Comparative ultrastructural study of the cuticle and spermatozoa in Propappus volki Michaelsen, 1916 (Annelida: Clitellata)

The ultrastructure of the cuticle and mature spermatozoa of the oligochaete Propappus volki Michaelsen, 1916 is described with the aim of providing additional data for clarifying the systematic position of the taxon. P. volki is a fresh-water species living in streams, and is easily recognized by its proboscis on the pre-segmental prostomium and, in mature specimens, by a clitellum covering the segments XII–XIV. The cuticle is composed of a proximal fibre zone and a distal layered epicuticle covered with membrane-bound epicuticular projections. The fibre zone consists of collagenous fibres in a matrix, arranged in either densely packed parallel layers with the fibres oriented in the same direction, or with more loosely distributed fibres, although with the same main orientation. The epicuticular projections are pyramidal with the base leaning on the outer surface of the epicuticle. The cuticle covering the proboscis differs in morphology from that of the rest of the worm; the fibre zone is composed of thin and short fibrils running in all directions, and the epicuticular projections are longer and more narrow than the projections in other regions of the worm.

The spermatozoa are filiform cells formed, in sequence, by an acrosome, an elongated nucleus, a long midpiece, and a flagellum. The acrosomal tube is short and straight with a completely external acrosomal vesicle. Following the acrosome is a apically corkscrew-shaped and basally straight nucleus. The midpiece is twisted and formed by five mitochondria. The flagellum shows a prominent central sheath arrangement.

A comparison with ultrastructurally described cuticles and spermatozoa from other clitellate species reveals most similarities with enchytraeids.     

An ultrastructural study of the cuticle in the marine annelid Heterodrilus (Tubificidae, Clitellata)

The ultrastructure of the cuticle in four species of the marine Heterodrilus (H. paucifascis, H. pentcheffi, H. flexuosus, H. minisetosus) is investigated with transmission electron microscopy. The noncellular cuticle consists of several parts; closest to the epidermis is a thick zone of collagen fibers embedded in a matrix. The matrix continues outside the fiber zone, forming a layered epicuticle. The external surface of the epicuticle is covered by evenly distributed, membrane-bound bodies, termed epicuticular projections. The epicuticular projections have their longitudinal axis perpendicular to the surface of the cuticle and are attached to the surface by either the surrounding membrane itself or by short pedestals. Microvilli, extensions from the epidermal cells, penetrate and sometimes pass completely through the cuticle. There is interspecific variation in the morphology of the cuticle. The four studied species differ in the arrangement of the collagen fibers, from irregularly distributed fibril bundles to orthogonally arranged fiber layers, as well as in the number and density of layers in the epicuticle. One of the studied species, H. paucifascis, shows intraspecific variation, which is associated with sample locality. The Bahamian specimens of H. paucifascis have four layers in the epicuticle, club-shaped epicuticular projections, and collagen fibers forming a less defined orthogonal grid, while the Belizean specimens have three layers in the epicuticle, epicuticular projections with a bulging part at midlevel, and a distinct orthogonal grid. Based on these findings the variation in the morphology of the cuticle appears to be dependent on both phylogenetic constraints, and functional and environmental factors.     

Cuticular ultrastructure in some marine oligochaetes (Tubificidae)

Abstract. The ultrastructure of the thin, non-cellular cuticle is described for 6 marine oligochaetes, representing 3 of the subfamilies (Phallodrilinae, Limnodriloidinae, and Rhyacodrilinae) of the Tubificidae. The main components of the cuticle in these 6 species, as in most other oligochaetes examined, are: (1) a fiber zone closest to the epidermis, consisting of collagen fibers embedded in a matrix, (2) an epicuticle, which is a continuation of the matrix outside the fiber zone, and (3) epicuticular projections, which are membrane-bound bodies covering the outer surface of the epicuticle. The projections are probably formed by the microvilli that penetrate the cuticle from the epidermal cells below, but this was confirmed only in the studied limnodriloidines. Three of the species examined, Duridrilus turdus, Olavius vacuus , and Heterodrilus paucifascis , lack microvilli. The morphology of the components in the cuticle differs between the studied species. The collagen fibers may form an "orthogonal grid" (i.e., layers of parallel fibers perpendicular to the layers immediately above and below), or they may form parallel layers, or be irregularly scattered. The number of dense layers in the epicuticle, as well as the shape and internal structure of the epicuticular projections, also vary. All these characters might be useful in future phylogenetic analyses to achieve better hypotheses of relationships within oligochaetes as well as to other groups.     

