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1.
 The epidermis, rhabditic glands and receptors of the commensal flatworm Temnocephala minor are described using electron microscopic techniques. The epidermis is syncytial and non-ciliated at the anterior body end; it bears folds, microvilli and other structures which differ according to the body side. The nuclei are located intraepithelially and distally from the basal membrane. Long cilia occur at the posterior end anteriorly from the sucker. All receptor structures described belong to a single morphological type and stand in groups arising from epidermal pits. On the tentacles these groups are regularly distributed. Each receptor has a single cilium and a long rootlet. More than 15 000 receptors of this type have been estimated to occur on the surface of a single medium-sized specimen of T. minor. Although the total number of receptor structures appears very high, the number of different receptor types is extremely low in comparison to other taxa of flatworms. Accepted: 8 July 1997  相似文献   

2.
Summary The ultrastructure of a uniciliate and a quadruciliate receptor in the anterior end of the larva of Austramphilina elongata is described on the basis of serial sections. The uniciliate receptor has numerous branched and interconnected microvilli at its surface, several rings forming the electron dense collar, and cross-striated rootlets diverging from the basal body of the cilium. The quadruciliate receptor has four short club-shaped sensory cilia and a single electron-dense collar.Abbreviations used in figures ec electron-dense collar - ep epidermis - m microvilli - nt neurotubules - pe process of electron-dense collar - r rootlet of cilium - sc sensory cilium - sd septate desmosome  相似文献   

3.
Light microscopy of live or silver-impregnated specimens of the fish parasite Ichthyophthirius multifiliis show that the tomites are elongated and claviform with the anterior end broad. The cytostome, indicated by the presence of the organelle of Lieberkühn, is found in the lower part of the broadened anterior third of the tomite. The tapered posterior end bears a rigid, caudal cilium at its pole. Scanning electron microscopy reveals the caudal cilium and associated structures, including the depression from which the cilium protrudes, circumciliary ring, and raised struts on the ring. From these observations it is concluded that a previously reported “apical filament” found on the tomite is actually the posterior caudal cilium described by Canella & Rocchi-Canella in 1976.  相似文献   

4.
The cercaria of Austrobilharzia sp. from the marine prosobranch gastropod Planaxis sulcatus in Kuwait Bay is described. The surface microtopography and pattern of the tegumentary sensory receptors are examined using scanning electron microscopy. The general microtopography of the surface of the cercaria is similar to that previously observed in cercariae of mammalian schistosomes, although differences are recorded in the types, numbers and distribution of the sensory receptors. The study identified more than 13 types of receptors comprising aciliated, uniciliated and for the first time a multiciliated receptor in a strigeid cercaria. The ciliated receptor types differ in the cilium length and structure of the surrounding collar and tegumentary base. The receptor types are site specific: (1) the aciliated and pitlike on the anterior organ-neck region and ventral sucker; (2) the uniciliated with a long flexible cilium with or without collar or a tegumentary base on the body and tail; and (3) the uniciliated with a short rigid cilium and a robust collar and tegumentary base, and the multiciliated with 6 flexible cilia and a high cylindrical collar on the anterior organ tip. The reported SEM information on the sensory receptors may contribute to elucidating their functional role and to establishing morphological characters for the phylogeny of the family Schistosomatidae.  相似文献   

5.
The Korean shuttles mudskipper Periophthalmus modestus has paired olfactory organs on its snout, consisting of anterior and posterior nostrils, a single olfactory canal with sensory and nonsensory epithelia, and a single accessory nasal sac. Its sensory epithelium consists of numerous islets forming a pseudostratified layer and contains various cells: olfactory receptor neurons, supporting cells, basal cells, lymphatic cells (LCs), and axon bundles. The sensory epithelium is a stratified squamous layer comprising stratified epithelial cells, mucous cells (MCs) with glycogen, flattened cells (FCs), LCs, and unidentified cells. Specific structures are as follows: (a) a tubular anterior nostril projecting outward, (b) a slit posterior nostril, (c) an elongated olfactory canal, (d) an ethmoidal accessory nasal sac, (e) axon bundles found only in the basal layer of the sensory epithelium, (f) FCs only at the top of the nonsensory epithelium, and (g) glycogen-containing MCs. Such structures seem to be unique in that they have not been observed in most teleost fishes spending their whole life in water.  相似文献   

