An ultrastructural and cytochemical study of the digestive system in Oxyposthia praedator (Turbellaria,Acoela)

The central parenchyma in Oxyposthia praedator consists of multifunctional cells. These cells digest food material intracellularly, can effect extracellular digestion through release of digestive enzymes by cell lysis and clasmatosis, and synthesize reserve nutritional substances.     

The proventriculus of the carpenter bee, Xylocopa virginica virginica (L.), with special reference to bacteria-containing luminal tunnels

Abstract. Four tunnels off the lumen of the proventriculus of the carpenter bee, Xylocopa virginica virginica , have been discovered. Light and electron micrographs revealed the presence in the tunnels of gram-positive, rod-shaped bacteria, some of which showed division stages. The occurrence of the bacteria exclusively in the tunnels—not in the lumen of the proventriculus—makes speculation as to their function difficult. The function of the tunnels is also obscure, as no glands were seen emptying into them. The bacteria may be symbionts that release enzymes into the tunnels, which are subsequently transported to the midgut to aid digestion. They could also be parasites. This is the first report of such bacterial-containing tunnels in insects.     

Bacillus cereus B-02对Botrytis cinerea拮抗机理的研究

采用电子显微镜(扫描、透射)和激光扫描共聚焦显微镜,从细胞形态学和生理学水平上研究蜡样芽孢杆菌Bacillus cereus B-02过滤液对灰葡萄孢菌Botrytis cinerea的拮抗机理。结果表明,处理菌丝表面形态受到严重破坏,发生强烈变形;菌丝细胞核、线粒体和细胞壁等亚细胞结构发生了明显改变,细胞内出现大量无膜透明内含物,并产生较大液泡。此外,处理菌丝DNA、线粒体膜电位和活性氧荧光强度均低于对照组,且差异极显著;说明B-02菌株对病原真菌菌丝细胞DNA的合成、线粒体膜电位和活性氧水平有重要影响。     

Bacillus cereus B-02对Botrytis cinerea 拮抗机理的研究

采用电子显微镜(扫描、透射)和激光扫描共聚焦显微镜,从细胞形态学和生理学水平上研究蜡样芽孢杆菌Bacillus cereus B-02过滤液对灰葡萄孢菌Botrytis cinerea的拈抗机理.结果表明,处理菌丝表面形态受到严重破坏,发牛强烈变形;荫丝细胞核、线粒体和细胞壁等哑细胞结构发生了明显改变,细胞内出现大量无膜透明内含物,并产生较人液泡.此外,处理菌丝DNA、线粒体膜电位和活性氧荧光强度均低于对照组,且差异极显著;说明B-02菌株对病原真菌菌丝细胞DNA的合成、线粒体膜电位和活性氧水平有重要影响.     

Ultrastructure of muscle cells from a few selected turbellarians: possible correlations between form and function

A comparative ultrastructural study of muscle cells from several turbellarian species revealed a basic smooth type of construction, with thick and thin myofilaments. However, the distribution of contractile elements, "dense bodies", smooth reticulum, mitochondria, as well as junctional specializations was found to vary within different systems. This variability is probably related to greater or lesser physical demands on the musculature. From a mechanical viewpoint, the most ‘powerful’ muscular system studied was represented by the pharyngeal bulb of Geocentrophora applanata, in which muscle fibers were organized into a compact, square reticulum, hemidesmosomes occurred in large numbers, and myofilaments were grouped in patches reminiscent of A and I bands of striated muscles. At the other extreme, muscular fibrils of the catenulids studied were thin and regularly spaced along the body wall, and the branched ends of radial myofibrils in the parenchyma were connected to the epithelial layer. This revised version was published online in July 2006 with corrections to the Cover Date.     

