The ultrastructure of the cuticle of adult female Mermis nigrescens (Nematoda)

The ultrastructure of the cuticle of the adult female nematode Mermis nigrescens has been described. There is an epicuticle and three-layered membrane covering the cuticle. The cortex is penetrated by canals which extend from the surface of the cuticle to the matrix of the layer beneath the cortex. Beneath the cortex are two layers of giant fibres which spiral around the nematode, a thick layer containing a network of fibres and a basal layer containing a vacuolated matrix material. it is thought that the epicuticle is secreted from the canals in the cortex. The possible functions of the layers in the cuticle have been discussed and similarities with the cuticle of the Acanthocephala have been noted.     

Fine structure of the epicuticle of the desert scorpion, Hadrurus arizonensis, with reference to location of lipids.

The surface and transverse sections of the epicuticle of the desert scorpion, Hadrurus arizonensis, were examined by scanning and transmission electron microscopy, respectively. Sclerite cuticle that was untreated prior to normal EM preparative procedures was compared to cuticle subjected to lipid solvents, high temperature, and concentrated alkali. Surface morphology of untreated intersegmental cuticle was also examined. The epicuticle is composed of four sublayers: outer membrane, outer epicuticle, cuticulin, and the dense homogeneous layer. Lipid solvents did not significantly alter the morphology of any of these layers or the contents of the wax canals that penetrate the cuticulin layer even though the solvents effectively remove lipids from the epicuticle for chemical analysis. The surface of the sclerite cuticle contains amorphous particles, crystalline projections, and scattered openings to dermal gland ducts. Perforations that correspond to the opening of wax canals were faintly visible after extraction of surface waxes and clearly visible after KOH treatment. No openings to dermal gland ducts or wax canals were observed in untreated intersegmental cuticle. However, wax canals are likely obscured by surface waxes similar to those present in sclerite cuticle.     

Fine structure of the cuticle of the black widow spider with reference to surface lipids

The surface and transverse sections of the cephalothorax, abdomen, and walking leg cuticle of the black widow spider, Latrodectus hesperus, were examined by scanning and transmission electron microscopy. Cuticle that was untreated prior to normal EM preparative procedures was compared with cuticle subjected to lipid solvents and/or concentrated alkali. The surface of untreated dorsal cephalothorax cuticle contained droplets and a lipid film that obscured fine surface detail. Immersing the cuticle in chloroform: methanol removed the droplets and lipid film, exposing previously covered openings to dermal gland ducts. An epicuticle, exocuticle, and endocuticle were present in all transverse sections of cuticle as was a complex system of pore and wax canals that connected the epidermis with the cuticle surface. The epicuticle of the walking leg was composed of three sublayers: outer membrane, outer epicuticle, and the dense homogeneous layer. A cuticulin layer was not observed. Lipid solvents did not significantly alter the morphology of any of these layers or the contents of the wax/pore canals.     

Ultrastructure of the penetration of the crayfish integument by the fungal parasite, Aphanomyces astaci, Oomycetes

In the crayfish, Astacus astacus, susceptible to the crayfish plague fungus, penetration of the cuticle by the parasite occurred in the soft cuticle. The zoospore lysed the surface lipid layer, tore it away, and formed an infection peg (germ tube) that penetrated through the epicuticle. A septum was formed in the infection peg, and a hypha was formed below the inner epicuticular surface. In the endocuticle, hyphae grew preferrentially parallel to the surface, occassionally perpendicular to it. Growth direction in relation to cuticle architecture is discussed. Subsequently, some hyphae started to penetrate out through the epicuticle. This process was preceded by the swelling of the hyphal tip touching the inner side of the epicuticle. The hypha penetrating out through the epicuticle was much thicker than the infection peg. Histolytic activity, combined with mechanical penetration, seems to be evident in all stages and levels except in the outward penetration of the epicuticular lipid surface layer, where only mechanical rupture could be seen. Differences in the protoplasmic ultrastructure were found between the spore and the penetrant hyphae. Penetration of the cuticle of a resistant crayfish was essentially identical to that in susceptible ones. However, inward penetration of intact epicuticle was too scarce to allow for ultrastructural studies.     

