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  • 1
    Electronic Resource
    Electronic Resource
    A comparative study on ciliary differentiation in the ascidian branchial stigmata
    Amsterdam : Elsevier
    Cell Biology International Reports 10 (1986), S. 171 
    Details
    ISSN: 0309-1651
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/S0309-1651(86)80025-X
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  • 2
    Electronic Resource
    Electronic Resource
    A comparative study on ciliary differentiation in the ascidian branchial stigmata
    Amsterdam : Elsevier
    Cell Biology International Reports 10 (1986), S. 171 
    Details
    ISSN: 0309-1651
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/S0309-1651(86)80025-X
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Muscle cell differentiation in the ascidian heart
    Amsterdam : Elsevier
    Developmental Biology 68 (1979), S. 371-380 
    Details
    ISSN: 0012-1606
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0012-1606(79)90211-2
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  • 4
    Electronic Resource
    Electronic Resource
    Sexual reproduction in the compound ascidian Diplosoma listerianum (Tunicata). II. Sperm penetration through ovary wall and evidence of internal fertilization (1994)
    Springer
    Marine biology 118 (1994), S. 499-510 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Diplosoma listerianum differs from most ascidians in that, at ovulation, eggs are emitted at the bottom of the ovary and segregated into the tunic, so that fertilization occurs far from seawater. A fertilization canal, a hollow extension of the ovary, conducts sperm towards the egg. In the present paper, ultrastructural evidence is reported on the morphological relationship between the ovary, egg envelopes and oocyte and on the mechanism by which sperm-egg interaction is established. In the ovary, the very complex sperm, equipped with a spiral “dense groove”, undergo metamorphosis as the first step in a sperm reaction and then pass through the ovary epithelium insinuating themselves between the intercellular junctions which appear to be mouldable, although able to maintain the egg-ovary barrier. Sperm then reach the vitelline coat, where a further step in the sperm reaction occurs. Before the egg abandons the ovary, the sperm head is incorporated into the oocyte by a process recalling phagocytosis, with the formation of an engulfing pocket. Sperm-egg contact and incorporation in D. listerianum occur in a way, never previously reported for other ascidians, in which fusion of plasma membranes takes place immediately after sperm-egg contact. Unlike other cytoplasmic components, the dense groove persists until the sperm enters the egg. It gives a corkscrew-like configuration to the sperm head and allows close adhesion to cell membranes, facilitating sperm movement. Expulsion of numerous cortical granules and features of a cortical reaction were observed in the egg penetrated by the sperm. The mode of internal fertilization of this species in comparison with that of other tunicates and phylogenetic aspects are discussed. Ripe colonies of D. listerianum collected in the Lagoon of Venice, Italy in 1986 and 1991 and colonies reared on glass in aquaria were used for our investigations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00350307
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  • 5
    Electronic Resource
    Electronic Resource
    Sexual reproduction in the compound ascidian Diplosoma listerianum (Tunicata). I. Metamorphosis, storage and phagocytosis of sperm in female duct (1994)
    Springer
    Marine biology 118 (1994), S. 489-498 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In the colonial ascidian Diplosoma listerianum (collected in the Lagoon of Venice in 1986 and 1991), ovulating eggs detach themselves from the ovary wall and segregate in the tunic without exposure to seawater. With the aim of finding evidence of the pathway followed by spermatozoa to approach the oocyte, histological and ultrastructural observations were made. The results showed that the hollow ovary elongates in a “fertilization canal” which flanks the sperm duct and opens externally, next to the anus. Intercellular extended tight junctions isolate the lumen of this canal from the blood. Sperm were found in the fertilization canal, both free and in intracellular vacuoles of wandering cells (phagocytes). These sperm showed differences in comparison to those from the sperm duct, which are possible signs of a sperm reaction. The main modifications were shown by the “dense groove”, a narrow invagination of the plasmalemma bound to the nuclear envelope by dense material. In non-modified sperm, the groove runs spirally all along the head, while in those in the fertilization canal, it coils in the anterior half of the head, pressing back the long mitochondrion and endoplasmic tubules. These modifications were interpreted to be result of the release of the dense groove, considered to be a sort of stretched, contractile spring. The presence of sperm in the fertilization canal and particularly in phagocytes is discussed in relation to the capacity for exogenous sperm storage by zooids and to the necessity of waste clearance in order for successive waves of fresh sperm to be able to move towards fully grown oocytes. The origin of the female fertilization canal, the role of its tight junctions, and the complex sperm morphology are discussed as adaptations to internal fertilization in D. listerianum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00350306