6.
The anterior and posterior head sensory organs of Dactylopodola baltica (Macrodasyida, Gastrotricha) were investigated by transmission electron microscopy (TEM). In addition, whole individuals were labeled with phalloidin to mark F-actin and with anti-alpha-tubulin antibodies to mark microtubuli and studied with confocal laser scanning microscopy. Immunocytochemistry reveals that the large number of ciliary processes in the anterior head sensory organ contain F-actin; no signal could be detected for alpha-tubulin. Labeling with anti-alpha-tubulin antibodies revealed that the anterior and posterior head sensory organs are innervated by a common stem of nerves from the lateral nerve cords just anterior of the dorsal brain commissure. TEM studies showed that the anterior head sensory organ is composed of one sheath cell and one sensory cell with a single branching cilium that possesses a basal inflated part and regularly arranged ciliary processes. Each ciliary process contains one central microtubule. The posterior head sensory organ consists of at least one pigmented sheath cell and several probably monociliary sensory cells. Each cilium branches into irregularly arranged ciliary processes. These characters are assumed to belong to the ground pattern of the Gastrotricha.  相似文献   

7.
The rostral epithelium of a newly metamorphosed juvenile of Branchiostoma floridae was examined at the EM level to confirm previous reports on its sensory cells. The majority of the sensory cells are of three types: two type I variants, with simple collars of unbranched microvilli surrounding their cilia, and one kind of type II cell, with an extended collar of repeatedly branched microvilli. The two type I variants differ in the structure and arrangement of the microvilli, basal body and rootlet, and the length of the cilium. Both variants are probably primary sensory cells (i.e. each has its own axon), but the data supporting this conclusion are much better for one variant than for the other. Type II cells are secondary sensory cells, with synaptic terminals borne on short extensions of the cell body. The presence of degenerating type II cells suggests that they may be subject to a regular process of loss and renewal. The results do not resolve the evolutionary issue of how amphioxus sensory cells relate to the epithelial sensory and receptor cells of vertebrates. Being primary, the type I cells resemble the supposed ancestral type more closely than do type II cells. Type II cells may be chemosensory, however, and should not be ruled out a priori as possible homologues of either primary or secondary chemosensory cells in vertebrates.  相似文献   

8.
A standard procedure that combines chaetotaxic, ultrastructural and neuromorphological observations has recently provided a new perspective to the study of cercarial sensory systems. In the present work, we aimed to extend the use of this combination of techniques to investigate the chaetotaxy of Allassogonoporus sp. in conjunction with the ultrastructure of sensory receptors and neuromorphology. Five nerve regions were distinguished. A conspicuous bilobed cerebral ganglion was observed at the level of the pharynx. The chaetotaxic pattern was generally consistent with that of other lecithodendriids. Four types of receptors were distinguished with scanning electron microscopy. These types differed in cilium length (short, moderately long or long) and tegumentary collar length (moderately low or high). Internal ultrastructure of receptor type IIAL revealed an unsheathed cilium, a closed basal body, septate extracellular junctional complexes and thickened nerve collars. Some receptor types were site-specific. Long uniciliated receptors were found mainly on the dorsal surface, whereas short uniciliated receptors were widespread across the tegument. Ultrastructure and site-specificity observations suggest that most sensory receptors are mechanoreceptors, probably reflecting the important role mechanoreception plays in host finding.  相似文献   

9.
The fine structure of three sensory receptors of the rosette organ of Gyrocotyle rugosa, is described. The Type I sensory receptors, localised towards the edge of both upper and lower surfaces, are characterized by a long cilium embedded in a bulb containing two electron-dense collars and several mitochondria. The Type II sensory receptors, larger than Type I, are located on the upper surface of the rosette and have a long cilium and a ciliary rootlet. They also have two electron-dense collars and one or two mitochondria. The sensory cilia of both types are characterized by 9 + 2 axonemes. The Type III sensory receptors, localised on the under surface, lack a sensory cilium but have a ciliary rootlet and are enclosed in the tegument and musculature; there is a complicated three-dimensional spherical lattice of microfibrils associated with the rootlet. The sensory bulbs contain large numbers of membrane bound vesicles and neurotubules. A function is postulated for each of the three types of sensory receptors.  相似文献   

