Ultrastructure of a possible new type of crustacean cuticular strain receptor in Carcinus maenas (crustacea,decapoda)

A hitherto unknown sensillum type, the “intracuticular sensillum” was identified on the dactyls of the walking legs of the shore crab, Carcinus maenas. Each sensillum is innervated by two sensory cells with dendrites of “scolopidial” (type I) organization. The ciliary segment of the dendrite is 5–6 μm long and contains A-tubules with an electron-dense core and dynein arm-like protuberances; the terminal segment is characterized by densely packed microtubules. The outer dendritic segments pass through the endo- and exocuticle enclosed in a dendritic sheath and a cuticulax tube (canal), which is suspended inside a slit-shaped cavity by cuticular lamellae. The dendrites and the cavity terminate in a cupola-shaped invagination of the epicuticle. External cuticular structures are lacking. Three inner and four to six outer enveloping cells are associated with each intracuticular sensillum. The innermost enveloping cell contains a large scolopale that is connected to the ciliary rootlets inside the inner dendritic segments by desmosomes. Scolopale rods are present in enveloping cell 2. Since type I dendrites and a scolopale are regarded as modality-specific structures of mechanoreceptors, and since no supracuticular endorgan is present, the intracuticular sensilla likely are sensitive to cuticular strains. The intracuticular sensilla should be regarded as analogous to insect campaniform sensilla and arachnid slit sense organs.     

The fine structure of haltere sensilla in the blowfly Calliphora erythrocephala (Meig.), with scanning electron microscopic observations on the haltere surface

The dipteran haltere incorporates large numbers of regularly disposed mechanoreceptors providing the sensory input enabling the vibrating haltere to function as a gyroscopic organ of equilibrium. Campaniform sensilla of the basal and scapal regions have been investigated by light and transmission electron microscopy, and these observations are augmented by scanning electron studies of the cuticle overlying the groups of sensilla. Each sensillum possesses a specialized fan-shaped terminal containing a complex and ordered association of microtubules and filaments. The transmission of stress to this region via the cuticle, and its possible role in transduction is considered. The fine structure of apical and basal sections of the distal sensory process and associated sheath cells is described; the functional significance of the distribution of mitochondria and other components is discussed. The organization of haltere chordotonal sensilla is described briefly, and compared with other mechanoreceptors with particular reference to microtubules and scolopale structures.     

Structure of the abdominal receptor responsive to internally applied pressure in the blood-feeding insect,Rhodnius prolixus

Summary The sensory receptor responsive to pressure applied internally to the ventral abdominal body wall of the blood-feeding insects, Rhodnius prolixus, is a single sense cell containing, at its distal end, a cilium enclosed within a scolopale, a densely staining structure characteristic of insect scolopidial sensilla. A small spherical structure lies within a dilation near the midregion of the cilium, and contains nine heavily staining bodies, the position of each corresponding to a pair of microtubules in the cilium. Proximal to the dilation, the microtubules are organized in a ring of nine pairs with one microtubule of each pair associated with dyneinlike arms. Dastal to the dilation a central pair of microtubules is present, but dyneinlike arms are absent. The scolopale cell, which gives risc to the scolopale, has cytoplasmic invaginations that form an elaborate array of extracellular compartments surrounding the body wall of the sense cell. These compartments may serve to dampen high frequency vibrations permitting the receptor to respond to pressure exerted by touch, an attribute in keeping with the receptor's proposed function of detecting abdominal distension related to the size and movement of the stomach.     

The fine structure of a cephalic sensory receptor in the copepod Doropygus seclusus Illg (Crustacea: Copepoda: Notodelphyidae)

A cephalic organ of presumed sensory function is described in nauplii and copepodids of the ascidicolous copepod Doropygus seclusus Illg. The receptor, located bilaterally in the anterodorsal head region, is composed of dendrites of extra optic protocerebral origin which have ciliary protrusions with basal bodies, no rootlets, and a basal infrastructure of the 9 + 0 type. The cilia do not branch and their distal terminations contain only one to four microtubules. In nauplii and free-living copepodids, a large epidermal supporting cell encapsulates the end of one dendrite and its cilia in a sac. Other dendrites and their cilia pass through the supporting cell and, terminally, the cilia escape to form a whorled fascicle which contacts the anterolateral cephalic cuticle. The latter end organ reaches its greatest development in the second copepodid stage — the stage which infects the ascidian. All of the symbiotic stages of the copepod have only a proportionately smaller end organ of the saccular type and apparently lack the end organ consisting of whorls of ciliary ends. The function of the receptor is unknown, but it is suggested that the end organ which disappears in the symbiotic stages functions in second copepodids in host recognition.     

