet knobs, whilst it differs from the latter in the greater distance from phasmid to tail tip and in the bursal alae ending near the phasmids rather than near the tail tip. Analysis of the rDNA small subunit (SSU) and D2D3 expansion segments of the large subunit (LSU) shows that H. santarosae sp. n. is genetically distinct, having respective sequence homology of 98.89% and 95.9% with H. pomponiensis for these loci. Congruence in SSU and D2D3 gene trees as well as unambiguous character autapomorphies further support the new species status of H. santarosae sp. n. and sibling relationship with H. pomponiensis. Although many more isolates and species will need to be studied before informative biogeographic analyses can be performed, the presently available sequence data suggest that some Hirschmanniella lineages have diversified independently on either side of the Atlantic.

In: Nematology

Abstract

Carcharolaimus ramirezi was found in six soil samples from four islands of the Galápagos Archipelago. It is described for the first time since its original discovery, with particular emphasis on the morphology of its anterior end as seen under light microscope and SEM. Six large, but thin, liplets overhang the labial basket, which consists of thick plates ornamented with irregular ridges and denticles. Posterior to the labial basket, six pillars form a postlabial cage and provide attachment for eight dilatatores buccae. The species can survive desiccation and is probably well adapted to arid soils. Paratypes of C. bediensis were also studied and revealed that this species is actually synonymous with C. banaticus, rather than being very close to C. ramirezi as suggested by previous descriptions. The recently proposed genus Carcharodiscus is rejected, and the possible synonymy of Carcharolaimus with the senior genus Antholaimus is noted. A compendium to the genus Carcharolaimus is provided.

In: Nematology