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Diagram of a fragment of a transverse section through the nephridium wall of Thysanocardia nigra in the area between the excretory sac and excretory tube.
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The microscopic anatomy and ultrastructure of nephridium have been studied in the sipunculan Thysanocardia nigra Ikeda, 1904 (Sipuncula, Sipunculidea) from the Sea of Japan using histological and electron microscopic techniques (SEM and TEM). This paper describes ultrastructural features of nephridial epithelium, muscle grid, and coelomic epitheliu...
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... the lumens of infoldings into the lumen of the nephridium and, at the same time, prohibits the reverse flux of fil- trate from the lumen of the nephridium into the lumens of the infoldings. The muscle cells are spindle-shaped; their nuclei and organelles are located in lateral sarco- plasmic sacs that occur as bulges of sarcoplasmic mem- brane (Figs. 5-6). From the side of the coelom, the sur- face of the excretory tube is lines with flattened podocytes; no multiciliary coelomic cells have been found there (Figs. 3-4, ...
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... or club-shaped apical parts of the colum- nar cells of excretory bunches freely extend into the lumen of the nephridium (Figs. 5-6). The cells are not directly attached to each other, and there are fine canals lined with microvilli and cilia between the cells (Figs. 5-6). Some of the canals run almost up to the basal part of the cells. The latter comprises a system of thin podocytary processes, the so-called basal labyrinth (Figs. 5-6). The apical surfaces of most ...
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... or club-shaped apical parts of the colum- nar cells of excretory bunches freely extend into the lumen of the nephridium (Figs. 5-6). The cells are not directly attached to each other, and there are fine canals lined with microvilli and cilia between the cells (Figs. 5-6). Some of the canals run almost up to the basal part of the cells. The latter comprises a system of thin podocytary processes, the so-called basal labyrinth (Figs. 5-6). The apical surfaces of most cells are almost naked, and sometimes they have infrequently scattered microvilli and isolated cilia (Figs. 5-6, 7a). On the sur- face of ...
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... extend into the lumen of the nephridium (Figs. 5-6). The cells are not directly attached to each other, and there are fine canals lined with microvilli and cilia between the cells (Figs. 5-6). Some of the canals run almost up to the basal part of the cells. The latter comprises a system of thin podocytary processes, the so-called basal labyrinth (Figs. 5-6). The apical surfaces of most cells are almost naked, and sometimes they have infrequently scattered microvilli and isolated cilia (Figs. 5-6, 7a). On the sur- face of some cells there are pits and characteristic microtubercles, which might be evidence of pinocyto- sis activity (Figs. 5-6). Large vesicles with electron- light content ...
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... microvilli and cilia between the cells (Figs. 5-6). Some of the canals run almost up to the basal part of the cells. The latter comprises a system of thin podocytary processes, the so-called basal labyrinth (Figs. 5-6). The apical surfaces of most cells are almost naked, and sometimes they have infrequently scattered microvilli and isolated cilia (Figs. 5-6, 7a). On the sur- face of some cells there are pits and characteristic microtubercles, which might be evidence of pinocyto- sis activity (Figs. 5-6). Large vesicles with electron- light content can arise from the apical surfaces of some cells (Figs. 5-6, 7a). These vesicles commonly origi- nate from the entire apical parts of columnar ...
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... thin podocytary processes, the so-called basal labyrinth (Figs. 5-6). The apical surfaces of most cells are almost naked, and sometimes they have infrequently scattered microvilli and isolated cilia (Figs. 5-6, 7a). On the sur- face of some cells there are pits and characteristic microtubercles, which might be evidence of pinocyto- sis activity (Figs. 5-6). Large vesicles with electron- light content can arise from the apical surfaces of some cells (Figs. 5-6, 7a). These vesicles commonly origi- nate from the entire apical parts of columnar cells, which indicates a merocrine secretion pattern (Figs. 5- 6, 7a). The apical cytoplasm of these cells is filled with vesicles of different ...
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... are almost naked, and sometimes they have infrequently scattered microvilli and isolated cilia (Figs. 5-6, 7a). On the sur- face of some cells there are pits and characteristic microtubercles, which might be evidence of pinocyto- sis activity (Figs. 5-6). Large vesicles with electron- light content can arise from the apical surfaces of some cells (Figs. 5-6, 7a). These vesicles commonly origi- nate from the entire apical parts of columnar cells, which indicates a merocrine secretion pattern (Figs. 5- 6, 7a). The apical cytoplasm of these cells is filled with vesicles of different sizes with electron-light content (Figs. 5-6). The central cytoplasm is filled with numer- ous granules with ...