10.
The entire nervous system of the smallest annelid hitherto known, the dwarf male of the highly dimorphic species Dinophilus gyrociliatus , has been reconstructed by means of TEM investigations of serial ultrathin sections. Altogether there are 68 neurons, 40 of which have a sensory function. The structure and distribution of them is described. The receptor endings of the 20 sensory cells of each side are located either in two groups — the anterior receptor group and the posterior receptor group — or are singly positioned in the integument. Structural differences of the apical portion of the dendrites enables four types of receptors to be distinguished: three types with emergent cilia and one type with non-emergent cilia. Neurons with emergent cilia can be monociliated collar cells as well as mono- or multiciliated cells without collar. Special vesicle-in-vesicle structures, are located close to the basal portion of the cilia in some of these cells. The non-emergent cilia border closely to a neighbouring epidermal cell and contain a prominent intraciliary vesicle. The function of receptors is discussed with regard to a comparison with receptors in other polychaete species, structural specializations and their distribution pattern on the animal's surface.  相似文献   

11.
The sensory epithelium of the abdominal sense organ (ASO) of the scallop Mizuchopecten yessoensis is composed of three cell types, sensory cells, mucous cells, and multiciliated cells. Sensory cells bear a single long (up to 250 microm) cilium surrounded by an inner ring of nine modified microvilli and an outer ring of ordinary microvilli paired with modified microvilli. Sensory cells make up about 90% of the total number of cells in the sensory epithelium. Mucous cells, which are much wider than sensory cells, bear only ordinary microvilli on their apical surface. Rare multiciliated cells with short (4-6 microm) cilia are scattered in the periphery of the sensory epithelium sheet. All hairs, cilium, and microvilli of each sensory cell are interconnected by a fibrous network. Nine modified microvilli of a single cell are interconnected by prominent laterally running fibrous links. Membrane-associated electron-dense material of modified microvilli is connected to the ciliary membrane-associated electron-dense material by fine string-like links. These links mechanically bridge the space between the cilium and modified microvilli, as do mechanical links, described for the stereocilia and kinocilium of vertebrate vestibular and cochlear hair cells. The proximal portion of a sensory cilium is about 100 microm long and has a typical 9 x 2+2 axoneme arrangement. The distal portion of a cilium is approximately 2 times thinner than the proximal one and is filled with homogeneous electron-dense material. Along the distal portion, diffuse material associated with the external surface of the membrane is found. The rigidity of distal portion of a cilium is much less than that of the proximal one.  相似文献   

12.
B. Neuhaus 《Zoomorphology》1997,117(1):33-40
 The ultrastructure of the paired cephalic sensory organs of adult Pycnophyes dentatus and of the first juvenile stage of P. kielensis (Kinorhyncha, Homalorhagida) was investigated by TEM. In both species, each sensory organ is composed of one receptor cell and one enveloping cell which border a common intercellular lumen. A single receptor cilium extends from the receptor cell into this lumen. The cilium expands behind the basal body and branches into numerous processes. A pair of cephalic sensory organs with these characteristics belongs to the ground pattern of, at least, the Pycnophyidae. The sensory organs of these Kinorhyncha correspond closely with the anterior cephalic organs of the Gastrotricha, but differ from the known cephalic receptors of other Nemathelminthes. Currently, it cannot be evaluated conclusively whether the last common ancestor of the Nemathelminthes possessed cephalic sensory organs and, if it did, what these organs looked like. Accepted: 3 December 1996  相似文献   

