Ultrastructure of the pharynx of Prorhynchus (Platyhelminthes, Lecithoepitheliata)

The pharynx variabilis of Prorhynchus is strongly muscular, with a small pharyngeal fold and a thin surrounding sheath. There is one row of inner longitudinal musclcs, up to six rows of inner circular muscles, many radial muscles, one row of outer circular and one row of outer longitudinal muscles, with no sphincter muscle groups. Three kinds of secretion, produced in a cluster of gland cell bodies posterior to the pharynx, enter the pharynx wall. They travel anteriorly in ducts and two kinds unite in a common duct just prior to discharging into the anterior region of the pharynx lumen. The perikarya of lumen epithelial cells lie within the pharynx musculature and, at the anterior and posterior margins of the pharynx, external to the pharynx. Bundles of ciliated receptors are numerous at the anterior and posterior constrictions. Similarities in the ultrastructure of flame bulbs of Rhabdocoela and Lecithoepitheliata suggest a relationship between these groups. However, the usefulness of pharynx ultrastructure for platyhelminth phylogeny cannot be assessed until complete ultrastructural studies of various groups of Rhabdocoela have been made.     

Ultrastructure of Gonionchus australis (Xyalidae,Nematoda)

Observations are reported on the ultrastructure of the buccal cavity, body cuticle, spermatids, spermatozoa, male genitalia, and caudal glands of Gonionchus australis. The buccal cuticle is a continuation of the pharyngeal cuticle. Anteriorly it is secreted by arcade tissue and overlaps the mouth rim; laterally it forms longitudinal tooth ridges. The non-annulated cephalic cuticle differs sharply from the remainder of the body wall cuticle. The cortical and basal zones become much thinner, while a largely structureless, lucent median zone expands to fill the bulk of the lips and lip flaps. Spermatids possess fibrous bodies, multimembrane organelles, mitochondria, and compact chromatin. The spermatozoa of G. australis resemble those of most other nematodes by the absence of the nuclear envelope and presence of fibrous bodies, mitochondria, and compact chromafin. The ejaculatory duct possesses microvilli. Two ejaculatory glands lie beside the duct. Two neurons are located within each spicule and each part of the paired gubernaculum. Caudal gland nuclei are large, with dispersed chromatin. The ducts of all three caudal glands are filled with secretory vesicles.     

The ultrastructure of the cuticle of Nematoda. II. The cephalic cuticle of Stilbonematinae (Adenophorea,Desmodoridae)

Summary  The ultrastructure of the cephalic cuticle of 6 of 7 representative genera of Stilbonematinae (Eubostrichus, Catanema, Laxus, Robbea, Leptonemella, Stilbonema) is investigated using SEM and TEM techniques. Additionally, one species of Spirinia (Spiriniinae) and one of Desmodora (Desmodorinae) were studied for outgroup comparison. Most of the studied species show modifications of the cephalic cuticle. Furthermore, at least four different pathways have been developed to reinforce the head within Stilbonematinae. Species with a coarsely annulated somatic cuticle (Leptonemella sp., Stilbonema majum, and Desmodora ovigera) developed a rigid, non-annulated cephalic capsule by modifying the main constructing element of the median zone, the ’’ring body.’’ In faintly annulated Laxus oneistus, the annulated cephalic capsule results from a newly inserted ’’block layer’’ between the median and basal zone. The non-annulated cephalic capsule of Robbea sp. is formed by both the block layer and the ring body element. The annulated capsule of Catanema sp. stems from a doubled number of fiber layers within the basal zone. In Spirinia sp., only the amphidial region is strengthened in what could be termed an amphidial shield. All forms with cephalic capsules show mechanisms to keep the oral region pliable. Only Eubostrichus topiarius lacks a reinforcement of the cephalic cuticle. A comparison with the literature is made to elucidate corresponding structures within the cephalic capsules of representatives of Desmodorida. It is demonstrated that the presence of a cephalic cuticle is of no systematic value above the genus level. Accepted: 3 March 1996     

Ultrastructure and function of the pharynx of Gnathostomula paradoxa (Gnathostomulida)