Comparative study of the cuticle in some aquatic oligochaetes (Annelida: Clitellata)

An examination of the cuticle of six aquatic oligochaete species using transmission electron microscopy revealed a larger morphological variation than previously known. Three freshwater species, Aulodrilus pluriseta, Spirosperma ferox (both Tubificidae), and Pristina breviseta (Naididae), and three marine species, Clitellio arenarius, Heterochaeta costata (both Tubificidae), and Paranais litoralis (Naididae), were investigated. The arrangement of the collagen fibers in the cuticle differs among the studied species. Only S. ferox shows an "orthogonal grid," i.e., layers of parallel fibers perpendicular to each other, as earlier described for lumbricids and enchytraeids. Clitellio arenarius and H. costata have fibers arranged in layers, while A. pluriseta and P. litoralis have irregularly distributed fibers. Pristina breviseta lacks cuticular fibers. The matrix surrounding the collagen fibers (when present) continues outside the fiber layer, making up a thin epicuticle, which has a unique banding in each of the studied species. The external surface of the epicuticle is covered with epicuticular projections. Their number, shape, and attachment to the epicuticle vary among the studied species. Furthermore, a distinctive internal substructure of the projections was observed in H. costata, A. pluriseta, S. ferox, and P. breviseta. Microvilli, extensions from the epidermal cells, penetrate the cuticle and terminate at its outer surface. In three species microvilli were observed to pinch off the epicuticular projections. The size, number, and shape of the latter vary; no typical microvilli were observed in S. ferox.     

Ultrastructural shape and three-dimensional organization of the intracuticular canal systems in the mineralized cuticle of the green crab Carcinus maenas

Two main self-contained canal systems are present in the crab mineralized cuticle. The first, or fibre canal system, is constituted by simple, unbranched vertical canals containing axially running fibres in close association with myoepidermal junctions. The second, or pore canal system, is composed of procuticular pore canals and epicuticular channels that prolong the procuticular canals. In opposition to widespread opinion, pore canals make up a three-dimensional branched system extending from the apical plasma membrane of the epidermis up to the epicuticle. Branching occurs by projections of lateral horizontal from the vertical canals at the lower level of the pigmented layer and by innumerable ramifications of epicuticular canals. In agreement with Neville's model for insects, vertical procuticular pore canals of crustacean mineralized cuticle, and also fibre canals, exhibit a twisted ribbon structure reflecting the helicoidal arrangement of the horizontal chitin-protein microfibrils.     

Elektronenmikroskopische Untersuchungen anAnaitides mucosa (Annelida,Polychaeta). Cuticula und Cilien,Schleimzellen und Schleimextrusion

Two components, a basal cuticle and an epicuticle, make up the cuticle ofA. mucosa. The basal cuticle consists of collagen fibrils, which are arranged in about 20 layers. The orientation of the fibrils changes rectangularly from one layer to the next. Fine filaments interweave the basal cuticle. The epicuticle, which is covered by a layer of electron dense material, is composed of irregularly arranged thin filaments. Branched microvilli of the epidermal cells penetrate the cuticle. Bacteria are found in the basal cuticle. Dorsally each segment has a band of densely packed smooth cilia. Laterally and partly ventrally aggregates of cilia are observed. These cilia exhibit apically artificial swellings. At least six different mucous cells are observed in the epidermis, morphologically distinguishable by the structure of the secretion products. Mucus is secreted via exocytosis through cuticular pores. During this process the mucus might expand. The secreted mucus consists of filamentous subunits.     

