腔肠动物平衡感觉器官结构的研究进展

本文概述了腔肠动物的平衡感觉器官结构：刺胞动物掌状伞形螅（Corymorpha palma）固着器末端的无纤毛平衡囊、软水母（Leptomedusae）钟形伞缘的开放型和封闭型平衡囊、筐水母（Narcomedusae）外伞表面外伞神经环上方边缘有感觉棍的间囊水母（Aegina）和有感觉乳突及感觉棍的嗜阳水母（Solmissus）的平衡囊、硬水母（Trachymedusae）外伞神经环上方边缘的平衡囊、钵水母（Scyphozoa）伞缘的感觉棍和立方水母（Cubozoa）伞缘稍上方的感觉棍,栉水母（Ctenophore）反口面中央的平衡囊或顶器官。本文内容对理解其他水生无脊椎动物的平衡感觉器官的结构及功能有重要意义,同时也可能作为对现行动物学相关教材内容的有益补充。     

ULTRASTRUCTURE DES STATOCYSTES CHEZ SCROBICULARIA PLANA ET TELLINA TENUIS (MOLLUSQUES LAMELLIBRANCHES TELLINACEA)

The statocysts of Scrobicularia plana and Tellina tenuis arecomposed of 8 sensory hair-cells separated by giant cells characterizedby a fibrous cytoskeleton. The sensory cells bear few ciliaespecially in S. plana. These cilia are responsible both forrotation of the statolith and for the transduction of stimuli.Their basal bodies bear a side rootlet facing a basal foot anda crown composed of 9 spokes. Such statocysts seem to receiveonly multidirectional stimuli and to allow a less diversifiedbehaviour than the statocysts of Pecten. (Received 16 September 1980;     

The ultrastructure of the statocysts in the pediveliger larvae of Pecten maximus (L.) (Bivalvia)

The pediveliger of Pecten maximus (L.) has a pair of statocysts situated at the base of the foot on either side of a bilobed pedal ganglion. The statocysts consist of a spherical sac connected to the mantle cavity by a cylindrical ciliated canal. Within the sac there are statoconia which are variable both in shape and structure. The cells of the sac are joined by septate desmosomes. There is a non-ciliated cell in each sac containing a variety of granules some of which resemble certain of the statoconia. The remainder of the sac is composed of hair cells, which bear a circular array of radiating cilia. The basal bodies and horizontal striated roots of these cilia are directed radially. The hair cells give rise to thin processes which probably join together to form the static nerve. This nerve runs from the static canal to the pleural ganglion.     

Stereoscan studies of eggs, free-swimming and penetrating miracidia and early sporocysts of Fasciola hepatica.

The egg of Fasciola hepatica has a smooth surface with a slightly elevated circle marking the fracture of the operculum. The operculum and the aperture have crenated edges. The epithelial cells of the miracidium are covered with long cilia. When miracidia are vibrated in an ultrasonic cleaner the cilia of the epithelial cells of the four posteroir tiers are broken off only leaving longitudinal rows of cilium stubs, whereas the cilia of the first tier are still retained. The apical papilla is provided with a dorso-ventral furrow, multiciliated pits and isolated sensory cilia. The narrow intercellular ridge is smooth, whereas the epithelial cells have small cytoplasmic knobs between the cilia. The penetration into the snail (Lymnaea truncatula) and the transforamtion into sporocyst may be separated into three phases. (1) Less than 1 min after attachment to the snail the ciliated cells of the anterior tier are shed and swim away. (2) The cilia of the remaining cells beat violently and after about 5 min most cilia are broken off near the cell surface. The miracidium remains for about 15 min embedded as far as the intracellular ridge receptors (lateral papillae and sheathed ciliated nerve endings). During this period extensive contraction and relaxation of the body are performed. (3) The final penetration of the snail epithelium takes about 15 min. Simultaneously with the penetration into the snail tissue the "bald" cells (epithelial cells with cilium stubs only) of the four posterior tiers loosen, florm globules and fall off. The surface below the cells is smooth and in cytoplasmic continuity with the intercellular ridge and the apical papilla, and this syncytium forms the later tegument of the sporocyst. After a few days the tegument of the sporocyst is provided with microvillus-like projections and the apical papilla and sensory structures are lost.     

