Morphology and ultrastructure of the bacterial receptacle in Steinernema nematodes (Nematoda: Steinernematidae)

Infective juveniles of entomopathogenic nematodes in the genus Steinernema harbor symbiotic bacteria, Xenorhabdus spp., in a discrete structure located in the anterior portion of the intestine known as the 'bacterial receptacle' (formerly known as the bacterial or intestinal vesicle). The receptacle itself is a structured environment in which the bacteria are spatially restricted. Inside this receptacle, bacterial symbionts are protected from the environment and grow to fill the receptacle. Until now, no comparative study across different Steinernema spp. has been undertaken to investigate if morphological variation in this structure exists at the interspecific level. In this study, we examined the bacterial receptacles of 25 Steinernema spp. representatives of the currently accepted five evolutionary clades. Our observations confirmed the bacterial receptacle is a modification of the two most anterior cells of the ventricular portion of the intestine. Size of the bacterial receptacle varied across the examined species. Steinernema monticolum (clade II) had the largest receptacle of all examined species (average: 46×17 μm) and S. rarum (no clade affiliation) was noted as the species with the smallest observed receptacle (average: 8×5 μm). At the morphological level, species can be grouped into two categories based on the presence or absence of vesicle within the receptacle. The receptacles of all examined species harbored an intravesicular structure (IVS) with variable morphology. All examined taxa members of the 'feltiae' (clade III) and 'intermedium' (clade II) clades were characterized by having a vesicle. This structure was also observed in S. diaprepesi (clade V), S. riobrave (clade IV) and S. monticolum (clade I).     

Embryology and Life Cycle of Tylenchorhynchus claytoni Steiner, 1937 (Nematoda: Tylenchoidea)

Development of Tylenchorhynchus claytoni from unsegmented egg to hatching takes 135 hr at 22-25 C. The fourth molt lasts 5 to 6 days. During exsheathment the cast cuticle of the larva separated into two unequal parts, breaking near either the anterior or posterior end. The life cycle from egg to egg required from 31 to 38 days at 28 C on alfalfa seedlings and included four molts and four larval stages. Sexual differentiation was apparent in third-stage larvae.     

Pasteuria endospores from Heterodera cajani (Nematoda: Heteroderidae) exhibit inverted attachment and altered germination in cross-infection studies with Globodera pallida (Nematoda: Heteroderidae)

The Pasteuria group of Gram-positive, endospore-forming bacteria are parasites of invertebrates and exhibit differences in host specificity. We describe a cross-infection study between an isolate of Pasteuria from pigeon pea cyst nematode, Heterodera cajani, which also infects the potato cyst nematode, Globodera pallida, from the United Kingdom. A proportion of the attached endospores, 13% on H.?cajani and 22% on G.?pallida adhere to the cuticle in an inverted orientation. Inverted and conventionally attached endospores germinated and produced bacillus-like rods that completed their life cycle in 相似文献   

Morphology and Ultrastructure of the Intestine in a Plant-Parasitic Nematode,Tylenchorhynchus dubius

An unusual feature of the intestine in Tylenchorhynchus dubius is the presence, within the intestinal cytoplasm, of an extensive system of fibrillar bundles consisting of thin (14 nm diam) filaments and thick (70-90 nm diam), rod-like elements arranged in closely packed arrays. The larger of the fibrillar bundles, for which the term "intestinal fasciculi" is proposed, are evident in whole mounts and apparently correspond to the lateral or sinuous canals described in some other tylenchids. The nature and function of fasciculi are not known, but some possibilities are considered. Fasciculi were found in at least seven other species of Tylenchorhynchus. The intestinal cytoplasm also contains the usual sub cellular organelles and large amounts of reserve materials in the form of particulate glycogen and three types of globules. The surface of the cells bordering the lumen is elaborated into numerous microvilli which have central filaments and often bear regular external projections. Although terminal bars delimit the apical margins between cells, the frequent lack of complete lateral boundaries and extensive length of the fasciculi indicate that the intestinal epithelium is a multinucleate mosaic or syncytium.     