Ultrastructural organization of hypodermis and formation of cuticle in pharate larva of Leptotrombidium orientale (Acariformes: Trombiculidae)

The ultrastructural organization of hypodermis and the process of cuticle deposition is described for the pharate larvae of a trombiculid mite, Leptotrombidium orientale, being under the egg-shell and prelarval covering. The thin single-layered hypodermis consists of flattened epithelial cells containing oval or stretched nuclei and smooth basal plasma membrane. The apical membrane forms short scarce microvilli participating in the cuticle deposition. First of all, upper layers of the epicuticle, such as cuticulin lamella, wax and cement layers, are formed above the microvilli with plasma membrane plaques. Cuticulin layer is seen smooth at the early steps of this process. Very soon, however, epicuticle starts to be curved and forms particular high and tightly packed ridges, whereas the surface of hypodermal cells remains flat. Then a thick layer of the protein epicuticle is deposited due to secretory activity of hypodermal cells. Nearly simultaneously the thick lamellar procuticle starts to form through the deposition of their microfibrils at the tips of microvilli of the apical plasma membrane. Procuticle, as such, remains flat, is situated beneath the epicuticular ridges and contains curved pore canals. Cup-like pores in the epicuticle provide augmentation of the protein epicuticle mass due to secretion of particular substances by cells and to their transportation through the pore canals towards these epicuticular pores. The very beginning of the larval cuticle formation apparently indicates the starting point of the larval stage in ontogenesis, even though it remains for some time enveloped by the prelarval covering or sometimes by the egg-shell. When all the processes of formation are over, hungry larvae with a fully formed cuticle are actively hatched from two splitted halves of prelarval covering.     

Etude ultrastructurale de l'évolution du tégument de la Sangsue Hirudo medicinalis L. (Annélide,Hirudinée) au cours d'un cycle de mue / Developmental changes in the integument of the leech Hirudo medicinalis L. (Annelida,Hirudinea) during a molting cycle. An ultrastructural study

Summary

The integument of the leech Hirudo medicinalis is mainly composed of a single layer of cuticle-secreting epidermal cells. The cuticle is made up of collagen fibers which support a layer of membrane-bound epicuticular projections.

Shedding of the old cuticle is preceded by the formation of a new cuticle. The epicuticular projections are the first to develop: they originate from the tips of numerous microvilli of the epidermal cells. As soon as it appears, the newly-formed collagen layer is firmly attached to the epidermal cells by numerous hemidesmo-somes, whereas the old cuticle is no longer connected with the epidermal surface. The epidermal cells exhibit marked characteristics of secretory activity during the laying down of the new cuticle.

The observations are discussed in connexion with recent findings of high ecdysteroid levels in leeches at the beginning of the molting cycle.     

棉铃虫性外激素分泌腺的研究

棉铃虫Helicoverpa armigera Hubner雌蛾的性外激素分泌腺是一个完整的上皮环,位于第八、九腹节之间。羽化2天雌蛾的腺体细胞方形,比未分化的上皮细胞大。腺体折皱,表面密布小毛,小毛无孔。表皮可分二层：上表皮和内表皮。上表皮致密,较薄,厚度均匀。内表皮厚度有变化,较厚,由12-14层呈螺旋状排列的几丁微丝组成,有上皮丝穿人,构成孔道。顶部细胞膜组成微绒毛,底部细胞膜有内折。细胞质内有粗面内质网,光面内质网,高尔基氏复合体、脂肪滴、糖原及线粒体等细胞器。大的细胞核位于中下部。     

胡氏边白蚁消化系统的微细构造

胡氏边白蚁Marginitermes hubbardi(Banks)消化系统可分为前肠、中肠及后肠三大段.前肠包括葡萄状唾腺、口、咽喉、食道、前胃及贲门瓣;从贲门瓣开始到马氏管着生处为止这一段为中肠;后肠则分为葫芦形胃、结肠、直肠和肛门.其消化系统的特点:在前、后肠有几丁内膜、细胞层上还有一层微绒毛;上皮细胞底膜内陷很深,折叠中夹着许多线粒体;中肠围食膜表面有几丁层一直延伸到后肠;后肠前端膨大的葫芦胃中共生了很多种细菌及原生动物,共生的细菌、动物分泌纤维素酶帮助它消化木质纤维.     