Structure of the cuticle of the alpine weta,Hemideina maori (Saussure) (Orthoptera: Stenopelmatidae)

Sclerotized cuticle segments from the thorax, dorsal abdomen, and ventral abdomen of the alpine, weta Hemideina maori (Saussure) (Orthoptera: Stenopelmatidae) were examined by light microscopy and by scanning and transmission electron microscopy. An epicuticle, exocuticle (outer and inner), mesocuticle, endocuticle, and deposition layer are present in transverse sections. The epicuticle is further composed of a cuticulin layer and inner epicuticle, the latter being finely laminated and containing narrow wax canals that terminate below the cuticle surface. Openings to dermal gland ducts are visible on the surface as are large setae and smaller sensory pegs. Frozen fractured cuticle reveals the presence of horizontal ducts or channels that run laterally within the cuticle. The structure of weta cuticle is compared with that of the common house cricket and arthropods in general.     

A freeze-fracture study of the body wall of adult, in utero larvae and infective-stage larvae of Trichinella (Nematoda)

The surface layers of the cuticle, the hypodermal membranes and the muscle membranes of the adult, the in utero larvae and the infective-stage larvae of the nematode Trichinella spiralis have been studied by means of the freeze-fracturing technique. The surface of the cuticle of both adults and larvae fractures in ways different from membranes of internal cells. The surface coat on top of the epicuticle is probably the layer that changes antigenically. Reticulate ridges, with associated particles, on the E face of the outer hypodermal membrane of the adult are probably sites of attachment of the hypodermis to the cuticle. Longitudinally arranged ridges, with associated particles, of the outer hypodermal membrane are probably points of attachment to the cuticle in the in utero and infective larvae. Rectilinear arrays of particles are present on the P face of the inner hypodermal membrane and the P face of the muscle membrane adjacent to the hypodermis of adults and larvae and probably play a role in adhesion of the muscle membrane to the hypodermis. Particle-free areas of membrane lie external to the Z bundles of the muscle cell and are similar to the sites of attachment of Z lines in insect muscles.     

An ultrastructural study of the cuticle in the marine annelid Heterodrilus (Tubificidae, Clitellata)

The ultrastructure of the cuticle in four species of the marine Heterodrilus (H. paucifascis, H. pentcheffi, H. flexuosus, H. minisetosus) is investigated with transmission electron microscopy. The noncellular cuticle consists of several parts; closest to the epidermis is a thick zone of collagen fibers embedded in a matrix. The matrix continues outside the fiber zone, forming a layered epicuticle. The external surface of the epicuticle is covered by evenly distributed, membrane-bound bodies, termed epicuticular projections. The epicuticular projections have their longitudinal axis perpendicular to the surface of the cuticle and are attached to the surface by either the surrounding membrane itself or by short pedestals. Microvilli, extensions from the epidermal cells, penetrate and sometimes pass completely through the cuticle. There is interspecific variation in the morphology of the cuticle. The four studied species differ in the arrangement of the collagen fibers, from irregularly distributed fibril bundles to orthogonally arranged fiber layers, as well as in the number and density of layers in the epicuticle. One of the studied species, H. paucifascis, shows intraspecific variation, which is associated with sample locality. The Bahamian specimens of H. paucifascis have four layers in the epicuticle, club-shaped epicuticular projections, and collagen fibers forming a less defined orthogonal grid, while the Belizean specimens have three layers in the epicuticle, epicuticular projections with a bulging part at midlevel, and a distinct orthogonal grid. Based on these findings the variation in the morphology of the cuticle appears to be dependent on both phylogenetic constraints, and functional and environmental factors.     

Structure of the cuticle of the common house cricket with reference to the location of lipids

Cuticle segments from the thorax, abdomen, and jumping legs of the house cricket. Acheta domesticus, were examined using histological techniques for light microscopy, scanning and transmission electron microscopy, and direct examination of frozen-fractured cuticle. The surface of untreated cuticle is covered by a lipid film which obscures fine surface detail. Standard EM preparative procedures, as well as washing the cuticle with ethanol before examination, remove this film exposing previously covered openings to dermal gland ducts and wax canals. An epicuticle, exocuticle, mesocuticle, endocuticle, and a deposition layer were present in all transverse sections of cuticle. Light microscopy showed that the exocuticle and mesocuticle are heavily impregnated with lipids, whereas there is little lipid associated with the endocuticle. Frozen-fractured cuticle clearly shows the ‘plywood’ structure of the meso- and endocuticle, while the exocuticle fractures as if it were a solid sheet. The epicuticle is composed of a dense homogeneous layer, cuticulin, outer epicuticle, and the outer membrane. Superficial wax was detected only in cuticle samples prepared using vinylcyclohexane dioxide as a polar dehydrant. The results were used to construct a comprehensive model of the cuticle of A. domesticus.     