 The pharynx of Gnathostomula paradoxa consists of the partly syncytial pharyngeal musculature, a pharyngeal epithelium, myoepitheliocytes, receptors, nerves, and three solid parts, called the jugum, the basal plate, and the jaw. Extended non-contractile regions of both pharyngeal and body wall musculature form the so-called parenchymatous tissue between the digestive tract and the body wall. The pharyngeal epithelium mediates the force from the pharyngeal musculature to the solid parts. The basal plate and jaw contain longitudinal cuticular rods which are elastic antagonists of the musculature. There is no buccal ganglion in G. paradoxa. The study supports the monophyly of the Gnathostomulida and Gnathifera. Accepted: 4 April 1997     

Dioctowittus spp. Chabaud and Le Van Hoa 1960 (Nematoda: Adenophorea) from Australian snakes

Dioctowittus denisoniae n. sp. from Denisonia punctata differs from D. wittei and D. chabaudi in the smaller size, lack of vestigeal male precloacal sucker, short egg-filaments, the presence of lateral expansions at the posterior end in the male, and in the expansions of the oesophageal tissue between the stichocytes. Dioctowittus sp. from Liasis amethystimus differs from the three described species in the posession of lateral lobes at both extremities.     

Ultrastructure of introvert and pharynx of Halicryptus spinulosus (priapulida)

The introvert of Halicryptus spinulosus bears three kinds of sensilla: buccal papillae, ordinary scalids, and dentoscalids. They are all characterized by bipolar monociliary receptor cells. The former two have apical openings at which the sensory cilia are in close contact with the ambient sea water. The pharyngeal teeth are composed of slender epithelial cells the tips of which are devoid of organelles and a thick cuticle. The anatomy of the muscle arrangement of the pharynx is described. Glands occur at the junction of the pharynx and midgut.     

Ultrastructure of the contact surfaces of Passalurus ambiguus (Rudolphi, 1819) (Nematoda)

The ultrastructure of the contact surfaces (integument and intestinal wall) of the nematode Passalurus ambiguus has been studied. The integument is composed according to the scheme common for all nematodes and includes a cuticle, hypodermis and a muscular layer. The specificity is with regard to the epicuticle, the different number of the cuticular sublayers in the anterior, central and the posterior parts of the worm body and the absence of a basal cuticular membrane. The intestinal wall consists of epithelial cells with microvilli. The ultrastructural characteristics of both contact surfaces indicate their main functions--absorption, secretion, transport, protection, movement, etc.     

Ultrastructure of the photoreceptor of Diplolaimella sp. (Nematoda)

The photoreceptor of the free-living marine nematode Diplolaimella sp. is ultrastructurally described. The most prominent feature of the photoreceptor is called the 'ocellar complex' and is composed of three dorso-laterally located parts. (1) The lens is an amorphous half sphere-shaped structure, about 1.5 mum in diameter. (2) The receptoral part is a stack of slightly undulating lamellae, localized just posterior to the lens. (3) The receptoral part is surrounded by a pigment cup containing electron-dense granules of 0.1-0.3 mum diameter. These three parts are embedded in a cell process, which has a more sizeable ventral extension containing the nucleus and cytoplasm characterized by a lot of free ribosomes and broad cisternae of the granular endoplasmic reticulum. This sheath cell is supposed to synthesize the pigment. The above described structure occurs bilaterally paired, some 50 mum from the anterior end.     

Ultrastructure of Coelomocytes in Sphaerolaimus gracilis de Man, 1876 (Nematoda)

The structure of coelomocytes in the adenophorean aquatic nematode Sphaerolaimus gracilis de Man 1876 was studied with light and electron microscopes. Acid phosphatase and catalase activities were demonstrated by electron microscopy. Two pairs of coelomocytes occurred laterally posterior to the esophagointestinaljunction. The anterior pair of the coelomocytes, with the renette cell and gonad, lay in either the left or the right lateral side of the body. The posterior pair of coelomocytes was in the opposite side of the body, usually posterior to the renette. A long, thin, cell-extension-like structure appeared to originate from the coelomocytes. Coelomocytes were characterized by specialized organelles (CC-organelle) and large vacuoles. The CC-organelle contained crystalline structures like those in peroxisomes. Acid phosphatase and catalase activities were detected in the matrix of CC-organelles and catalase activity in the vacuoles. It was assumed that vacuoles originate from the CC-organelles. Coelomocytes showed pinocytotic activities, and numerous vesicles were observed between the cell membranes and the vacuoles.     