The fine structure and deposition of the larval cuticle of the sheep blowfly (Lucilia Cuprina)

The cuticle of Lucilia is composed of an untanned endocuticle and a complex epicuticle of four layers, superficial layer, outer epicuticle, cuticulin and dense layer. The outer epicuticle and attached epicuticular filaments are resistant to acid hydrolysis. During deposition of the cuticle of each larval instar, the cuticulin and dense layers are formed first, followed by the outer epicuticle, which appears to be laid down by secretions from the epidermis passing through the cuticulin via epicuticular filaments. The outer epicuticle is found in the position normally occupied by the wax layer of other insect species.     

Fine structure and morphogenesis of the sclerite epicuticle in the Atlantic shore crab Carcinus maenas

Three basic sublayers are identified in the epicuticle of the mineralised sclerites of the Atlantic shore crab Carcinus maenas (Crustacea, Decapoda): the surface coat, the cuticulin layer, and the inner epicuticle. Their morphogenesis and subsequent changes are described throughout the moulting cycle in the normal cuticle and the cuticular structures, namely the sensory bristles and epicuticular spines. At first, the cuticulin layer begins to form just after apolysis. This layer is built directly over the plasma membrane and immediately appears as a membrane-like structure 40 nm thick, composed of five symmetrically arranged laminae: two inner electron-lucent leaflets sandwiched between two thick electron-dense leaflets and separated by a thin dense median stratum. Elaboration of the inner epicuticle below the cuticulin layer is thought to occur via an intussusceptive process involving the pore canal cell extensions as transport routes. The inner epicuticle is made of vertically oriented microfibres embedded in an electron-dense matrix material. During the second half of the premoult period, the surface coat is deposited on the upper side of the cuticulin layer.     

Formation of the hindgut cuticular lining during embryonic development of Porcellio scaber (Crustacea,Isopoda)

The hindgut and foregut in terrestrial isopod crustaceans are ectodermal parts of the digestive system and are lined by cuticle, an apical extracellular matrix secreted by epithelial cells. Morphogenesis of the digestive system was reported in previous studies, but differentiation of the gut cuticle was not followed in detail. This study is focused on ultrastructural analyses of hindgut apical matrices and cuticle in selected intramarsupial developmental stages of the terrestrial isopod Porcellio scaber in comparison to adult animals to obtain data on the hindgut cuticular lining differentiation. Our results show that in late embryos of stages 16 and 18 the apical matrix in the hindgut consists of loose material overlaid by a thin intensely ruffled electron dense lamina facing the lumen. The ultrastructural resemblance to the embryonic epidermal matrices described in several arthropods suggests a common principle in chitinous matrix differentiation. The hindgut matrix in the prehatching embryo of stage 19 shows characteristics of the hindgut cuticle, specifically alignment to the apical epithelial surface and a prominent electron dense layer of epicuticle. In the preceding embryonic stage – stage 18 – an electron dense lamina, closely apposed to the apical cell membrane, is evident and is considered as the first epicuticle formation. In marsupial mancae the advanced features of the hindgut cuticle and epithelium are evident: a more prominent epicuticular layer, formation of cuticular spines and an extensive apical labyrinth. In comparison to the hindgut cuticle of adults, the hindgut cuticle of marsupial manca and in particular the electron dense epicuticular layer are much thinner and the difference between cuticle architecture in the anterior chamber and in the papillate region is not yet distinguishable. Differences from the hindgut cuticle in adults imply not fully developed structure and function of the hindgut cuticle in marsupial manca, possibly related also to different environments, as mancae develop in marsupial fluid. Bacteria, evenly distributed within the homogenous electron dense material in the hindgut lumen, were observed only in one specimen of early marsupial manca. The morphological features of gut cuticle renewal are evident in the late marsupial mancae, and are similar to those observed in the exoskeleton.     