The Fine Structure of the Integument of Free-Living and Parasitic Copepods. A Review

A perusal of the literature on copepod cuticles has been made, and results of the investigation of six species made by the author are included in this review. The integument of copepods is of the arthropod type. Pore canals and other structures traversing the cuticle, common in most arthropods, are not always present in free-living and some parasitic copepods. In parasitic forms, with advanced morphological changes, the cuticle is generally very thin and the epicuticle in many species forms external microvilli-like structures. In the copepods hitherto investigated the epicuticle is probably the sole layer present in the cuticle. Some copepods show specialized regions of the cuticular surface, the function of which still remains obscure. Integumental organs and integumental structures are numerous and variable. The association of bacteria with the cuticle has been observed in many species. The structure of the integument of parasitic species lacking an alimentary tube and in close contact with the host tissue or hemocoelic cavity supports the idea that the integument could be the obligatory site of nutrient uptake. In spite of the relatively few species of copepods that have been investigated, a remarkable variation of cuticular fine structure has been revealed.     

Design of the labial cuticle in Cenocorixa bifida Hung. (Hemiptera: Corixidae) with reference to ionic transport

The surface topography and ultrastructure of the labial cuticle of Cenocorixa bifida were examined by scanning and transmission electron microscopy. The dorsal wall of the labium consists of seven sclerotized transverse bars each displaying two rows of semicircular grooves and pores. The cuticle is about 20 microm thick and is composed of epicuticle and lamellate exocuticle and endocuticle, the latter separated from the underlying epidermis by subcuticle containing amorphous material. The epicuticle is subdivided into an electron-dense very thin outer epicuticle and a homogenous thick inner epicuticle, which is penetrated by grooves. The exocuticle is filled with electron-dense blocks of material, which may provide mechanical support to the labial wall. The elongate epidermal cells display extensive infoldings of the apical plasma membrane (facing the cuticle) and contain abundant mitochondria in the cytoplasm. The presence of deep epicuticular grooves and pores in the thin labial cuticle and extensive apical membrane infolding and abundant mitochondria in the epidermal cells suggest that the labium in C. bifida is the site of osmoregulatory ionic uptake.     

Trichinella spiralis: activation of complement by infective larvae, adults, and newborn larvae.

The ability of Trichinella spiralis to activate complement (C) has been addressed by several investigators. However, these investigators employed methods in which either detection of C fragments on the parasite surface or the adherence of leukocytes to the parasite was considered an indication of C activation. The present studies were undertaken to examine: (a) whether activation of C occurs via the classical and/or alternative pathway, (b) at which stage(s) of the parasite C activating capacity is acquired, and (c) what molecular entities of the epicuticle and/or cuticle are responsible for initiating C activation. Our studies indicate that T. spiralis activates C primarily via the alternative pathway (and weakly via the classical pathway) since incubation of parasites obtained from infected mice with either normal human serum (NHS) or Mg.EGTA-NHS, followed by incubation (1 hr, 37 degrees C) with antibody-sensitized sheep erythrocytes or rabbit erythrocytes, respectively, showed a time-and parasite number-dependent depletion of C. Although the three stages of T. spiralis, i.e., infective larvae, adults and newborn larvae, are capable of activating C, the newborn appears to be the most potent activator, especially when parasite number and size are taken into consideration. Further evidence of C activation is obtained from SDS-PAGE and Western blot analysis in which homogenates of parasites preincubated with NHS showed the presence of C3, C9, and C1q, whereas controls without serum were negative. Since isolated C1q was also capable of directly binding to the surface of adults and infective larvae, it is postulated that their cuticle and/or epicuticle may possess surface structures which serve as binding sites for C1q.(ABSTRACT TRUNCATED AT 250 WORDS)     

Modified pore canals in the cuticle of Gammarus (Crustacea : Amphipoda); A study by scanning and transmission electron microscopy

A novel type of pore canal is described from the cuticle of three species of Gammarus. Each canal passes from the epidermis vertically through the endocuticle and exocuticle, and in the most distal layers of the latter is slightly expanded. Before entering the epicuticle the canal narrows, forming a neck the base of which is encircled by an electron-dense collar. Several tubular structures arise from the collar and pass distally into the reticular innermost regions of the epicuticle. Within the neck and just below its opening at the cuticle surface, a rod-like structure is inserted; this protrudes a short distance from the pore. Each pore canal is connected to many necks; the openings of the latter are aligned in rows over the surface, the openings and rows being about 0.15 and 1.0 μm apart, respectively. Changes in the pore and canal contents are visible and their significance is discussed.     