Morphology,ultrastructure, and development of the parasitic larva and its surrounding trophamnion of Polypodium hydriforme Ussov (Coelenterata)

Summary The larval stage of Polypodium hydriforme is planuliform and parasitic inside the growing oocytes of acipenserid fishes. The larva has inverted germ layers and a special envelope, the trophamnion, surrounding it within the host oocyte. The trophamnion is a giant unicellular provisory structure derived from the second polar body and performing both protective and digestive functions, clearly a result of adaptation to parasitism. The trophamnion displays microvilli on its inner surface, and irregular protrusions anchoring it to the yolk on its outer surface. Its cytoplasm contains long nuclear fragments, ribosomes, mitochondria, microtubules, microfilaments, prominent Golgi bodies, primary lysosomes, and secondary lysosomes with partially digested inclusions.The cells of the larva proper are poorly differentiated. No muscular, glandular, neural, interstitial, or nematocyst-forming cells have been found. The entodermal (outer layer) cells bear flagella and contain rough endoplasmic reticulum; the ectodermal (inner layer) cells lack cilia and contain an apical layer of acid mucopolysaccharid granules. The cells of both layers contain mitochondria, microtubules, and Golgi bodies; their nuclei display large nucleoli with nucleolonema-like structure, decondensed chromatin, and some perichromatin granules. At their apical rims, the ectodermal cells form septate junctions; laterally, the cells of both layers form simple contacts and occasional interdigitations. The lateral surfaces of entodermal cells are strengthened by microtubules.     

Morphology and ultrastructure of the pharynx in Solenofilomorphidae (Acoela)

The homology of pharynges within the mostly pharynx-less Acoela has been a matter of discussion for decades. Here, we analyze the pharynges of three members of the Solenofilomorphidae, Myopea sp. and two species of the genus Solenofilomorpha, by means of light and transmission electron microscopy. Special focus is placed on the ultrastructure of the pharyngeal musculature, epidermis surrounding the mouth, pharyngeal epithelium, and junction with the digestive parenchyma. The main goal of this study was to evaluate the usefulness of certain characters for broader comparisons within the Acoela. Among the three species, characters relating to position of the mouth, presence and elaboration of sphincter muscles, presence of pharyngeal glands, and ultrastructure of epitheliosomes proved to be variously species- and genus-specific. The arrangement of pharyngeal muscles and their connection with body wall musculature, ultrastructure of receptor cells, and morphology of a nonciliated glandular region in the posterior pharynx, in contrast, appear to be characteristic of the family Solenofilomorphidae and thus of predominant interest for comparisons with other acoel families.     

The Morphology of Thynnascaris adunca (Rudolphi) (Nematoda, Ascaridoidea)

The following body parts of the fish nematode Thynnascaris adunca were studied by using SEM and TEM: anterior and posterior ends, digestive tract, particularly the oesophagus and its glandular tissue, male and female reproductive organs, excretory and nervous systems, and body wall. The ova in the uterus of a female studied by SEM were found to contain II-stage larvae: this is at variance with previous reports. Contrary to accepted views, each body wall muscle was found to have more than one process ("arm") reaching the dorsal/ventral nerve.     

Morphology and ultrastructure of Devonian prasinophycean algae (Chlorophyta)

The ultrastructure of three Devonian prasinophycean species (green algae): Inderites reticulatus (Naumova) Telnova, I. devonicus (Naumova) Telnova, and Tasmanites domanicus (Naumova) Telnova is described. Members of the genus Inderites are shown to have double-layer walls (outer homogeneous layer, and inner finely porous layer). The genus Tasmanites is characterized by single-layer (homogeneous) walls. All of the described Paleozoic Tasmanites have a similar ultrastructure. Species differ in shell thickness and distributional pattern of pores.     