La cuticule proctodéale des Insectes

Résumé L'ultrastructure de la cuticule du rectum a été étudiée chez onze espèces d'Insectes, appartenant à neuf ordres. On s'est surtout intéressé aux espèces présentant des papilles rectales; dans ce cas on distingue toujours trois types de cuticule: cuticule de l'épithélium rectal, cuticule des papilles, cuticule du cadre entourant les papilles.La cuticule du cadre est formée d'une masse compacte et amorphe, sclérifiée, surmontée d'une cuticuline de structure normale.Les deux autres types de cuticules possèdent une structure plus classique: épicuticule comprenant cuticuline et zone dense, et endocuticule. La cuticule de l'épithélium rectal a toujours une structure comparable à celle d'une cuticule périphérique non sclérifiée. La cuticule des papilles est plus variable, et toujours différente de celle de l'épithélium rectal. Ces différences portent sur la cuticuline, la zone dense, les filaments épicuticulaires; l'endocuticule sur les papilles montre une organisation fibrillaire moins nette, qui paraît corrélative d'une réaction positive à l'APS. Des canaux poraires n'ont jamais été observés dans la cuticule des papilles; il en existe quelquefois dans la cuticule de l'épithélium rectal. Une sous-cuticule, contenant des mucopolysaccharides acides, est présente dans certains cas dans les deux types de cuticule.Dans les espèces ne possédant pas de papilles rectales, il n'existe qu'un seul type de cuticule rectale, variable suivant l'espèce.La cuticule des papilles montre, dans certaines espèces, des dépressions superficielles, d'un diamètre voisin de 0,2 , réparties uniformément mais sans ordre défini (dépressions épicuticulaires). De telles dépressions s'observent aussi dans quelques espèces dépourvues de papilles (Tenebrio). Au niveau de ces dépressions, la cuticuline a une structure particulière et la zone dense est réduite.Les rapports entre structure et perméabilité de la cuticule sont discutés. On envisage en particulier les rôles respectifs de la cuticuline, de la zone dense, des filaments épicuticulaires et des dépressions épicuticulaires.

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Proctodeal cuticle of InsectsI. Comparative ultrastructure

Summary The ultrastructure of the rectal cuticle was studied in eleven species of Insects from nine orders. Special attention was given to those having rectal papillae. In such species, three types of cuticule were observed: 1) the cuticle of the rectal epithelium, 2) the cuticle of the papillae, 3) the cuticle of the border of the papillae.The cuticle of the border is made of a compact amorphous substance, which is sclerotized and covered by a typical cuticulin layer.The two other types of cuticle exhibit a more conventional organization, namely the epicuticle comprising both the cuticulin and the dense layer, and the endocuticle. The cuticle of the rectal epithelium is similar to unsclerotized external cuticle. The cuticle of the papillae is more variable and always differs from the cuticle of the rectal epithelium. Variations occur with regards to the cuticulin, the dense layer and the epicuticular filaments. The endocuticle of the papillae has a less conspicuous fibrillar structure which we believe is correlated with the PAS-positive reaction found in this endocuticle. Pore canal sometimes are observed in the cuticle of the rectal epithelium but never above the papillae. In some cases, a sub-cuticular layer containing acid mucopolysaccharids is present in the two types of cuticle.In species lacking rectal papillae, the rectal wall is covered by only one type of cuticle, the features of which vary according to species.In some Insects, the cuticle of papillae shows numerous superficial depressions, each of about 0.2 in diameter. These epicuticular depressions are uniformly distributed throughout the papillae but are not arranged in any particular pattern. We have also found such depressions in other Insects lacking rectal papillae (e.g. Tenebrio). In the epicuticular depressions, the cuticulin exhibits a modified organization and the dense layer is reduced.The relations between ultrastructure and cuticular permeability are discussed. The possible roles of the cuticulin, the dense layer, the epicuticular filaments and the epicuticular depressions are examined.

     

Ultrastructure of the midgut and the adhering tubular salivary glands of Frankliniella occidentalis (Pergande) (Thysanoptera : Thripidae)

The ultrastructure of the midgut and the tubular salivary glands of Frankliniella occidentalis (Thysanoptera : Thripidae) is described. The microvilli have 2 different types of glycocalyx: in the anterior part of the midgut they are surrounded by a myelin-like membrane; in the posterior region, the microvilli have numerous rod-like projections arranged to form a continuous layer. Microfilaments longitudinally cross each microvillus; the microfilaments contain F-actin. Tubular salivary glands flank the midgut but do not fuse with it. The distal part of these glands have microvillated cells containing large amounts of electron-transparent material. The cells of the proximal part are lined with a thin cuticle.     