Are the funnel-canal organs the ‘campaniform sensilla’ of the shore crab,Carcinus maenas (Decapoda,Crustacea)?

Summary The funnel-canal organs on the dactyls of the shore crab, Carcinus maenas, are innervated by 3–24 sensory cells with unbranched dendrites, which attain a length of 500–1400 m. The outer dendritic segments are enclosed in a dendritic sheath and pass through the cuticle within a canal. Two dendrite types can be distinguished according to ultrastructural criteria: Type I has a long ciliary segment, A-tubules with an osmiophilic core and arms, and a thick ciliary rootlet. Type II possesses only a short ciliary segment and a thin ciliary rootlet. Each funnel-canal organ contains two type-I dendrites. Their ciliary bases appear a few m distal to those of the type-II dendrites (1 to 22 in number). Two inner and two to eight outer enveloping cells belong to a sensillum. The innermost enveloping cell contains a large scolopale. In the second enveloping cell single scolopale rods are present. Thus, the funnel-canal organs are characterized by structural features typical for mechano-sensitive scolopidia, on the one hand, and for chemoreceptors, on the other. Therefore, the funnel-canal organs are very likely bimodal sensilla (contact chemoreceptors). A comparison with other arthropod sensilla shows that cuticular mechanoreceptors of aquatic crustaceans generally exhibit a scolopidial organization.     

Cytology of various antennal setae in a troglobitic Mysidacea (Crustacea)

Summary The various antennal setae can be differentiated from each other by the number and the type of their dendrites and by the cuticular structure of their external parts; these features correspond to functional differences. Moreover, the work revealed differences in relation to the corresponding setae of a marine Mysidacea previously studied by Guse (1978). Various hypotheses linking the ultrastructural differences to those that characterize the environments in which these two species live can be put forward.Abbreviations A1, A3 simple setae A1, A3 - An antenna - B1, B2 setulate setae B1, B2 - Bi bifid seta - bp bending plane - c1, c2, c3 type 1, 2, or 3 cilia (outer dendritic segments) - cu cuticle - d1, d2, d3 type 1, 2, or 3 dendrites (inner dendritic segments) - ec enveloping cell - g Golgi apparatus - h helically arranged cuticle - md microtubule doublet - n nucleus - p apical pore - r ciliary root - s setules - sc scolopale - scc scolopale cell - Si sickle-shaped seta - sm small seta - st stopper - t extracellular matter tube     

Structure of the auditory system of the weta Hemideina crassidens (Blanchard, 1851) (Orthoptera,Ensifera, Gryllacridoidea,Stenopelmatidae)

Summary This study of the ultrastructure of the auditory sensilla of the New Zealand weta, Hemideina crassidens, is the first such study on a member of the orthopteran Superfamily Gryllacridoidea. Ultrastructure of the auditory sensilla is similar in all of the tibial mechanosensory organs, here called subgenual organ, intermediate organ and crista acoustica by analogy with comparable structures in Tettigoniidae.Distal to each sensory soma is a dendrite containing multiple ciliary rootlets that fuse into a single ciliary root. This splits into nine root processes that pass around the outside of the proximal basal body and then rejoin at the level of the distal basal body, distal to which the dendrite has a modified ciliary structure with a circlet of nine peripheral paired tubes and rods as it passes through the proximal extracellular space. It is then enclosed by a zone of scolopale cell cytoplasm before expanding into a dilatation within the distal extracellular space. In some sensilla this space is partially occluded by electron dense material which is part of the scolopale cell. Distal to the dilatation the cilium shrinks and ends surrounded by the scolopale cap.Accessory cells consist of glia enwrapping the sensory neuron in the region of its soma, the scolopale cell surrounding the ciliary portion of the dendrite, and the attachment cell surrounding the scolopale cell and scolopale cap and connected to them by desmosomes. The attachment cells are filled with microtubules in differing densities and orientations. Lamellae are present in the acellular matrix surrounding the attachment cells. Banded fibres, presumably of collagen, are also present in the matrix.     