Cuticle secretion during larval growth in Drosophila melanogaster

The moulting cycle and growth of the larval integument of Drosophila melanogaster has been studied by light and electron microscopy. Growth during the first, second and third larval instars is accompanied by 3.0-, 3.4- and 3.7-fold increases in surface area, respectively. Growth in surface area occurs continuously during the larval stages, with no detectable relationship to the moulting cycle. Measurements of the thickness of the cuticular layers show that the endocuticle grows in thickness by apposition and in surface area by stretching. The pre-apolytic epicuticle remains at fairly constant thickness during the increase in surface area, indicating that it grows by intussusception of new components. Post-apolytic epicuticle becomes thinner and increases in surface area by stretching. The epicuticle and pre-ecdysial endocuticle are traversed by filaments, but these do not penetrate the endocuticle secreted after ecdysis. We suggest that the filaments transport breakdown products from the old cuticle inward to the epidermis for reutilization. The growth and deposition of cuticle in two larval growth mutants, lethal (2) giant larvae and Chubby Tubby, involves mechanisms similar to those found in wild-type larvae, but in Chubby Tubby the endocuticle contains inclusions which are ultrastructurally similar to dense epicuticle.     

The distribution of phenoloxidases and polyphenols during cuticle formation

The distribution of phenoloxidase and polyphenols have been studied during cuticle formation at the 4th to 5th molt in Colpodes ethius. Cuticular phenoloxidases arise in the epidermis in cisternae of the rough endoplasmic reticulum, pass through the Golgi complex and are transported to the apical face in secretory vesicles. From the cuticular environment some enzyme is pinocytosed and broken down in the apical multivesicular bodies. Phenoloxidase and polyphenols are present during the formation of the cuticulin layer which also reacts as if it were at least partly composed of a phenoloxidase. The rest of the epicuticle incorporates phenoloxidase as it is deposited, particularly that over the dorsal tubercles which later melanize. Polyphenols do not appear until shortly before ecdysis. They are associated with the epicuticular filaments in both epicuticle and presumptive epocuticle. It is proposed that the epicuticular filaments may arise as liquid crystals with a protein component which becomes stabilized like the rest of the cuticle. These structures could provide a channel for the movement of both lipids and quinones to the surface. Phenoloxidases may pass through fibrous cuticle to be deposited as part of the epicuticle but are incorporated in fibrous cuticle scheduled for sclerotization. The time of stabilization is determined by the availability of polyphenols.     

Ultrastructural organization of hypodermis and formation of cuticle in pharate larva of Leptotrombidium orientale (Acariformes: Trombiculidae)

The ultrastructural organization of hypodermis and the process of cuticle deposition is described for the pharate larvae of a trombiculid mite, Leptotrombidium orientale, being under the egg-shell and prelarval covering. The thin single-layered hypodermis consists of flattened epithelial cells containing oval or stretched nuclei and smooth basal plasma membrane. The apical membrane forms short scarce microvilli participating in the cuticle deposition. First of all, upper layers of the epicuticle, such as cuticulin lamella, wax and cement layers, are formed above the microvilli with plasma membrane plaques. Cuticulin layer is seen smooth at the early steps of this process. Very soon, however, epicuticle starts to be curved and forms particular high and tightly packed ridges, whereas the surface of hypodermal cells remains flat. Then a thick layer of the protein epicuticle is deposited due to secretory activity of hypodermal cells. Nearly simultaneously the thick lamellar procuticle starts to form through the deposition of their microfibrils at the tips of microvilli of the apical plasma membrane. Procuticle, as such, remains flat, is situated beneath the epicuticular ridges and contains curved pore canals. Cup-like pores in the epicuticle provide augmentation of the protein epicuticle mass due to secretion of particular substances by cells and to their transportation through the pore canals towards these epicuticular pores. The very beginning of the larval cuticle formation apparently indicates the starting point of the larval stage in ontogenesis, even though it remains for some time enveloped by the prelarval covering or sometimes by the egg-shell. When all the processes of formation are over, hungry larvae with a fully formed cuticle are actively hatched from two splitted halves of prelarval covering.     