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... electron- light content can arise from the apical surfaces of some cells (Figs. 5-6, 7a). These vesicles commonly origi- nate from the entire apical parts of columnar cells, which indicates a merocrine secretion pattern (Figs. 5- 6, 7a). The apical cytoplasm of these cells is filled with vesicles of different sizes with electron-light content (Figs. 5-6). The central cytoplasm is filled with numer- ous granules with different electron densities. The cyto- plasm also comprises the cisterns of the endoplasmic reticulum (ER) and the Golgi apparatus (GA) (Figs. 5- 6). It is possible to distinguish several types of these granules, whose sizes range from 0.75 to 2 µ m: (1) electron-dense ...
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... to distinguish several types of these granules, whose sizes range from 0.75 to 2 µ m: (1) electron-dense osmiophilic granules with concen- tric structures; (2) loose osmiophilic granules; (3) elec- tron-light granules with electron-dense osmiophilic peripheries; and (4) granules with electron-dense osmi- ophilic centers and bright peripheries (Figs. 5-6). In all likelihood, these types represent different maturation phases of the secretory granules. The nuclei of colum- nar cells are large with well pronounced central nucle- oli that are displaced toward the basal pole (Figs. 5-6). Slitlike spaces between the basal processes are filled with extracellular matrix (Figs. 5-6). The ...
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... osmiophilic peripheries; and (4) granules with electron-dense osmi- ophilic centers and bright peripheries (Figs. 5-6). In all likelihood, these types represent different maturation phases of the secretory granules. The nuclei of colum- nar cells are large with well pronounced central nucle- oli that are displaced toward the basal pole (Figs. 5-6). Slitlike spaces between the basal processes are filled with extracellular matrix (Figs. 5-6). The cytoplasm of cells in the zone of the basal labyrinth is filled with numerous mitochondria (Figs. 5-6). This labyrinth structure and such aggregations of mitochondria are characteristic of epithelial tissues, which have been ...
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... and bright peripheries (Figs. 5-6). In all likelihood, these types represent different maturation phases of the secretory granules. The nuclei of colum- nar cells are large with well pronounced central nucle- oli that are displaced toward the basal pole (Figs. 5-6). Slitlike spaces between the basal processes are filled with extracellular matrix (Figs. 5-6). The cytoplasm of cells in the zone of the basal labyrinth is filled with numerous mitochondria (Figs. 5-6). This labyrinth structure and such aggregations of mitochondria are characteristic of epithelial tissues, which have been experimentally shown to have active ion transport (see Berrige and Oschman ...
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... the secretory granules. The nuclei of colum- nar cells are large with well pronounced central nucle- oli that are displaced toward the basal pole (Figs. 5-6). Slitlike spaces between the basal processes are filled with extracellular matrix (Figs. 5-6). The cytoplasm of cells in the zone of the basal labyrinth is filled with numerous mitochondria (Figs. 5-6). This labyrinth structure and such aggregations of mitochondria are characteristic of epithelial tissues, which have been experimentally shown to have active ion transport (see Berrige and Oschman ...
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... apical cell surfaces of flask-shaped infoldings bear numerous microvilli and cilia, while slitlike spaces between the cells make up a system of thin microvillary canals running up to the border with the thin extracel- lular matrix (Figs. 5-6). In some canals there are single scattered cilia (Figs. 5-6). The cilia are anchored by two rootlets, one of which is very longwhile the other is very shortand arises from the basal body at an angle of 115 ° to the axis of the long rootlet (Fig. 8a). Cells con- tacts ( zonula adhaerens ) are located close to the apical surfaces of the ...
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... apical cell surfaces of flask-shaped infoldings bear numerous microvilli and cilia, while slitlike spaces between the cells make up a system of thin microvillary canals running up to the border with the thin extracel- lular matrix (Figs. 5-6). In some canals there are single scattered cilia (Figs. 5-6). The cilia are anchored by two rootlets, one of which is very longwhile the other is very shortand arises from the basal body at an angle of 115 ° to the axis of the long rootlet (Fig. 8a). Cells con- tacts ( zonula adhaerens ) are located close to the apical surfaces of the cells. The apical cytoplasm contains many small vesicles ...