A new mechanosensory organ on the anterior spinnerets of the spiderCupiennius salei (Araneae,Ctenidae)

We describe hitherto unknown mechanoreceptors on the anterior spinnerets of the spiderCupiennius salei. These receptors are found at the base of the spigots of the major ampullate glands which produce the dragline used by the spider as a safety thread in various behavioral situations. There are 40–60 mechanoreceptors associated with two spigots of each anterior spinneret. They are likely to provide information on the forces pulling on the dragline and also on its orientation in space. A single sensillum consists of a hole in the cuticle covered by a thin cuticular membrane. It much resembles spider slit sensilla, which are known to detect strains in the exoskeleton. Each sensillum is supplied by two dendrites most likely belonging to two bipolar sensory cells. One of the dendrites ends at the covering membrane and the other more proximally. The sensilla are arranged with their long axes roughly parallel to the circumference of the spigots. External forces, transmitted by the dragline, result in deformation of the central part of the cuticular plate at the base of the spigots and thus in stimulation of the sensilla. This is shown electrophysiologicallly. Considering their morphology, topography, and electrophysiology, these mechanoreceptors are suggested to be important in the sensory control of dragline release by the spider.     

Structure of the green lacewing tympanal organ (Chrysopa carnea,neuroptera)

Small swellings near the base of the radial vein in each fore wing of the green lacewing, Chrysopa carnea, resemble typical insect tympanal organs, but some important differences are apparent. The swellings are bounded dorsally and laterally by thick cuticle and ventrally by thin, membranous cuticle. The ventral membrane is formed by a single, thin sheet of exocuticle with flattened hypodermis internally, but lacks the tracheal component that forms part of the tympanum in the typical insect tympanal organ. The portion of the membrane beneath each swelling is rippled while proximally it is smooth. In contrast to typical insect tympanal organs, the swellings in C. carnea are largely fluid-filled since an unexpanded trachea runs through each organ. A distal and a proximal chordotonal organ composed of typical chordotonal sensory units are associated with each swelling. The distal organ contains from five to seven units while the proximal organ is composed of from 18 to 20 units. Each sensory unit is composed of three readily identifiable cells. Distally, an attachment cell unites with the membrane and is contiguous with the scolopale cell, which surrounds the dendrite of the bipolar neuron. On the basis of the morphological evidence, one would not expect these swellings to function as sound receptors. However, the results of physiological and behavioral experiments, presented elsewhere, show that these organs are receptors for ultrasound.     

Femoral chordotonal organ in the legs of an insect,Chrysoperla carnea(Neuroptera)

The femoral chordotonal organ (FCO) inChrysoperla carneais situated in the distal part of the femur and consists of two scoloparia, which are fused at their distal end. The distal scoloparium contains 17-20 scolopidia, and the proximal one six scolopidia. Each scolopidium consists of two sensory cells and three types of enveloping cells (glial, scolopale and attachment cell). The sensory cells of different scolopidia do not lie at the same level in the FCO. Therefore the attachment cells of different scolopidia have different lengths. In the FCO, three types of ciliary roots are found in different sensory cells. The dendrite of the sensory cell terminates in a distal process, which has the structure of a modified cilium (9x2+0). The very distal part of the cilium is surrounded by an extracellular electron dense material, the cap, and ends in a terminal dilation. The scolopale cell contains the electron dense scolopale rods, consisting of plentiful microtubules. In their middle third the scolopale rods are fused and form the scolopale. In the FCO septate junctions, desmosomes and hemidesmosomes are found.     