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  • 6
    Electronic Resource
    Electronic Resource
    Involution of the caudal musculature during metamorphosis in the ascidian, Botryllus schlosseri (1974)
    Springer
    Cell & tissue research 153 (1974), S. 293-305 
    Details
    ISSN: 1432-0878
    Keywords: Ascidia (Botryllus schlosseri) ; Metamorphosis ; Muscle tissue involution ; Phagocytes ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The caudal musculature of the free-swimming tadpole of the ascidian, B. schlosseri consists of cylindrical mononucleated cells connected in longitudinal rows flanking the axial notochord. During resorption of the larval tail, which is apparently induced by the contraction of the epidermis, muscle cells are dissociated and pushed into the body cavity where most of them are rapidly engulfed by phagocytes. In the initial stages of tail withdrawal muscle cells display surface alterations due to the disruption of intercellular junctions and disarrangement of myofibrils. Extensive degenerative changes, with shrinkage of mitochondria and disintegration of the contractile material are subsequently observed. Lysosomes and autophagic vacuoles are rarely seen and appear to play a secondary role in the degradation of the muscle cells, which occurs predominantly within the phagocytes. Myofilaments and myofibrils have never been observed within autophagic vacuoles. Clumps of muscle fragments and degenerated phagocytes undergo eventual dissolution in the blood lacunae, concomitantly with the differentiation of the young oozooid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00229160
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  • 7
    Electronic Resource
    Electronic Resource
    Degenerative regression of the digestive tract in the colonial ascidian Botryllus schlossen (Pallas) (1984)
    Springer
    Cell & tissue research 235 (1984), S. 309-318 
    Details
    ISSN: 1432-0878
    Keywords: Ascidian ; Gut ; Cell involution ; Ultrastructure ; Phagocytes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Degenerative changes in the digestive tract of zooids of Botryllus schlosseri were studied by light and electron microscopy. Three main processes occurred in the tissues: contraction, involution and phagocytosis. The contraction of epidermis and peribranchial epithelium in which cytoplasmic microfilaments probably participate, seemed to have a special role in compressing the underlying organs. During contraction most of the body cavities collapsed, the branchial walls disintegrated and the fragments were rapidly taken up by large phagocytes. The gut epithelium retained its apparent continuity longer, though isolated phagocytes infiltrated it to eliminate single cells. Cell degeneration came about chiefly either through swelling and lysis of cells or through loss of water and condensation of cytoplasm and nucleus. The fate of all regressed tissues was to be engulfed and digested by wandering phagocytes. However, it was also observed that numerous cells of different epithelia could act as fixed phagocytes by engulfing cell debris and entire cells into heterophagic vacuoles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00217855
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  • 8
    Electronic Resource
    Electronic Resource
    A comparative study of the organization of the sarcotubular system in ascidian musclePortions of this study were reported at the 1975 Congress of the Italian Society for Electron Microscopy, Ostuni, Bari, and have appeared in abstract (Burighel et al., 1976) (1977)
    New York, NY : Wiley-Blackwell
    Journal of Morphology 153 (1977), S. 205-223 
    Details