13.
The structure of the olfactory organ in larvae and adults of the basal anuran Ascaphus truei was examined using light micrography, electron micrography, and resin casts of the nasal cavity. The larval olfactory organ consists of nonsensory anterior and posterior nasal tubes connected to a large, main olfactory cavity containing olfactory epithelium; the vomeronasal organ is a ventrolateral diverticulum of this cavity. A small patch of olfactory epithelium (the “epithelial band”) also is present in the preoral buccal cavity, anterolateral to the choana. The main olfactory epithelium and epithelial band have both microvillar and ciliated receptor cells, and both microvillar and ciliated supporting cells. The epithelial band also contains secretory ciliated supporting cells. The vomeronasal epithelium contains only microvillar receptor cells. After metamorphosis, the adult olfactory organ is divided into the three typical anuran olfactory chambers: the principal, middle, and inferior cavities. The anterior part of the principal cavity contains a “larval type” epithelium that has both microvillar and ciliated receptor cells and both microvillar and ciliated supporting cells, whereas the posterior part is lined with an “adult‐type” epithelium that has only ciliated receptor cells and microvillar supporting cells. The middle cavity is nonsensory. The vomeronasal epithelium of the inferior cavity resembles that of larvae but is distinguished by a novel type of microvillar cell. The presence of two distinct types of olfactory epithelium in the principal cavity of adult A. truei is unique among previously described anuran olfactory organs. A comparative review suggests that the anterior olfactory epithelium is homologous with the “recessus olfactorius” of other anurans and with the accessory nasal cavity of pipids and functions to detect water‐borne odorants. J. Morphol. 2011. © 2011 Wiley Periodicals, Inc.  相似文献   

14.
Three types of presumed sensory endings were distinguished by scanning electron microscopy: a ciliated type, a domed type, and a pit. The ciliated and domed type were also serially sectioned for transmission electron microscopy. Six of the pit type were observed, a group of 3 on each side of the oral sucker. The ciliated type were found only among the tegumental spines, and on the anterior ventrolateral surfaces except for an anterodorsal pair. The domed type resembled the ciliated type in that it had a ciliary basal body and rootlet but it lacked a cilium. It was found only in the tegument above the suckers where it probably serves as a pressure or contact receptor. Movement in vitro occurred by alternate attachment and release of the suckers with a vermiform peristalsis and the rings of spines between the suckers were considered to aid this movement in vivo.  相似文献   

15.
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.  相似文献   

16.
The patello‐tibial joint in the walking leg of the horseshoe crab can move in the flexion‐extension and promotion‐remotion planes with the freedom of movement of a ball‐and‐socket joint. Its mechanical status is represented by at least seven populations of sensory neurons and these include three different types of proprioceptors; articular membrane receptors, muscle length receptors and muscle tension receptors. A population of each of these types of proprioceptor is associated with structures on the anterior and posterior sides of each leg. In this report we describe the representation of joint movement in both planes by two populations of each type of proprioceptor. In general, the articular membrane receptors were most sensitive to joint flexion; receptors on the anterior side of the leg were biased toward promotion, while those on the posterior were biased toward remotion. Muscle length receptor activity was increased by joint extension and was slightly augmented, in posterior and anterior length receptors, by promotion and remotion, respectively. Length receptor tonic activity was a linear function of muscle length for extension but a non‐linear function of muscle flexion. Tension receptor activity was always highly dependent upon active muscular contraction. Tension receptors associated with posterior tibial flexor showed enhanced activity when the joint was promoted; the activity of those associated with the anterior flexor was enhanced by remotion. The relationships between tension receptor activity and muscle length, and between tension receptor activity and joint position, were also explored. While no single receptor population appears capable of representing the status of this joint in both planes, the output of all of the receptor populations studied appears to provide the CNS with unambiguous information about several parameters representing the status of this complex joint.  相似文献   