Light- and electron-microscopic analysis of the statocyst of the American crayfishOrconectes limosus (Crustacea,Decapoda)

Summary The statocyst ofOrconectes limosus contains static hairs arranged in four groups. All the hairs are the same in basic structure; they differ only in length and diameter and in their positions with respect to the other hairs in the group and to the statolith. In terms of functional morphology, each static hair is part of a unit consisting of an acellular lever string, three receptor cells, a scolopale cell, sheath cells, and enveloping cells. The lever string comprises two components in a characteristic longitudinal arrangement. The structure of the receptor cells resembles that of the arthropod chemo- and mechanoreceptors studied previously. The cilium and the postciliary section lie within two receptor cavities, formed by the scolopale cell and the sheath cells; the two cavities communicate with one another. The receptor cells are fixed in position by various structures. Proximally they form desmosomes with the scolopale cell, medially they are joined by filaments to the inner wall of cavity 1, and distally they are retained by a constriction between the two cavities. Two possible stimulus-mediating mechanisms are discussed: pressure changes in the receptor cavities and shearing of the base of the cilia with respect to the preciliary region. The lever string is part of the cuticle and hence is shed during molting. Nevertheless, the statocyst remains functional during this process because new structural units are formed below the old cuticle prior to ecdysis.Abbreviations a axon - b bulb - bb basal body - c cilium - cu cuticle - d dendrite - de desmosome - dm dense material - ec enveloping cell - f fulcrum - h hair - hs hair shaft - ir inner row of hair group - l lingula - ls lever string - m mitochondrion - n nucleus - or outer row of hair group - pcd postciliary dilation - R1 receptor cavity 1 - R2 receptor cavity 2 - rc receptor cell - ro rootlet - s sheath cell - sc scolopale cell - st statoconium - t tooth     

Alterations of ultrastructure and physiology of chemoreceptor dendrites in blowfly taste hairs treated with vinblastine and colchicine

Vinblastine (10^?3 M) and colchicine (10^?2 M) dissolved in fly Ringer solution were applied to chemoreceptor dendrites in individual tarsal taste hairs of blowflies (Phaenicia serricata Meigen), and the resultant changes in the morphology and physiological responsiveness of the receptors were examined. While Ringer solution alone did not have any morphological or physiological effects, treatment with drugs dissolved in Ringer solution increased the latency of responses to sucrose and NaCl and decreased spike amplitude and frequency. The drugs also disrupted microtubules and caused the destruction of the distal end of the dendrites. The observations provide evidence that the microtubules have a role in maintaining the structural integrity of the dendrites. Anodal current applied along with a chemical stimulus (NaCl or sucrose) increased the action potential frequency of treated and untreated receptors, and the electrical current elicited spikes only from those receptors which were activated by the chemical stimulus alone. When drug treatment resulted in a complete cessation of response to chemical stimuli, the receptors were also unresponsive to electrical stimulation. The results of this study are discussed in relation to hypotheses of transduction in chemoreception.     

The formation of the epicuticle and associated structures inOniscus asellus (Crustacea,Isopoda)

Summary The integument of the woodlouse,Oniscus asellus, consists of a two-layered epicuticle, a largely lamellate procuticle — itself divided into two regions (pre-and postecdysial cuticles), and the epidermis. At the initiation of new cuticle production the epidermal cells become vacuolated and retract away from the cuticle. Apolysis occurs immediately after the cessation of postecdysial cuticle production. The formation of the epicuticle is unique among the arthropods since material aggregates along the distal epidermal membrane. By indenting, doubling back on itself, and incorporating septa, the epicuticle forms surface structures such as plaques and tricorns.The innervation, and so the receptive function of the tricorns is confirmed, but since there is no connection between the old and new receptors during premoult, sensory information from these exoreceptors must be severely curtailed. This may explain the biphasic moult in all isopods since it ensures that only half the body experiences this sensory deprivation at any one time. In terrestrial species there is the additional advantage of restricting the area of permeable new cuticle. The frequency of moulting may be due to the need to renew disrupted receptor surfaces.Tricorns do not appear to be the mechanoreceptors involved in the marked thigmotactic response of woodlice since they do not have the typical internal structure of such receptors; rather, the dendrite —which extends into the lumen of the tricorn —is protected from deformation by the previously unreported combination of a dendritic sheath and a cuticular tube. The modality of tricorns is possibly one of hygro-perception. One of the behavioural responses of woodlice to desiccation is aggregation. The numerical distribution of tricorns over the body surface is admirably suited to assist in the formation and maintenance of such aggregates during desiccation and to their observed dispersal when the relative humidity rises.     