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... surfaces of the cells in the flask-shaped infoldings, are also noteworthy (Figs. 7c, 7d). It is interesting that such vesicles occur also outside of the basal surface of the cells directly in the underlining of the extracellular matrix (Fig. 7d). On the surface of the excretory sac, the matrix layer is relatively thick and contains granulo- cytes (Fig. 5), whereas this layer on the excretory tube is thin and no granulocytes have been found in the latter case (Fig. 6). From the outside, the surface of the excretory sac is covered with a solid layer of the coelomic epithelium consisting of two cell types, multiciliary cells and branched flattened cells, that have no microvilli and cilia ...
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... layer on the excretory tube is thin and no granulocytes have been found in the latter case (Fig. 6). From the outside, the surface of the excretory sac is covered with a solid layer of the coelomic epithelium consisting of two cell types, multiciliary cells and branched flattened cells, that have no microvilli and cilia and are called "podocytes" (Fig. 5). The long pro- cesses of neighboring podocytes can freely overlap each other and cellular contacts are rare. Particular cell contacts, double diaphragms, have been noted between some processes. They are delicate bridges of extracel- lular material similar to a mucopolysaccharide layer on cell membranes (Fig. 7f). The presence of these ...
Citations
... Despite a thorough literature search (starting from comprehensive studies like Ruppert andSmith, 1988 andQuast, 2005), we could not find clear evidence for the presence of reabsorptive cells in the efferent nephridial portions of other invertebrates. The most similar structures were found in the metanephridial wall cells of Sipuncula, from which distinct basal surface enlargements have been reported (Serrano et al., 1993;Adrianov et al., 2002). Tube portions with similar cytological characteristics in epithelial cells have also been reported for polychaetes (Bartolomaeus, 1989b) and nemertines (Jespersen and Lü tzen, 1987). ...
A single pair of protonephridia is the typical larval excretory organ of molluscs. Their presence in postlarval developmental stages was discovered only recently. We found that the protonephridia of the polyplacophoran mollusc, Lepidochitona corrugata, achieve their most elaborate differentiation and become largest during the postlarval period. This study describes the protonephridia of L. corrugata using light and electron microscopy and interactive three-dimensional visualization. We focus on the postlarval developmental period, in which the protonephridia consist of three parts: the terminal part with the ultrafiltration sites at the distal end, the voluminous protonephridial kidney, and the efferent nephroduct leading to the nephropore. The ultrafiltration sites show filtration slits between regularly arranged thin pedicles. The ciliary flame originates from both the terminal cell and the duct cells of the terminal portion. The efferent duct also shows ciliation. The most conspicuous structures, the protonephridial kidneys, are voluminous swellings composed of reabsorptive cells ("nephrocytes"). These cells exhibit strong vacuolization and an infolding system increasing the basal surface. The protonephridial kidneys, previously not reported at such a level of organization in molluscs, strikingly resemble (metanephridial) kidneys of adult molluscan excretory systems.
... There is no blood vessel with podocytes as in other types of metanephridia (see Ruppert and Smith,'88). The coelomic wall of the nephridial sac shows areas with cells with podocytes covering a thick extracellular matrix and other areas with a thin matrix, but the cells on the nephridial side of the wall are all thick with a very complex cell membrane abutting the matrix (Rice, '93;Adrianov et al., 2002). ...
The embryology of sipunculans, entoprocts, nemertines, platyhelminths (excluding acoelomorphs), rotifers, ectoprocts, phoronids, brachiopods, echinoderms and enteropneusts is reviewed with special emphasis on cell-lineage and differentiation of ectodermal structures. A group Spiralia comprising the four first-mentioned phyla plus annelids and molluscs seems well defined through the presence of spiral cleavage with early blastomere specification, prototroch with characteristic cell-lineage, cerebral ganglia developing from cells of the first micromere quartet (i.e., the episphere) and a ventral nervous system developing from the hyposphere. The planktotrophic trochophore was probably the larval type of the ancestor of this group. Another group comprising phoronids, brachiopods, echinoderms and enteropneusts appears equally well delimited. It is characterized by radial cleavage with late blastomere specification, possibly by the presence of a neotroch consisting of monociliate cells, by the absence of cerebral ganglia and of a well-defined brain and paired longitudinal nerve cords developing in connection with the blastopore, and by coelomic organization. Its ancestral larval type was probably a dipleurula. Several characters link rotifers with the spiralians, although they do not show the spiral pattern in the cleavage. Ectoprocts are still a problematic group, but some characters indicate spiralian affinities.
... The sipunculan tentacles function in food collection and as a gas exchange organ [1,2,4,[12][13][14]. ...