17.
Phalloidin‐stained whole mounts of acoel turbellarians show brightly fluorescing club‐shaped structures distributed over the epidermis and concentrated especially at the anterior and posterior tips of the body. By correlating electron micrographic images and fluorescence images of Convoluta pulchra, these structures can be seen to be sensory receptors with a central cilium surrounded by a collar of microvilli. The other candidate for showing fluorescence in the epidermis, namely gland necks, can be ruled out since their distribution is too dense to resemble the distribution of the fluorescent structures seen here. The collared sensory receptors were inserted between epidermal cells, and each bore a central cilium surrounded by a collar of 6–18 microvilli and an additional centrally positioned 2–7 microvilli of which 2 or 3 were associated with a modified rootlet called the swallow’s nest. Confocal scanning laser microscopy resolved the core of actin filaments within the microvilli of the collar and their rootlet‐like connections to the base of the sensory cell. Such receptors could also be identified by fluorescence microscopy in several other species of acoel turbellarians.  相似文献   

18.
Abstract. We examined the nuchal organs of adults of the nereidid polychaete Platynereis dumerilii by means of scanning and transmission electron microscopy. The most prominent features of the nuchal organs are paired ciliary bands located dorsolaterally at the posterior margin of the prostomium. They are composed of primary sensory cells and multiciliated supporting cells, both covered by a thin cuticle. The supporting cells have motile cilia that penetrate the cuticle and are responsible for the movement of water. Subapically, they have a narrowed neck region; the spaces between the neck regions of these supporting cells comprise the olfactory chamber. The dendrites of the sensory cells give rise to a single modified cilium that crosses the olfactory chamber; numerous thin microvillus-like processes, presumably extending from the sensory cells, also traverse the olfactory chamber. At the periphery of the ciliated epithelium runs a large nervous process between the ciliated supporting cells. It consists of smaller bundles of sensory dendrites that unite to form the nuchal nerve, which leaves the ciliated epithelium basally and runs toward the posterior part of the brain, where the perikarya of the sensory cells are located in clusters. The ciliated epithelium of the nuchal organs is surrounded by non-ciliated, peripheral epidermal cells. Those immediately adjacent to the ciliated supporting cells have a granular cuticle; those further away have a smooth cuticle. The nuchal organs of epitokous individuals of P. dumerilii are similar to those described previously in other species of polychaetes and are a useful model for understanding the development of nuchal organs in polychaetes.  相似文献   

19.
Summary The tension receptor system of the crab merus consists of two size classes of receptor cell body distributed along one face of the flexor muscle apodeme. The receptors show the general arthropod mechanoreceptor structure of cell body, connecting cilium, and sheathed sensory processes, but there are several differences. Many processes show convolutions, and the distal portion of the sensory process is embedded in the apodeme cuticle. The terminations of the sensory processes lack the usual structural specialisations for mechanotransduction. Tension transduction appears to occur by flexion of the cuticle-embedded sensory process.Work supported by an ARGC grant to Dr. D.L. MacmillanAuthor supported by Australian Commonwealth Postgraduate Research Award  相似文献   

20.
The nereid polychaete, Platynereis dumerilii, possess two pairs of post-trochophoral eyes with one vitreous body each. The development of these eyes has first been observed in 2-day-old larvae. Whether the eye anlagen arise from stem cells or from undifferentiated ectodermal tissue was not determined. At first, the anlagen of the anterior and the posterior eyes adjoin each other. They separate in late 3-day-old larvae. The first separated eye complexes consist each of two supporting and two sensory cells. The supporting cells synthesize two different kinds of granules, the pigment granules of the pigment cup and the prospective tubules of the vitreous body. These tubules accumulate in the distal process of the supporting cell. The vitreous body is formed by compartments of the supporting cells filled with the osmiophilic vitreous body tubules. The short, bulbar photosensory processes bear microvilli that emerge into the ocular cavity. At the apex of each sensory cell process, a single cilium (or occasionally two) arises. The sensory cells contain a different kind of pigment granule within their necks at the level of the pigment cup. The rate of eye development and differentiation varies. New supporting cells are added to the rim of the eye cup. They contribute to the periphery of the vitreous body like onion skins, and sensory cells move between supporting cells. The older the individual compartments of the vitreous body are, the more densely packed is their content of vitreous body tubules. Elongation of the sensory and supporting cell processes of the older cells increases the volume of the eye. The eyespots of the trochophore are briefly described as of the two-celled rhabdomeric type with a single basal body with ciliary rootlet.  相似文献   

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