The metathoracic wing-hinge chordotonal organ of an atympanate moth,Actias luna (Lepidoptera,Saturniidae): a light- and electron-microscopic study

Summary The structure of a simple chordotonal organ, the presumed homologue of the noctuoid moth tympanal organ, is described in the atympanate moth, Actias luna. The organ consists of a proximal scolopidial region and a distal strand, which attaches peripherally to the membranous cuticle ventral to the hindwing alula. The strand is composed of elongate, microtubule-rich cells encased in an extracellular connective tissue sheath. The scolopidial region houses three mononematic, monodynal scolopidia, each comprised of a sensory cell, scolopale cell, and attachment cell. The dendritic apex is octagonally shaped in transverse section, its inner membrane lined by a laminated structure reminiscent of the noctuoid tympanal organ collar. A 9+0-type cilium emerges from the dendritic apex, passes through both the scolopale lumen and cap, and terminates in an extracellular space distal to the latter. Proximal extensions of the attachment cell and distal prolongations of the scolopale cell surrounding the cap are joined by an elaborate desmosome, with which is associated an extensive electron-dense fibrillar plaque. Within the scolopale cell, this plaque constitutes the scolopale rod material. The data are discussed in terms of both the organ's potential function, and its significance as the evolutionary proto-type of the noctuoid moth ear.     

The fine structure of distal receptors on the labium of the aphid,Brevicoryne brassicae L. (Homoptera)

Summary Short peg receptors located at the distal tip of the aphid labium have the structure of mechanoreceptors. Each peg is innervated by a single sensory nerve which is anchored eccentrically to a basal cuticular tube and terminates in electron-dense material in the base of the peg. The arrangement and eccentric insertion of the eight pegs in the labial wall on one side of the stylet groove, with the eccentric insertions of their innervating neurones, provide a mirror image of the receptors on the opposite side. On the basis of a comparison of the structure of these receptors with that of tactile receptors for which electrophysiological data on sensitivity are available, it is possible to predict that the receptors detect both surface contact (pressure) and surface profile; and that the bilateral symmetry in the receptor arrangement facilitates the detection of vein contours which are preferred settling sites on the leaf. The structure of the dendritic terminal and its insertion is that of a well reinforced cytoskeleton designed to transmit tension to the cell membrane, in agreement with the concept that transduction is a membrane related phenomenon. The distal microtubules, fifty per-cent of which originate as well as terminate in the tubular body, are packed in electron-dense material which binds to the cell membrane. The membrane in turn is attached to cuticular components of the receptor. Abrupt changes in dimension of the dendritic outer segment may be designed to modulate the conduction of a membrane potential. On the other hand, lack of continuity in the microtubules makes these organelles poor candidates for the transduction of excitation from a distal site of stimulation to a proximal region.Supported by operating grants Nos. A 6063 and A 9856 from NRCC     

东亚飞蝗Locusta migratoria manilensis（Mey．）膝下器中具橛感器的附属细胞和附属结构的超微结构

东亚飞蝗膝下器的具橛感器主要由三类细胞组成．即：感觉细胞、感橛细胞和冠细胞。感觉细胞为具橛感器的主要结构和功能细胞,其超微结构已在其他的文章中描述。感橛细胞是具橛感器的主要支持细胞,从近端到远端依次与神经胶质细胞、感觉细胞的远端树突部分和感觉纤毛部以及顶端细胞外结构——冠、冠细胞直接接触．感橛细胞内最明显的结构为感概,另外,感橛细胞质被高度“空化”。冠细胞紧密包围着感橛细胞和冠,冠细胞中含有大量的纵行微管．并将整个具橛感器连接到体壁上。     

The cercal sensilla of the blowfly Lucilia cuprina. I. Structure of the sockets and distal dendritic regions