Histology and ultrastructure of the gut epithelium of the neotenic cave salamander, Proteus anguinus (Amphibia, Caudata)

Histological, histochemical, and ultrastructural features of the gut of the European endemic cave salamander Proteus anguinus were studied. The gut is a relatively undifferentiated muscular tube lined with a simple columnar epithelium containing numerous goblet cells. The mucosa and underlying lamina propria/submucosa are elevated into a number of high longitudinal folds projecting into the lumen. The enterocytes are covered apically with uniform microvilli. Irregularity in the arrangement of microvilli was observed. Occasionally, irregular protrusions of the cytoplasm appear between groups of microvilli. Pinocytotic activity occurs at the bases of the intermicrovillous space. Mitochondria are numerous in the apical cytoplasm and basally beneath the nuclei. The supranuclear cytoplasm contains most of the cell organelles. The lateral plasma membranes of adjacent cells interdigitate and are joined by junctional complexes. The periodic acid-Schiff (PAS) reaction, indicating neutral mucosubstances, is positive only in the apical brush border of enterocytes and in goblet cells. The goblet cells also stained with Alcian blue (AB), at pH 2.5, thus revealing the presence of carboxylated glycosaminoglycans. Compact aggregations of AB- and PAS-negative cells are situated directly below the epithelium. Mitotic figures are present in individual clusters of cells. The fine structure of cells in these clusters indicated that these cells could be responsible for renewal of intestinal epithelium. Numerous endocrine-like cells could also be seen. The closely packed smooth muscle cells and amorphous extracellular material with collagen fibrils constitute a net-like structure under the basal lamina that is very closely associated with the epithelium. There are numerous acidophilic granular cells between epithelial cells, in the lamina propria/submucosa, and between cells aggregations. They seem to be associated with nematode infections and possibly constitute a humoral defense mechanism.     

The digestive tract of the amberjack Seriola dumerili, Risso: a light and scanning electron microscope study

The histology of the digestive tract of the amberjack ( Seriola dumerili , Risso) was studied using light and scanning electron microscopy. The anterior oesophagus mucosa displays primary and secondary folds lined with a stratified squamous epithelium with fingerprint-like microridges which is substituted, on the top of the oesogaster folds, by a simple columnar epithelium with short microvilli. Only primary folds are present in the stomach. The anterior portion is rich in simple tubular glands, whereas the oesogaster and the pyloric region are devoid of them. Pyloric caeca and anterior and middle intestine mucosa display the same pattern of folding. The dominant cell type is the enterocyte, which exhibits larger and thinner microvilli in the caeca than in the intestine. The columnar epithelium of the rectum is replaced, in the anal sphincter, by a stratified flattened epithelium. Goblet cells are numerous throughout the whole length of the tract with the exception of the initial part of the oesophagus, the oesogaster, the stomach and the anal sphincter. Mucosubstances have been shown to vary in the different regions of the gut: acid mucines are found in the oesophagus, pyloric stomach, caeca, intestine and rectum, whereas neutral mucosubstances dominate in the anterior portion of the stomach. The muscularis is well developed throughout the length of the tract: two layers of striated muscle at the oesophageal level; two layers of smooth muscle in the stomach wall and three at the intestinal level.     

Ultrastructural features of oogenesis in some marine neoophoran turbellarians

An ultrastructural study of oogenesis has been undertaken in some marine species of neoophoran turbellarians belonging to the Tricladida, Proseriata, and Prolecithophora. Among marine triclads, Cercyra hastata has oocytes with a remarkable amount of what appears to be autosynthetic proteinaceous yolk, while Procerodes dohrni and P. lobata have alecithal oocytes. Among the Proseriata, several species of the primitive family Monocelididae (subfamily Monocelidinae) have oocytes with a discrete amount of what appears to be autosynthetic yolk, while Parotoplana macrostyla, of the derived family Otoplanidae, has alecithal eggs. Finally preliminary observations on Plagiostomum maculatum (order Prolecithophora) suggest that oocytes have autosynthetic yolk globules.These results support the hypothesis (previously formulated on the basis of similar ultrastructural investigations on freshwater triclads) that the presence of autosynthetic yolk in some neoophoran turbellarians can be interpreted as a primitive character inherited from an ancestor with archoophoran organization. This plesiomorphic character would still be maintained in some species while lost in others following differentiation of vitellaria which are characteristic of the Neoophora.     