Parthenogenesis in the parasitic and free-living forms of Strongyloides papillosus (Nematoda,Rhabdiasoidea)

Both parasitic and free-living females of a calf strain of Strongyloides papillosus have a chromosome number of 2n=4. Both forms reproduce by diploid parthenogenesis. Oocytes of parasitic females undergo only one homeotypic maturation division without homologous chromosome pairing (mitotic parthenogenesis). Oocytes of free-living females show normal pairing and disjunction of the homologous chromosomes, but only one diploid polar body is expelled (meiotic parthenogenesis). Reconstitution of the diploid chromosome number occurs by separation of the two sister chromatids of each univalent during or after anaphase I.This investigation was supported by the Consiglio Nazionale delle Ricerche (C.N.R.) of Italy.     

A Key and Diagnostic Compendium to the Species of the Genus Tylenchorhynchus Cobb, 1913 (Nematoda: Belonolaimidae)

An identification key to 111 species of Tylenchorhynchus is given. Tylenchorhynchus is defined as containing only those species with four incisures in the lateral field. A compendium providing the most important diagnostic characters for use in identification of species is included as a supplement to the key. Some species in a related but unnecessary genus were placed in the genus Tylenchorhynchus, based on morphological structures and logical groupings of the species. Bitylenchus iphilus is transferred to Tylenchorhynchus. The diagnosis of Tylenchorhynchus is emended, and a list of all the valid species of the genus is given. The characters most useful for separating species are the stylet length, shape of lip region, number of lip annules, shape of tail and tail terminus, number of tail annules, and position of vulva (V%). As defined in the paper, the genus currently is composed of 111 valid species.     

Morphology and ultrastructure of the gut in Spadella cephaloptera (chaetognatha)

Structural and ultrastructural studies on the gut of the chaetognath Spadella cephaloptera, as well as observations on the feeding behavior of specimens bred in the laboratory, were conducted. The gut displays four distinct zones: pharynx, esophagus, and intestine, to which are connected a pair of diverticula, and the rectum, differing in length, shape, and cellular composition. The intestine alone represents ∼90% of the gut length. Upon ingestion, food in the intestine is submitted to successive backward and forward peristaltic movements until digestion has ended. Ultrastructural observations have identified five distinct cell types from granule morphology and the presence or absence of cilia at the apex of the cells. Three of the types undoubtedly correspond to secretory cells. They are the (1) pharyngeal, (2) esophageal, and (3) light intestinal ciliated cells, which could be, respectively, implicated in (1) mucous, (2) enzyme, and (3) both mucous and enzyme secretions. The fourth type, which corresponds to dense intestinal ciliated cells, displays all the characteristics of cells specialized in the absorption of macromolecules and intracellular digestion. The products of this digestion could be temporarily stored inside dense granules before being utilized during vitellogenesis. Except for the presence of cilia, the fifth type, which is localized in the short rectum, represents a common polyhedral epithelial cell type. © 1996 Wiley-Liss, Inc.     

Morphological and molecular characteristics of a new species of Pasteuria parasitic on Meloidogyne ardenensis

A species of the hyper-parasitic bacterium Pasteuria was isolated from the root-knot nematode Meloidogyne ardenensis infecting the roots of ash (Fraxinus excelsior). It is morphologically different from some other Pasteuria pathogens of nematodes in that the spores lack a basal ring on the ventral side of the spore and have a unique clumping nature. Transmission electron microscopy (TEM) showed that the clumps of spores are not random aggregates but result from the disintegration of the suicide cells of the thalli. Sporulation within each vegetative mycelium was shown to be asynchronous. In addition to the novel morphological features 16S rRNA sequence analysis showed this to be a new species of Pasteuria which we have called P. hartismeri. Spores of P. hartismeri attach to juveniles of root-knot nematodes infecting a wide range of plants such as mint (Meloidogyne hapla), rye grass (unidentified Meloidogyne sp.) and potato (Meloidogyne fallax).     