The functions of the gustatory, olfactory, touch and stress receptors on the cerci of Lucilia cuprina Wied. (Diptera: Calliphoridae) are apparent from the morphology of their distal dendritic segments and associated cuticular structures. Each trichoid mechanoreceptor has a dendrite containing a tubular body at the base of the hairshaft. The suspension fibres and socket septum may be involved in transmitting a stimulus to the dendrite terminal and restoring the hair to its resting position. The campaniform sensilla are considered as trichoid mechanoreceptors with reduced hair shafts and socket structures, reflected in fusion of the suspension fibres into the inner cuticle of the dome and loss of the socket septum. Fusion and reduction of the socket structures is also apparent at the bases of the olfactory pegs. They differ from typical antennal olfactory sensilla in having a flexible socket and relatively thick walls; features which may protect them from damage during ovipositor probing of potential oviposition substrates. The two types of cereal gustatory sensilla differ in their complement of chemosensory dendrites, one has three, the other four, the latter type also has a mechanoreceptive dendrite at the base of the hair shaft. Both types have socket structures resembling those of the trichoid mechanoreceptors.     

Functional morphology of the subgenual organ of the carpenter ant

Using light microscopy, confocal microscopy, electron microscopy and histochemistry, the subgenual organ (SGO) of an ant, Camponutas ligniperda, is investigated. Sensory units and attachment cells together enclose a large extracellular cavity, which is filled by acid mucopolysaccharides, as revealed by staining with ruthenium red. Due to this cavity, the whole SGO has the shape of a deformed sphere and the scolopidia exhibit a distribution of angles between 0 degrees and 60 degrees with the tibial long axis (as is shown by phalloidin-rhodamin staining of the actin filaments of the scolopale, viewed in situ by laser scanning confocal microscopy). The subgenual organ is innervated by a branch of the tibial nerve, which splits within or shortly distal to the femur-tibia joint. The other features of the SGO of Camponotus ligniperda are similar as in other insects: the SGO of Camponotus ligniperda contains about 35 scolopidial sensilla; it is fixed to the subgenual nerve on its proximal end, by its attachment cells to the opposite part of the cuticle; the fixation by the attachment cells is accomplished by a vast quantity of cytoplasmic microtubules; the construction of the sensory units is the same as in other mononematic scolopidial organs. The role of the extracellular lumen inside the organ and the special shape of the SGO of Camponotus ligniperda in mechanical transmission is discussed.     

Bimodal innervation of the infrared organ of Merimna atrata (Coleoptera,Buprestidae) by thermo- and mechanosensory units

The pyrophilous Australian “fire-beetle” Merimna atrata approaches forest fires and possesses abdominal infrared (IR) organs. Each round IR organ is centrally innervated by a sensory complex showing two different units: one thermoreceptive multipolar neuron and one mechanosensitive chordotonal organ (CO) consisting of two scolopidia. We investigated the CO and found that the scolopidia are mononematic (the scolopale cap remains below the cuticle) and monodynal (one sensory cell per scolopidium). The dendrites of the scolopidia extend anteriorly and are attached by their caps to the cuticle about in the middle of the absorbing area. Structural features at the site of innervation suggest that the CO measures minute thermal deformations caused by IR absorption. Therefore, an additional photomechanic component which has been described for the IR receptors of pyrophilous jewel beetles of the genus Melanophila can be proposed for the IR organ of Merimna. Because scolopidia can measure displacements in the subnanometer range, the CO may enhance the sensitivity of the IR organ. The sensory complex of the Merimna IR organ shows the same units and similar cuticular modifications as the tympanal organs of some noctuid moths. Therefore, a parallel evolution of insect ears and the Merimna IR organ is discussed.     

The fine structure and possible function of the sensory setae of the penis of Balanus balanoides (L.)

The structure and innervation of the sensory setae which are present in large numbers on the penis of Balanus balanoides (L.) have been established by scanning and transmission electron microscopy. Each seta contains a small number of sensory dendrites surrounded by an extracellular supporting tube which is presumed to be secreted by the enclosing sheath cell. The dendrites, which distally extend beyond both the sheath cell and supporting tube, terminate at the tip of the seta within a pore-like invagination of the cuticle and thus are in direct contact with the environment. Proximally bundles of dendrites pass into the penis tissue where they are surrounded by several sheath cells. The supporting tube terminates at a point within the body of the penis where a series of intracellular rods arise. The ciliary character of the dendrites is evident in this region, the microtubules being organized into the (9 × 2) +2 pattern. It is deduced that the sensilla are chemosensory; their structure is compared with that of other crustacean sensilla which are presumed to be chemosensory.