Anatomy and ultrastructure of the proboscis in Mesorhynchus terminostylis (Platyhelminthes,Rhabdocoela)

The ultrastructural organization of the proboscis in Mesorhynchus terminostylis is distinctly different from that in other members of the Polycystididae in which it is currently classified. The sheath epithelium is formed by three belts, all with intra-epithelial nuclei. The apical belt of the bipartite cone epithelium has a single intrabulbar nucleus, and the basal belt possesses five insunk nucleiferous cell parts behind the bulb. Six types of glands surface through the epithelia; the three types emerging through the cone epithelium can be homologized with those described for Polycistis naegelii. Only uniciliary receptors are found in the epithelium. The musculature in the bulb has a very loose appearance, and the bulbar septum appears to be a bipartite basement membrane. The septum can be considered the basement membrane of the cone epithelium as if the contractile portion of the inner longitudinal muscles have invaded the epithelium and come to lie between the epithelial cells and the basement membrane. Thus the inner musculature of the bulb is entirely intraepithelial as is the case for Psammorhynchus tubulipenis and Cytocystis clitellatus. The systematic position of M. terminostylisremains uncertain but seems to lie between Psammorhynchus and Cytocystis on one hand and Koinocystididae and Polycystididae on the other.     

Ultrastructural observations on paracnids. I: Coelogynopora axi Sopott (Turbellaria,Proseriata)

The Schlauchdrüsen or paracnids of Coelogynopora axi Sopott, 1972 consist of two components: a muscle cell and a secretory cell.The secretory cell is provided with a tube, which bears a border of microvilli. In the normal position the tube is situated in the interior of the secretory cell, and the microvilli stand at the inner side of the tube. After expulsion of the tube the microvilli are situated at its free surface.The evagination takes place in response to chemical stimuli and is effected by the contraction of the myofibrils of the muscle cell.The paracnids are supposed to be mechanisms of defense.However, conformities with nematocysts and spirocysts of the cnidarians do not exist.The paracnids in other species of the Coelogynoporidae, for example in Invenusta paracnida (Karling, 1966) and Carenscoilia bidentata Sopott, 1972 differ from those of C. axi in many details.Abbreviations bl- basement lamina - ep- epidermis - hd- hemidesmosomes - mc- muscle cell - mt- microtubules - mv- microvilli - nsc- nucleus of the secretory cell - sb- bowl containing secretion granules - sc- secretory cell - sd- septate desmosome-like structures - sg- secretion granules - t- tube - tf- tonofilaments     

Ultrastructure and functional morphology of a nematalycid mite (Acari: Actinotrichida: Endostigmata: Nematalycidae): adaptations to mesopsammal life*

Nematalycid mites have undergone extreme changes of body shape in adaptating to life in tiny spaces between grains of fine sand. Because of their minute size, the morphology of these organisms can only be reconstructed from ultrathin serial sections. The cuticle forms regular alternating palettes on the surface; such a structure may also function as a plastron. Movement of the body is effected by a continuous secondary muscle layer beneath the epidermis which operates in connection with the cuticular palettes. This movement represents a hitherto unknown mode of reptation, which can be understood as an adaptation to moving among sand particles. The appendages have been reduced to a minute size. The morphology of the digestive tract is described and conclusions are drawn concerning nutrition.     

Factors influencing otolith increment formation in Japanese eel,Anguilla japonica T. & S., elvers

The histology of the stomach of Tilapia nilotica (Linnaeus) collected from the R. Nile (Ismailia fork in Egypt) was examined using light microscopy and scanning electron microscopy. The study revealed that the gastric wall is composed of several tunicae: mucosa, submucosa, muscularis and serosa. The tunica mucosa is thrown up into a number of high longitudinal folds projecting into a lumen which is stellate in cross-section when empty. The mucosal surface has a mosaic appearance due to the hexagonal borders of the surface epithelial cells. The latter cells are characterized by the presence of a juxtanuclear vacuole and a PAS-positive brush border made of microvilli. Gastric pits (foveolae) are present as invaginations of the mucosal surface. The foveolar epithelium secretes neutral and acid mucins. Simple, straight, tubular unbranched gastric glands occupy most of the depth of the mucosa, and are lined with a single type of cell which has eosinophilic granules. Gut-associated lymphoid tissue (mainly lymphocytes, macrophages and eosinophilic granulocytes) is concentrated on the sides of the lamina muscularis mucosa and especially in the cores of the mucosal folds. The muscular coat consists of two or three layers entirely made up of smooth muscle cells.     