Structure and Development of the Olfactory Organ in the Garfish Belone belone (L.) (Teleostei,Atheriniformes)

Theisen, B., Breucker, H., Zeiske, E., Melinkat, R. 1980. Structure and development of the olfactory organ in the garfish Belone belone (L.) (Teleostei, Atheriniformes). (Institute of Comparative Anatomy, University of Copenhagen, Denmark; Anatomisches Institut, Universität Hamburg, and Zoologisches Institut und Zoologisches Museum, Universität Hamburg, Federal Republic of Germany.) — Acta zool. (Stockh.) 61(3): 161–170. The structure and development of the olfactory organ in the garfish Belone belone (L.) were studied by light and electron microscopy (SEM and TEM). The olfactory organ has the shape of an open groove with a protruding papilla. In embryos and early juveniles the groove is smooth and is provided with a continuous sensory epithelium. During ontogenesis the papilla develops and the composition of the epithelium is changed as areas of nonsensory epithelium appear and eventually separate the sensory epithelium into islets. In adults the sensory epithelium consists of supporting, basal, and two types of receptor cells, ciliated and microvillous. In juveniles also ciliated nonsensory cells are present. This difference can be correlated with differing locomotory habits of adults and juveniles. The receptor cilia show a 9 + 0 microtubular pattern while the nonsensory cilia have the general 9 + 2 pattern. Deviating dendritic endings were found and are considered an indication of ongoing cell dynamics.     

Ultrastructure of the nuchal organ in the interstitial polychaete Stygocapitella subterranea (Parergodrilidae)

The nuchal organs of Stygocapitella subterranea are paired narrow pits. They are lined by unciliated cells at the opening and by ciliated cells at the basal parts. The primary sensory cells (6–8) are arranged in a single patch at the bottom of the nuchal pit. The nuclei of the sensory cells are located in the posterior portion of the brain. Their dendrites form the nuchal nerve which is sheathed by the ciliated cells. Each sensory cell bears up to 4 modified sensory cilia and several microvilli extending into the olfactory chamber. The sensory cilia show various patterns of axonemal organization and have no rootlets. The olfactory chamber is covered by a cuticular matrix. Another primary sensory cell lies at the opening of the nuchal pit. It bears cilia which penetrate the cuticle but are enveloped by the epicuticle. Retractor muscles insert caudally on the organ. The nuchal organ of S. subterranea shows similarities to those of opheliids but exhibits several features not to be found in other nuchal organs.     

Ultrastructural aspects of nervous-system and statocyst morphogenesis during embryonic development of Convoluta psammophila (Turbellaria,Acoela)

The notion that statocysts originated from an infolding of ectoderm lined by ciliated sensory cells has been challenged with evidence of capsule-limited, non-ciliary statocysts in several independent phyla. Statocysts in turbellarians primitively lack cilia and are embedded within or closely adjoined to the cerebral ganglion; they are likely to be derived from nervous tissue. We investigated the development of the simple statocyst in an acoel turbellarian, a statocyst consisting of three cells. Observations of serial TEM sections of embryos at different stages of development support the hypothesis of an inner (non-epithelial) origin of the statocyst. First, a three-cell complex is delimited by a basal lamina; it then undergoes cavitation by swelling, autophagy, and fluid secretion. The statocyst becomes discernible within the precursor ganglion cells while they still contain yolk inclusions. The two outer (parietal) cells, enclosed together by a 10-nm-thick basal lamina, arrange themselves in an ovoid of about 10 µm diameter and surround the inner statolith-forming cell. The statolith is formed later within vacuoles of the statolith-forming cell.     

Ultrastructure of the Statocysts in the Apodous Sea Cucumber Leptosynapta inhaerens (Holothuroidea, Echinodermata)

The burrowing sea cucumber Leptosynapta inhaerens possesses five pairs of statocysts, one pair on either side of each radial nerve cord where it arises from the circumoral nerve ring. The nerve cords exhibit only ectoneural components at the level of the statocysts. A sinus-like epineural canal lies superjacent to each cord. This canal is lined by a robust monociliated neuroepithelium which lacks any special support cells. Beneath the neuroepithelium, the somata of the ectoneural neurons form a perikaryal layer whereas the axons are located within the proximal parts of the cords. Glial cells have not been found. Each statocyst is a hollow sense organ. Its central cavity is lined by a monolayer of monociliated parietal cells. Axons of these parietal cells extend towards the statocyst nerve which connects each statocyst with the ectoneural pathways of the cord. A single lithocyte floats within each central statocyst cavity. This unciliated cell contains a voluminous vacuole with the statolith and several smaller vacuoles. It is concluded that statocysts do not belong to the basic organization of the Holothuroidea but have been evolved within this group. The statement, that the statocysts of apodous sea cucumbers and that of the enigmatic Xenoturbella bocki are homologous organs, is rejected.     