High-resolution scanning electron microscopic study of the mouse submandibular salivary gland.

The submandibular gland of the mouse was studied by high-resolution scanning electron microscopy, using the osmium-dimethylsulfoxide-osmium method. The three-dimensional structures of the intracellular membranous organelles of acinar cells were clearly revealed. The luminal surface of cisterns of the granular endoplasmic reticulum and Golgi apparatus exhibited particles of 8-15 nm in diameter. The secretory canaliculi presented short microvilli which were irregularly arranged. The striated duct cells were characterized by rich mitochondria arranged vertically in the basal portion. The lamellar mitochondrial cristae were noted in three-dimensional images. The luminal surface extended short microvilli, while that of the excretory duct cell presented complicated microplicae. The capillary endotheliocytes showed a few short microvilli, and their fenestrated areas were bordered by cytoplasmic crests. Fenestrae were 50-80 nm in diameter and showed a plug in their center. The basement membranes of the acini and capillaries showed a spongy structure with various strands and meshes. Collagenous fibrils crisscrossed on their surface.     

Some implications of helical fibres in worm cuticles

The cuticles of many worms contain a cylindrical trellis made of layers of collagen fibres wound round the body in left- and right-hand helices. This kind of extensible skeletal structure imposes various constraints on a worm's behaviour, and some of these are examined, using the nematomorph Parachordodes woltersforffii as the main example. Upon extension or shortening of the cuticle, neighbouring fibres in one layer will eventually touch and so limit further movement; this in turn affects the extent of shortening, elongation, bending and coiling of the whole worm. Simple equations relate: the angle between a fibre and the worm's long axis; fibre spacing and radius; worm body radius and radius of curvature. The relevance to the life of the worm of fibre arrangement, matrix properties and volume changes is discussed.     

A fine structural analysis of the epidermis and cuticle of the oligochaete aeolosoma Bengalense stephenson

The fine structure of the epidermis and cuticle has been described for the oligochaete Aeolosoma bengalense. The epidermis is a pseudostratified epithelium and consists of the following cell types: ciliated and nonciliated supportive cells, pigment cells and associated satellite cells, mucous cells, basal cells, and ciliated non-supportive columnar cells. Overlying and restricted to the supportive cells is a delicate cuticle composed of: (a) a discontinuous layer of membrane-bounded surface particles; (b) a thin filamentous layer of moderate electron density just under the surface particles; (c) a thicker inner filamentous layer of low electron density. Digestion with pronase effectively removes the cuticle. This, together with the fact that it stains with alcian blue and ruthenium red, indicates that the cuticle contains an acid mucopolysaccharide. Regeneration of the cuticle, following pronase treatment, is marked by the elaboration of numerous microvilli by the supportive cells. Most of the microvilli are transitory and evidence supports a microvillar origin for the cuticular surface particles. The presence of cuticular surface particles may be a characteristic shared in common by all oligochaetes and, perhaps, some polychaetes.     

Supercoil of collagen fibrils in the integument of Alvinella, an abyssal annelid

The polychaete annelid Alvinella pompejana was discovered near the hydrothermal vents, recently explored in the Eastern Pacific Ocean. This worm is protected by a cuticle deeply transformed over certain areas of the body and some changes are due to the presence of a very special bacterial flora. The present work however deals mainly with the supercoiled collagen fibrils, which are well visualized in thin sections observed by transmission electron microscopy. This character strongly differentiates this species from other annelids and worms in general, the cuticle of which includes straight and apparently non-coiled collagen fibrils. This indicates that fibrils are extensible in Alvinella, possibly under physiological conditions, and that internal pressure and local volume variations are regulated according to principles which depart from what is recognized in other worms, where cuticular fibrils are considered as inextensible. Possible models of this cuticle are discussed and particularly aspects which show a relationship with certain liquid crystals. Very different factors may be involved in morphogenesis of such cuticles: microvilli distribution, self-assembly of collagen fibrils, mechanical constraints. An appendix recalls some classical data on worm cuticle geometry and presents an estimate of volume variations resulting from coiling of fibrils.