Morphology and ultrastructure of orbicules in the subfamily Ixoroideae (Rubiaceae)

Orbicules were studied in 43 species belonging to 32 genera of the five tribes of the Ixoroideae (Rubiaceae). The orbicules were investigated with scanning electron microscopy (SEM), light microscopy (LM), and transmission electron microscopy (TEM). Orbicules are present in all species investigated of the tribes Pavetteae, Octotropideae and Coffeeae. In the tribes Gardenieae and Aulacocalyceae orbicules were found in some species, while they were absent in others. 15 species out of 11 genera lack orbicules. Three orbicule types (III, V, and VI) could be distinguished, mainly on the basis of general morphological and ultrastructural variations. Orbicules that belong to type III (0.50-1.29μm) have perforations in their wall, a regular or irregular shape and two or three electron transparent cores. This orbicule type, exclusively found in all Pavetteae species investigated, can be divided into two subtypes. Orbicules of subtype IIIa are present in all genera related to Ixora, and orbicules of subtype IIIb in those genera related to Tarenna. Orbicules of type V (0.97-1.86μm) are present in Himalrandia tetrasperma (Aulacocalyceae), and in all Octotropideae genera investigated, except Feretia. Complexes of more than three individual orbicules characterize this type. They are irregularly shaped and have many perforations as well as sporopollenin granules on the orbicule wall. In all species investigated of tribe Coffeeae, type VI orbicules (0.56-1.60μm) are present. These orbicules are characterized by their embedded position towards the tapetal membrane, their aggregated form and by the presence of perforations as well as sporopollenin granules on their orbicule wall. In the tribe Gardenieae different types of orbicule were found (V, VI and orbicules that cannot be classified in our typology). Our results suggest that orbicule characters in the Ixoroideae may be systematically useful on tribal level.     

The ultrastructure of the cuticle of adult female Mermis nigrescens (Nematoda)

The ultrastructure of the cuticle of the adult female nematode Mermis nigrescens has been described. There is an epicuticle and three-layered membrane covering the cuticle. The cortex is penetrated by canals which extend from the surface of the cuticle to the matrix of the layer beneath the cortex. Beneath the cortex are two layers of giant fibres which spiral around the nematode, a thick layer containing a network of fibres and a basal layer containing a vacuolated matrix material. it is thought that the epicuticle is secreted from the canals in the cortex. The possible functions of the layers in the cuticle have been discussed and similarities with the cuticle of the Acanthocephala have been noted.     

Morphology and ultrastructure of Mammillaria gracillis (Cactaceae) in in vitro culture

Morphogenetic status of cactus Mammillaria gracillis Pfeiff. tissue culture was studied by light and electron microscopy. In vitro propagated shoots spontaneously developed callus. This callus regenerated normal and hyperhydric shoots without exogenous hormones. Tumour tissue induced by wild or rooty strains of Agrobacterium tumefaciens never expressed any morphogenetic potential. Light microscopy showed cellular characteristics of morphologically different tissues. Ultrastructural studies revealed changes in plastids: secondary dedifferentiation of mature chloroplasts, thylakoid swelling and disruption, phytoferritin accumulation, plastid elongation and increase in size. Changes in chlorophyll and carotenoid content were in accordance with degradation of the thylakoid system. Plastids were confirmed as very sensitive organelles to an artificial hyperhydric environment as well as to Agrobacteria-mediated cell transformation.     

The morphology and differential diagnosis of parasitic larvae of Triodontophorus (Nematoda, Strongylidae)

356 parasitic larvae of the genus Triodontophorus from Equidae (two Equus hemionus and one E. grevyi) have been investigated. They belong to three phenons, which differ from each other by the shape and dimensions of a stoma, the structure of teeth and other signs. That phenons belong to three different species: T. serratus, T. tenuicollis and T. brevicauda. The differential diagnosis of L4 of that species of Triodontophorus are given.