Intraflagellar transport is required in Drosophila to differentiate sensory cilia but not sperm

BACKGROUND: Intraflagellar transport (IFT) uses kinesin II to carry a multiprotein particle to the tips of eukaryotic cilia and flagella and a nonaxonemal dynein to return it to the cell body. IFT particle proteins and motors are conserved in ciliated eukaryotes, and IFT-deficient mutants in algae, nematodes, and mammals fail to extend or maintain cilia and flagella, including sensory cilia. In Drosophila, the only ciliated cells are sensory neurons and sperm. no mechanoreceptor potential (nomp) mutations have been isolated that affect the differentiation and function of ciliated sense organs. The nompB gene is here shown to encode an IFT protein. Its mutant phenotypes reveal the consequences of an IFT defect in an insect. RESULTS: Mechanosensory and olfactory neurons in nompB mutants have missing or defective cilia. nompB encodes the Drosophila homolog of the IFT complex B protein IFT88/Polaris/OSM-5. nompB is expressed in the ciliated sensory neurons, and a functional, tagged NOMPB protein is located in sensory cilia and around basal bodies. Surprisingly, nompB mutant males produce normally elongated, motile sperm. Neuronally restricted expression and male germline mosaic experiments show that nompB-deficient sperm are fully functional in transfer, competition, and fertilization. CONCLUSIONS: NOMPB, the Drosophila homolog of IFT88, is required for the assembly of sensory cilia but not for the extension or function of the sperm flagellum. Assembly of this extremely long axoneme is therefore independent of IFT.     

Hydromedusan distribution patterns

A possible ancient origin of the Anthomedusae, Leptomedusae and Limnomedusae in the Indo-Malayan region and of the Narcomedusae and Trachymedusae in the Antarctic region is postulated. Conclusions are based on recent distribution patterns and comparison with Euphausiacea distributions.     

Comparative morphology of statocysts in the Plathelminthes and the Xenoturbellida

The general fine-structural organization of statocysts in Catenulida, Nemertodermatida, Acoela, Proseriata, Lurus (Dalyellioida), and Xenoturbella are summarized. In lithophorous (statocyst-bearing) members of the Catenulida, the statocysts exhibit a few parietal cells and one or several movable statoliths within a spacious intracapsular cavity. Statocysts in the Nemertodermatida have several parietal cells and two lithocytes, each equipped with one statolith, whereas those of the other acoelomorphan taxon, the Acoela, always have two parietal cells and one movable lithocyte. The statocysts of lithophorous members of the Proseriata represent more sophisticated systems: each has two clusters of accessory cells in addition to several parietal cells and a voluminous lithocyte in which the statolith is movable. In catenulids and proseriates, processes of outer neurons penetrate the capsule of the statocyst, whereas such innervations have not been found in the Nemertodermatida and Acoela. I conclude that the different types of statocysts have evolved independently within the Plathelminthes. Xenoturbella displays an intraepidermal statocyst with many monociliary parietal cells and several mobile cells (lithocytes) within the central cavity of the statocyst. Each of these mobile cells carries a statolith-like structure and one prominent cilium. The statocyst of Xenoturbella does not correspond to any type of plathelminth statocyst.     

Organization of actin microfilaments in the apical border of oviduct ciliated cells

Actin microfilaments were localized in quail oviduct ciliated cells using decoration with myosin subfragment S1 and immunogold labeling. These polarized epithelial cells show a well developed cytoskeleton due to the presence of numerous cilia and microvilli at their apical pole. Most S1-decorated microfilaments extend from the microvilli downward towards the upper part of the ciliary striated rootlets with which they are connected. From the microvillous roots, a few microfilaments connect the proximal part of the basal body or the basal foot associated with the basal body. Microfilament polarity is shown by S1 arrowheads pointing away from the microvillous tip to the cell body. Furthermore, short microfilaments are attached to the plasma membrane at the anchoring sites of basal bodies and run along the basal body. The polarity of these short microfilaments is directed from the basal body anchoring fibers downward to the cytoplasm. At the cell periphery, microfilaments from microvillous roots and ciliary apparatus are connected with those of the circumferential actin belt which is associated with the apical zonula adhaerens. Together with the other cytoskeletal elements, the microfilaments increase ciliary anchorage and could be involved in the coordination of ciliary beating. Moreover, microvilli surrounding the cilia probably modify ciliary beating by offering resistance to cilium bending. The presence of microvilli could explain the fact that mainly the upper part of the cilia appanars to be involved in the axonemal bending in metazoan ciliated cells.     