The ultrastructure of the tentacles was studied in the sipunculid worm Thysanocardia nigra. Flexible digitate tentacles are arranged into the dorsal and ventral tentacular crowns at the anterior end of the introvert of Th. nigra. The tentacle bears oral, lateral, and aboral rows of cilia; on the oral side, there is a longitudinal groove. Each tentacle contains two oral tentacular canals and an aboral tentacular canal. The oral side of the tentacle is covered by a simple columnar epithelium, which contains large glandular cells that secrete their products onto the apical surface of the epithelium. The lateral and aboral epithelia are composed of cuboidal and flattened cells. The tentacular canals are lined with a flattened coelomic epithelium that consists of podocytes with their processes and multiciliated cells. The tentacular canals are continuous with the radial coelomic canals of the head and constitute the terminal parts of the tentacular coelom, which shows a highly complex morphology. Five tentacular nerves and circular and longitudinal muscle bands lie in the connective tissue of the tentacle wall. Similarities and differences in the tentacle morphology between Th. nigra and other sipunculan species are discussed.
Fine morphology of the tentacular apparatus of the sipunculan Thysanocardia nigra
Ikeda, 1904 was conducted as a part of a larger study of microscopic anatomy in the species. The
tentacular apparatus is composed of two rings of tentacles, the dorsal and oral crowns. The dorsal,
or nuchal, crown consists of an arc of nuchal tentacles dorsally enclosing the heart -shaped nuchal
organ. The oral disk carries numerous peripheral tentacles arranged in oral crown surrounding the
mouth. Peripheral tentacles are arranged in paired rows, additional tentacles being developed
posteriorly so as to form a radial series of U -shaped festoons. The parallel festoons extend down
the oral disk and run alongside the spherical head. New pairs of festoons appear at the base of the
nuchal crown. The tentacles are heart-shaped in cross section, the oral surface being widest. The
nuchal tentacles face the oral disk by the oral surface while the peripheral, or oral, tentacles are
twisted at the base at nearly right angles, so to face a ciliary groove of the corresponding festoon.
The central groove of festoon is composed of a median ridge bordered by longitudinal lateral
ridges with long cilia. The oral surface of tentacles is constructed of a multiciliated,
pseudostratified, columna! epithelium with some intraepidermal mucous cells. There are three
longitudinal tentacular canals lined by peritoneum. Hemerythrocytes flow through the lumen of
the canals. Tentacles and grooves of festoons form a filtering system upon which food particles
can be trapped. The filtering apparatus of Thysanocardia shows remarkable similarities with a
filtering system of sabellid polychaetes.
The microscopic anatomy and ultrastructure of the contractile vessel of the sipunculan Themiste hexadactyla (Satô, 1930) from Vostok Bay (the Sea of Japan) were studied by histological and electron microscope methods. The ultrastructural features of the internal (endothelium) and external (coelothelium) lining of the contractile vessel are described and illustrated. Numerous macromolecular filters, the so-called “double diaphragms,” were found in the external coelothelium facing the cavity of the trunk coelom. This suggests a possible filtration from the tentacular coelom into the trunk coelom though the contractile vessel wall. The microscopic peculiarities of the main tube of the contractile vessel and its numerous lateral branches twining around several internal organs are described in detail. The contractile vessel is polyfunctional: it can act as the main reservoir for the cavity fluid during the withdrawal of the tentacular crown and performs the functions of the distribution system in sipunculans.
In this study, we investigated fertilization cytology in Phascolosoma esculenta. The sperm binds to the oocyte envelope in a random position at the point of initial contact. An acrosomal reaction then occurs and the acrosomal filament penetrates the oocyte envelope. The apex of the acrosomal filament contacts with the plasma membrane of the oocyte at the point where the fertilization cone is formed. The fertilization cone then retracts, towing the acrosomal filament back and drawing the sperm into the oocyte. Subsequently, the pores on the oocyte envelope are blocked and filled with fibrin and colloid. After the oocyte is activated by sperm, the first and second meiosis processes start sequentially, followed by the release of the first and second polar bodies. After the second polar body is extruded, the haploid female nucleus rapidly reorganizes to form a female pronucleus. In comparison, the sperm nucleus begins to decondense and dilate after the first polar body is released. The male pronucleus is not formed until the end of the second meiosis. The male and female pronuclei migrate to the centre of the oosperm and are incorporated into the zygote nucleus and then the first cleavage occurs. A two cell embryo is then formed by plasma membrane invagination. The cytological changes of sperm and oocyte nuclei during sperm entry into the oocyte and the fertilization process in P. esculenta are characterized by: (1) the mature oocyte with fertilization ability being in the metaphase of the first meiosis; (2) sperm is drawn into the oocyte by the acrosomal filament and fertilization cone; (3) some abnormal phenomena such as polyspermy, multiple pronuclei and multipolar spindle; and (4) the male pronucleus is formed earlier than the female pronucleus, at which point they will fuse to form a zygote nucleus.