Structure of the pharynx in the adult nematode Anguillicoloides crassus (Nematoda: Rhabditida)

The structure of the pharynx of the adult female nematode Anguillicoloides crassus (Spirurina) has been studied for the first time using light and transmission electron microscopy. The cylindrical pharynx consists of a short anterior muscular corpus and an enlarged posterior glandular and muscular postcorpus. The main cellular components of the pharynx of A. crassus include the muscle cells, the marginal cells, the nerve cells, and 1 dorsal and 2 subventral glands. New observations for nematodes include: (1) the non-contractile regions of pharyngeal musculature in the corpus have specific appearance; (2) the ventrosublateral longitudinal nerve in the pharynx has an enlarged, enucleated anterior part, with a pronounced palmate projections; and (3) abundant lysosomelike membranous bodies consisting of myelinlike figures of varied size present in marginal cells and pharyngointestinal valve. The 2 subventral glands and, apparently, the single dorsal gland, have their openings at the same level, i.e., at the border between the corpus and postcorpus. The pharyngeal-intestinal valve joins the pharynx to the intestine. Knowledge of the ultrastructure of these complex characters may be useful in understanding of functional features, and for comparative morphology as well as evolutionary considerations within the Chromadorea.     

Aspects on the Ultrastructure of the Cephalic Region in Two Species of Acrobelinae (Nematoda,Cephalobidae)

The lip structures termed labial probolae, characteristic for the subfamily Acrobelinae, and the anterior sense organs have been studied by electron microscopy. The labial probolae consist of an amorphous tissue with denser strengthenings. They do not contain any sensory structures or musculature. The anterior sense organs consists of: (1) six inner labial sensilla, each with one receptor ending in a pore on a papilla; (2) six outer labial sensilla, each with one receptor ending in the cuticle; (3) four cephalic sensilla, each with two receptors, one ending in a pore on a papilla and the other in the cuticle; (4) two amphids, each with 12 sensory neurons basally; (5) accessory sensilla ventro-laterally. The combination of several chemoreceptive anterior sensilla and the morphological diversity of the labial probolae within the subfamily may aid in the utilization of different soil microhabitats.     

Ultrastructure of the trophosome, a food-storage organ in Gastromermis boophthorae (Nematoda: Mermithidae)

The ultrastructure of the trophosome of Gastromermis boophthorae (Welch & Rubzov, 1965) is described at selected points in the life cycle of this mermithid nematode. The trophosome is grossly modified for the assimilation and storage of nutrients, and comparison is made with a generalised nematode intestine, with which it may be homologous. At its maximum development the trophosome is a solid syncytial cylinder which almost fills the body cavity of the nematode. Internally it is packed with nutrient reserves, whilst the outer cytoplasmic layer exhibits features indicative of transport functions. The trophosome is linked to the hypodermis of the body wall by radially-orientated cytoplasmic bridges, and the possible significance of this arrangement is discussed in relation to the nutritional function of the trophosome.     

Ultrastructure of the nerve-muscle junction in the pharynx of the earthworm,Lumbricus terrestris

Summary InLumbricus terrestris the wall of the pharynx is built up from obliquely striated longitudinal and circular muscle layers. The occurrence of perikarya and nerve bundles showing green fluorescence suggests the presence of aminergic innervation in the pharynx. A significant number of chemical synapses were detected in the neuropil among axon terminals. The junctional gap is generally 100–300 nm wide in type I junctions which resemble the cholinergic motor endplates of vertebrate skeletal muscle. A narrow junctional gap of about 25 nm is characteristic of the close contacts in the type II neuromuscular junction. Agranular spherical vesicles, together with small and large dense-cored granules, fill in these axon terminals.     