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The caudal musculature of ascidian tadpole larvae consists of mononucleated muscle cells joined end to end in long rows flanking the notochord. A comparative study of the fine structure of these cells in larvae from different families has revealed wide variations in the pattern of organization of the sarcotubular system. The species examined can be distinguished in two groups according to the presence or absence of a system of plasma membrane invaginations equivalent to the T system of vertebrate and invertebrate striated muscle. Muscle cells from the first group of species, Clavelina lepadiformis, Ciona intestinalis and Molgula socialis, are characterized by absence of T system and show peripheral couplings of sarcoplasmic reticulum cisternae directly with the plasma membrane. In contrast, a T system is present in muscle cells of Diplosoma listerianum, Styela plicata and Botrylloides leachi. The presence of T system in ascidian muscle is not related to the taxonomic position of the various species, but rather to the intracellular disposition of the myofibrils, which are peripheral in the species of the first group whereas they occupy a more internal position in the species of the second group.The T system displays unique structural features in ascidian muscle. It consists of wide laminae invaginating from the plasma membrane and associated in longitudinally oriented dyads with sarcoplasmic reticulum cisternae in register with the I band of the myofibrils. It is apparent from these observations that, in contrast with the uniformity of myofibrillar structure in all chordates, there are basic differences between ascidians and vertebrates as regards the organization of the sarcotubular system. On the other hand, there are significant similarities in this respect between ascidian and invertebrate muscle.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jmor.1051530204
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  • 9
    Electronic Resource
    Electronic Resource
    Junctional diversity in two regions of the epidermis of Oikopleura dioica (Tunicata, Larvacea) (1989)
    Springer
    Cell & tissue research 257 (1989), S. 529-535 
    Details
    ISSN: 1432-0878
    Keywords: Epidermis ; Epithelial cells ; Intermediate junctions ; Tight junctions ; Appendicularian, Oikopleuradioica (Tunicata)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary A simple continuous epithelium surrounds the body of the pelagic larvacean. It consists of two zones of cells: oikoplast cells and flattened cells. The oikoplast cells are columnar and produce a thick extracellular ‘house’ that ensheathes the body of the organism. These cells are joined laterally by wide tight junctions (zonulae occludentes). The tail of the animal is surrounded by exceedingly thin cells which are joined by narrow tight junctions under which lie intermediate junctions (zonulae adhaerentes) and gap junctions. A web of fibrous material inserts into the intermediate junctions. The transitional cells between the two epithelial zones have one lateral border with a wide tight junction, and the other lateral border with a narrow tight junction and a wide intermediate junction. In freeze-fracture replicas, the wide tight junction has a number of anastomosing ridges, in comparison with the narrow tight junction, which usually consists of only a single row of intramembranous particles. In replicas, the thin epithelial cells show unusual parallel arrays of particles in clusters on their apical plasma membranes. This simple epithelium, therefore, exhibits striking differences between the two cellular zones, in the structural characteristics of both the lateral borders and the apical membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00221462
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  • 10
    Electronic Resource
    Electronic Resource
    Junctional complexes of the branchia and gut of the tunicate, Pyrosoma atlanticum (Pyrosomatida, Thaliacea) (1992)
    Springer
    Cell & tissue research 267 (1992), S. 357-364 
    Details
    ISSN: 1432-0878
    Keywords: Branchial stigmata ; Gut ; Epithelium ; Cell junctions ; Pyrosomatida, Pyrosoma atlanticum (Tunicata)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The branchia of pyrosomes has been found to be like that of ascidians in that it shares with the latter, besides the presence of peribranchial chambers, stigmata bordered by clusters of seven rows of flattened cells, each bearing a single row of long cilia. The intercellular junctions between ciliated cells of the branchial basket and between the cells lining the gut, in pyrosomes, have been studied in thin sections and by freeze-fracture. In both tissues tight and gap junctions are present, but the former are much more extensive in the gut. The gap junctions in the branchial basket exhibit some atypical features. Moreover, although there are extensive zonulae adhaerentes between the ciliated cells of the branchial basket, there are none between the epithelial cells of the intestinal tract. This feature of the branchiae, together with the alignment of their cells into highly ordered rows of seven cells, are similar to those found in some groups of ascidians. The evolutionary relationships between pyrosomes and the aplousobranch ascidians are considered in the light of these results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00302974
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