Ultrastructural characteristics of spermiogenesis in the peanut worm, Phascolosoma esculenta (Phascolosomatidea), were observed by transmission electron microscopy (TEM). The spermiogenesis principally occurs in the coelom and can be divided into three stages (the early, middle and late stages) based on the chromatin morphology, acrosome development, spermatozoon midpiece and flagellum formation. Spermatids within a given spermatid mass develop synchronously. With the spermiogenesis proceeding, the spermatid masses become loosely structured, and later, adjacent spermatids are interconnected at one extremity of the cells. Gradually, condensation of the chromatin accelerates and is almost completed in late spermiogenesis, leaving the late spermatids with highly condensed homogeneous chromatin. In the spermatid head, the conical acrosome is generally composed of an acrosomal vesicle which is formed by the coalescence of small proacrosomal vesicles within the cytoplasm, a subacrosomal space that situates between the acrosomal vesicle and nucleus, and an acrosomal rod which develops from a bunch of filamentous material within the subacrosomal space. Certain mitochondria move posteriorly towards the nucleus, thus constituting the spermatozoon midpiece. The flagellum, originated from the distal centriole, appears in the early spermiogenesis. Ultimately, mature spermatidium dissociates into numerous spermatozoa, which are subsequently released as a single cell from the coelom into the nephridia. The spermatozoon has a prominent head, containing an acrosome and nucleus, a short midpiece and a slender tail. When compared with other sipunculans or invertebrates with external fertilization, the spermiogenesis of P. esculenta, presumably, is closely associated with its biological adaptations for the reproductive strategy.
The microscopic anatomy and ultrastructure of the nephridia of the sipunculan Themiste hexadactyla (Satô, 1930) from the Sea of Japan were studied by the histological and electron microscopic methods. The fine structures of the ciliary funnel, muscular “tongue,” excretory sac, and excretory tube of the nephridium were described. The ultrastructural features of the excretory epithelium, cupola-shaped epithelial infoldings, excretory canals, and muscular layer in the extracellular matrix of the nephridial wall were examined and described in detail. The ultrastructure of the nephridial coelomic epithelium composed of podocytes with long processes and multiciliary cells was also examined and illustrated. Characteristic cell contacts between the processes of podocytes, viz., paired “double diaphragms,” were described and illustrated for the first time.
Light spectrum plays a key role in the biology of symbiotic corals, with blue light resulting in higher coral growth, zooxanthellae density, chlorophyll a content and photosynthesis rates as compared to red light. However, it is still unclear whether these physiological processes are blue-enhanced or red-repressed. This study investigated the individual and combined effects of blue and red light on the health, zooxanthellae density, photophysiology and colouration of the scleractinian coral Stylophora pistillata over 6 weeks. Coral fragments were exposed to blue, red, and combined 50/50% blue red light, at two irradiance levels (128 and 256 μmol m-2 s-1). Light spectrum affected the health/survival, zooxanthellae density, and NDVI (a proxy for chlorophyll a content) of S. pistillata. Blue light resulted in highest survival rates, whereas red light resulted in low survival at 256 μmol m-2 s-1. Blue light also resulted in higher zooxanthellae densities compared to red light at 256 μmol m-2 s-1, and a higher NDVI compared to red and combined blue red light. Overall, our results suggest that red light negatively affects the health, survival, symbiont density and NDVI of S. pistillata, with a dominance of red over blue light for NDVI.
Free-floating coelomocytes in the tentacular coelomic cavity of the sipunculan Thysanocardia nigra Ikeda, 1904, were studied using light interference contrast microscopy and scanning and transmission electron microscopy. The following coelomocyte types were distinguished: hemerythrocytes, amoebocytes, and two morphological types of granular cells. No clusters of specialized cells that had been reported to occur in the trunk coelom of Th. nigra were found in the tentacular coelom. The corresponding types of coelomocytes from the tentacular and trunk coelomic cavities were shown to differ in size. These two coeloms are completely separated in sipunculans.