Ultrastructure of the copulatory stylet and accessory spines in Haplopharynx quadristimulus (Turbellaria)

The copulatory organ of Haplopharynx quadristimulus Ax, 1971 (Carolina form, Rieger, 1977) consists of a proximal prostatic vesicle and a distal stylet apparatus comprising a central tubular stylet and four to five peripheral accessory spines. By electron microscopy it could be seen that the stylet and spines were intracellular specializations. The copulatory organ can be interpreted as a specialization of an epithelial canal extending from the testes to the body wall. In the complex stylet apparatus, the epithelium was differentiated into six cell types. The stylet, which was formed in a matrix syncytium next to the prostatic vesicle, extended into the lumen of the stylet canal. The interior of the stylet apparatus contained one group of cells that had thick ciliary rootlets and another that had rootlet-like ribbons.The cells that contain the rootlets enveloped bundles of longitudinally arranged muscles. The accessory spines were formed in cells which lay peripheral to the muscle bundles. The spines, stylet, rootlet-like ribbons, and rootlets had similar patterns of periodic cross striations. The similarity in striation patterns suggests that the accessory spines and stylet are composed of modified ciliary rootlets.     

The system of epidermal ciliary rootlets in Turbellaria

Summary The rootlets of the kinetic cilia form patterns of different types in the different turbellarian subgroups (cf. Rieger 1981). In the Acoela a rather complex system of ciliary rootlets is found in the epidermis (Dorey 1965; Hendelberg & Hedlund 1973; Bedini & Papi 1974). In the acoel Childia groenlandica (Levinsen) the four rootlets of each cilium make contact with those of adjacent cilia at two levels (Hendelberg & Hedlund 1974). Distinct granules are found in the interior of the main rootlets (Hendelberg & Hedlund 1974; Bedini & Papi 1974, Fig. 16) and basal bodies (Silveira 1972; Hendelberg & Hedlund 1974) of the epidermal kinetic cilia of acoels. Similar granules, probably of identical structure, can be seen in nemertodermatids, in the same positions (Tyler & Rieger 1977, Figs. 3 & 6). Such granules were studied in C. groenlandica with histochemical methods adapted for electron microscopy. Like Silveira (1972) I found the granules of the basal bodies to be Thiéry-positive, and thus evidently to be made up of or at least to contain polysaccharide material. The granules of the main rootlets were also found to be Thiéry-positive (Hendelberg 1976). Digestion experiments (Hendelberg & Hellmén 1978 and unpublished results) strongly support the concept that the granules are glycogen beta-particles.We know that cilia can function as kinetic organelles without any rootlets. But we are still uncertain about the function of the rootlets when occurring. Most probably they form an anchorage, a function which may be favoured by branching rootlets making contact with each other. Another function which has been discussed is the transmittance of impulses regulating the ciliary beat. Glycogen granules represent an energy deposit. The functional implication of these granules in the interior of the ciliary rootlets and basal bodies is not clear. However, the observations raise the question of how energy is transmitted to the cilia. Are the ciliary rootlets, when occurring, involved? This question will be further discussed, with references, in a future full report on the digestion experiments (to be published elsewhere).     

An ultrastructural study of oogenesis in a marine triclad

The ultrastructural features of oocyte differentiation were studied in the marine triclad Cercyra hastata. Oocytes at several stages of maturation, each surrounded by follicle cell projections, are present within each of the two ovaries. A pre-vitellogenic and a vitellogenic stage have been detected in the oogenesis of C. hastata. The pre-vitellogenic stage is mainly characterized by an increase in the nuclear and nucleolar volume and activity, and the appearance and development of cortical granule precursors which are elaborated by the Golgi complex. In early phases of the vitellogenic stage, intense delamination and blebbing of the nuclear envelope occurs which probably contributes to an increase in number of cytoplasmic membranes and to transfer of nuclear material to the cytoplasm. The rough endoplasmic reticulum is extensively developed and often assumes a ‘whorl’ array. Several areas of yolk precursor formation appear in the whorls. Numerous 2–5 μm protein yolk globules are subsequently formed which appear surrounded by a double membrane (cisternae of the smooth endoplasmic reticulum) and become randomly distributed throughout the cytoplasm of mature oocytes. The peripheral ooplasm is occupied by a monolayer of electron-dense cortical granules. Finally, the evolutionary significance of the autosynthetic mechanism of yolk production is discussed.