Morphology and ultrastructure of the organ of Bellonci in the marine amphipod Gammarus setosus

The three-dimensional structure of the organ of Bellonci in the marine amphipod Gammarus setosus and the relationship between its sensory cells and concretion are described using light, transmission, and scanning electron microscopy, with chemical treatment for cell lysis, calcium chelation, glycogen staining, and lanthanum labelling. The organ is encapsulated and has three units called fuselli. Each is enclosed by two fusellar cells which generate and release calcium granule strands into the cores of the fusellar concretions, which are united in the center of the organ. The surface of each fusellus is traversed by spiral dendrites entering dorsally and ending ventrally. The spiral dendrites arise from sensory neurons contained in a palm-shaped ganglion in the center of the capsule, beyond which they are twisted like a rope before reaching the concretion. The spiral dendrites are linked in pairs by gap and tight junctions and each gives origin to two pairs of 9+0 sensory cilia 30 μm apart. The ciliary distal segments give rise to long tubules which are in contact with the calcium granule strands. The ciliary proximal segments are expanded by many long mitochondria which interdigitate with the branched striated ciliary rootlets. The concretion is suspended in the capsule cavity by axons originating from four neurons of a remote mechanoreceptor. The structure of the organ suggests that it is a sensory organ involved in the reception and integration of a variety of stimuli.     

Fine structural study of the statocysts in the veliger larva of the nudibranch,Rostanga pulchra

Summary The two statocysts of the veliger larva of Rostanga pulchra are positioned within the base of the foot. They are spherical, fluid-filled capsule that contain a large, calcareous statolith and several smaller concretions. The epithelium of the statocyst is composed of 10 ciliated sensory cells (hair cells) and 11 accessory cells. The latter group stains darkly and includes 2 microvillous cells, 7 supporting cells, and 2 glial cells. The hair cells stain lightly and each gives rise to an axon; two types can be distinguished. The first type, in which a minimum of 3 cilia are randomly positioned on the apical cell membrane, is restricted to the upper portion of the statocyst. The second type, in which 9 to 11 cilia are arranged in a slightly curved row, is found exclusively around the base of the statocyst. Each statocyst is connected dorso-laterally to the ipsilateral cerebral ganglion by a short static nerve, formed by axons arising from the hair cells. Ganglionic neurons synapse with these axons as the static nerve enters the cerebral ganglion. The lumen of the statocyst is continuous with a blind constricted canal located beneath the static nerve.A diagram showing the structure of the statocyst and its association with the nervous system is presented. Possible functions of the statocyst in relation to larval behavior are discussed.     

COMPARISON OF THE STRUCTURE OF THE PALLIAL TENTACLES OF SEVEN SPECIES OF SOUTH AFRICAN PATELLID LIMPET

The ultrastructure of the pallial tentacles of seven speciesof patellid limpet is described. The tip of most of the tentaclesexamined bears a crown of long cilia, whereas the shaft of thetentacles has small tufts (5–10 µm diameter) ofshorter cilia. Sections through the ciliated tufts show themto be composed of several cells, each bearing cilia. The ciliacontain 5–7 central microtubules and therefore do nothave the conventional 9 + 2 arrangement of microtubules. Nerveprocesses run from the base of each ciliated cell to a nervebundle in the centre of the tentacle, suggesting a sensory function.Estimates of densities of ciliated tufts suggest that the territoriallimpets (Patella cochlear and P. longicosta) have the greaternumber of tufts. Electron dense plate-like structures are foundin the centre of the pallial tentacles of Patella cochlear,P. longicosta, P. granularis, P. barbara and Helcion pruinosus.Each plate is about 0.2 µm wide and is surrounded by adouble membrane. It is suggested that these may play a rolein scattering or reflecting light and thus form part of thedermal light sensing ability of these animals. (Received 26 January 1987;     