Ultrastructure of the anterior sense organs of adult Gastromermis boophthorae (Nematoda: Mermithidae)

The amphids of adult Gastromermis boophthorae exhibit an organization unlike any previously reported. Each amphid consists of a distal cuticular channel which opens to the exterior, and a proximal amphidial gland. The cuticular channel is double and 15–18 cilia are held in a tight bundle by the inner channel. The amphidial gland contains an extensive reticulum, and the nerve axons which give rise to the amphidial cilia are arranged around the outside of the gland; anteriorly these axons are characteristically flattened. A granular secretion is produced by the amphidial gland and passes via the reticulum to the double cuticular channel, thus bathing the ciliary bundle. The ultrastructure of the amphids is discussed in relation to functional considerations.     

Mastophorus muris (Nematoda: Spirurina): Ultrastructure of somatic muscle development

Hamada G. S. and Wertheim G. 1978. Mastophorus muris (Nematoda: Spirurina): ultrastructure of somatic muscle development. International Journal for Parasitology8; 405–414. The ultrastructure of the somatic muscle cells of the adult and six developmental stages of Mastophorus were studied. In all stages the cells consisted of a contractile region containing myofibrils separated by dense bands and a noncontractile region with nuclei, mitochondria, glycogen, lipid droplets and vesicles. Two sizes of myofilaments were present. The dense band contained T tubules and sarcoplasmic reticulum, and, in more advanced stages, support filaments, glycogen and dense bodies. The contractile region of the adult muscle cell consisted of several hundred irregularly shaped myofibrils arranged in a random pattern. This pattern of myofibrils was defined as irregular-coelomyarian. The third stage larva had a shallow-coelomyarian myofibril configuration, which changed to coelomyarian in the late third stage through the addition of new myofibrils at the apical contractile border. In the fourth stage larvae, the subdivision of existing myofibrils changed the pattern to irregular-coelomyarian.     

Ultrastructure of the rectum of infective-stage Wuchereria bancrofti (Nematoda: Filarioidea).

The authors have examined the ultrastructure of the rectum of infective-stage Wuchereria bancrofti by transmission electron microscopy. Our observations show that the rectum is divided into anterior and posterior segments. The cells of the anterior rectum appear to be derived from the microfilarial R (rectal) cells described by other authors. In both stages, these cells show voluminous nuclei, abundant mitochondria, and small cytoplasmic processes which contain fibrillar components. Amorphous material associated with these processes appears throughout the larval rectum and may protrude from the anus as the rectal plug. In the specimens examined, a patent lumen could not be traced completely through the anterior rectum. The posterior rectum has no counterpart in published accounts of microfilarial ultrastructure and probably arises during larval morphogenesis; it is lined with invaginated body cuticle, overlaid by a single layer of epithelial cells which may be of hypodermal origin.     

Three-dimensional reconstruction of the nose epidermal cells in the microbial feeding nematode, Acrobeles complexus (Nematoda: Rhabditida)

The epidermis of the anterior end (nose) plays an important role in the evolution, development, and functional feeding morphology in nematodes, but information on this complex organ system is limited. Here, we produce a 3D model of 13 of the cells making up this organ system reconstructed from serial transmission electron micrographs of the microbial feeding nematode, Acrobeles complexus. Nose epidermal cells were found to be broadly similar to those of the distantly related model organism Caenorhabditis elegans in the number and arrangement of nuclei in these largely syncytial cells; this similarity demonstrates striking evolutionary conservation that allows for robust statements of homology between the taxa. Examining details of cell shape, however, revealed surprisingly complex subcellular specialization, which differed markedly from C. elegans in the number and arrangement of cell processes. Anterior toroid processes of the anterior arcade, posterior arcade, and HypB syncytia form a nested complex at the base of the labial probolae. Anterior toroid processes of HypC and the inner labial socket cells are associated with the base of the cephalic probolae and radial ridge processes. Extracellular filaments (tendon organs) and radiating cytoskeletal filaments of the posterior arcade syncytium form a connection between the body wall muscle cells and the pharynx. An epidermal cell with no known homolog in other nematodes is identified. Findings provide a basis to propose hypotheses related to the development and evolutionary origin of specialized feeding appendages (probolae) in the Cephalobinae (including Acrobeles), and hypotheses of homology are revised for epidermal cells in the nose of the closely related and primarily plant parasitic group, Tylenchida.