Fine structure of the cephalic sensory organ in veliger larvae of Littorina littorea, (L.) (Mesogastropoda,Littorinidae)

The cephalic sensory organ (CSO) in planktonic veliger larvae of Littorina littorea is situated dorsally between the velar lobes at the level of the shell aperture. It consists of ciliated primary sensory cells, adjacent accessory cells and supporting epithelial cells. Cell bodies of the ciliated cells originate in the cerebral commissure and their dendrites pass to the epidermis. The flask-shaped sensory cells are characterized by a deep invaginated lumen with modified cilia arising from the cell surface in the lumen. These cilia are presumed to be non-motile because they lack striated rootlets and show a modified microtubular pattern (6 + 2, 7 + 2 and 8 + 2). The adjacent accessory cells never possess an invaginated lumen; occasionally cilia and branched microvilli arise from the apical surface. These cells may be sensory, but there is no obvious direct connection with the nervous system. The supporting epithelial cells are part of the epidermis and flank the apical necks of the sensory and accessory cells. Morphological evidence suggests that the CSO may function in chemoreception related to substrate selection at settlement, feeding or other behaviour.     

Ultrastructure of the tubular nephron of the lizard Podarcis (= Lacerta) Taurica

The proximal, intermediate, and distal convoluted tubules of the neprhon of Podarcis (= Lacerta) taurica were examined by electron microscopy. Proximal tubule cells have large, apical cytoplasmic protrusions and microvilli interpreted to function in urate secretion. Adjacent cells are bound apically by tight junctions and desmosomes but interdigitate in their basal region. This situation is repeated in the other tubules with significant differences in intercellular space width. The basal surfaces bear numerous cytoplasmic processes. The intermediate tubule has proximal and distal segments each with dark, ciliated, and light cells, the cuboidal dark cells with dense cytoplasm constituting the main bulk of the wall. As the cells of the proximal and distal segments resemble those of the proximal and distal convoluted tubules, respectively, the intermediate tubule is considered as a transition region. The ciliated cell body has two broad processes extending from the lumen, one to the basement membrane and one to a foot process of a light cell. The light cell is surrounded by dark and ciliated cells. It does not reach the lumen, but contacts the basement membrane through a process running below a ciliated cell to form a mushroom-shaped structure in tubule cross-section, the light cell process forming the stalk and a ciliated cell the cap. The cilia probably propel the glomerular filtrate towards the distal convoluted tubule. This latter tubule has initial, middle, and terminal zones, all nonciliated but with different lumen widths and cell shapes.     

Cilia-lacking respiratory cells in ciliary aplasia

This report describes the ultrastructural alterations observed in the nasal and bronchial mucosa of an 11-yr-old male suffering from immotile cilia syndrome (ICS). The morphological features observed in this patient are consistent with a ciliary aplasia. In fact, ciliated cells appeared to be replaced by columnar cells lacking cilia and basal bodies, and bearing on their surface cilium-like projections without any internal axonemal structure. In spite of the absence of basal bodies, centrioles, and kinocilia, these cells unexpectedly showed mature striated roots and centriolar precursor material scattered throughout the apical cytoplasm. These data suggest that control over basal body assembly is distinct from control over striated root formation. The presence of the above-reported structures in cells otherwise presenting many morphological features of normal ciliated cells is discussed on the basis of current knowledge of respiratory cilia biogenesis.     

Ultrastructure of sensory cells on the mantle tentacles of the gastropod Notoacmea scutum

Previous studies have indicated that the mantle margin of the gastropod mollusc Notoacmea scutum is sensitive to chemical, photic, and mechanical stimulation. Here, the ultrastructure of sensory cells on the mantle tentacles of N. scutum is examined by transmission electron microscopy to determine if morphological types of sensory cells can be correlated with known sensory capabilities. The sensory cells of the mantle tentacles are found to be ciliated, primary receptors with subepithelial nuclei. The ciliated sensory endings are concentrated at the tip of the tentacles, but also occur in smaller numbers along the shaft. Ultrastructural differences between cilia form the basis of distinguishing two types of sensory ending. Type 1 sensory endings, which are over 90% of the endings, bar unusual cilia that typically are filled with an electron-dense material. Type 2 sensory endings bear cilia that have a 9 + 2 arrangement of longitudinal elements and thus more closely resemble previously reported sensory cilia of molluscs.