Immune suppression of Galleria mellonella (Insecta,Lepidoptera) humoral defenses induced by Steinernema feltiae (Nematoda,Rhabditida): involvement of the parasite cuticle

Immune depression of Galleria mellonella larvae was evaluated a short time after infection with the entomopathogenic nematode Steinernema feltiae. In the host the activity of the enzymatic cascade known as the proPO system was significantly reduced by the presence of either live or dead parasites. The presence of parasites decreased the LPS-elicited proPO system activity. In addition, this process seems to be related to a decrease in the activity of hemolymph proteases, more than to phenoloxidase damage. proPO inhibition was also achieved by injected isolated cuticle fragments, suggesting that the parasite body surface plays an important role in the early parasitation phase.     

The fine structure and deposition of the larval cuticle of the sheep blowfly (Lucilia Cuprina)

The cuticle of Lucilia is composed of an untanned endocuticle and a complex epicuticle of four layers, superficial layer, outer epicuticle, cuticulin and dense layer. The outer epicuticle and attached epicuticular filaments are resistant to acid hydrolysis. During deposition of the cuticle of each larval instar, the cuticulin and dense layers are formed first, followed by the outer epicuticle, which appears to be laid down by secretions from the epidermis passing through the cuticulin via epicuticular filaments. The outer epicuticle is found in the position normally occupied by the wax layer of other insect species.     

Some ultrastructural observations on the integument of a pentastomid

The cuticle of the cephalobaenid pentastomid Reighardia sternae is described at various stages of the moult-intermoult cycle. The intermoult cuticle comprises four layers: an outer epicuticle; an underlying dense layer, the protein epicuticle; a fibrillar endocuticle; and a denser subcuticle. The overall similarity between the structure and composition of these layers and those of insects is discussed. However, the orientation of the chitin-protein fibres in the endocuticle does not show the rotating structure characteristic of many arthropod species, but this does appear in the sclerotized hooks. It is suggested that this comparatively loose, poorly oriented endocuticular structure produces a highly extensible cuticle which is precisely adapted to the specialized, endoparasitic habit of this species. Events at ecdysis, particularly the secretion of moulting fluid and the deposition of cuticulin, follow the insect pattern precisely. The phyletic significance of these observations is discussed.     

Nonspecific Factors Involved in Attachment of Entomopathogenic Deuteromycetes to Host Insect Cuticle

The attachment of the conidia of the insect-pathogenic fungi Nomuraea rileyi, Beauveria bassiana, and Metarrhizium anisopliae to insect cuticle was mediated by strong binding forces. The attachment was passive and nonspecific in that the conidia adhered readily to both host and nonhost cuticle preparations. The hydrophobicity of the conidial wall and the insect epicuticle appeared to mediate the adhesion process. Detergents, solvents, and high-molecular-weight proteins known to neutralize hydrophobicity reduced conidial binding when added to conidium-cuticle preparations. However, these chemicals did not remove the hydrophobic components from the epicuticle or from conidial preparations. The outer surface of the conidium consists of a resilient layer of well-organized fascicles of rodlets. Intact rodlets extracted from B. bassiana conidia bound to insect cuticle and exhibited the hydrophobicity expressed by intact conidia. Both electrostatic charges and various hemagglutinin activities were also present on the conidial surface. However, competitive-inhibition studies indicated that these forces played little, if any, role in the adhesion process.     

Cuticular adaptations in two parasitic copepods in relation to their modes of life

The structure, histochemistry, and possible functional properties of the cuticle in two parasitic copepods Pennella elegans Gnanamuthu and Caligus savala Gnanamuthu have been studied: the former is partially embedded in the host while the latter is an ectoparasite capable of free swimming.In Pennella elegans the cuticle of the embedded anterior region of the body is soft, colourless, and lacks an outer epicuticle while that of the posterior exposed part is pigmented and hard. Conspicuous in the cuticle of the ventral region of the head are pore canals which, though not chitinized, are functional even in the intermoult stage: these canals may be involved in the transport of nutrient materials from the host. The horns, which serve to fix the parasite firmly in the host tissues, are covered by cuticle in which the epicuticle and outer layers of the procuticle are hardened by formation of disulphide linkages. The cuticle of the neck region is not hardened and the procuticle in this region shows transverse regions of dense and light zones probably related to the coiling of the neck during penetration. The epicuticle is two layered in the cuticle of the exposed posterior region, the inner epicuticle and outer region of the procuticle being partially hardened by phenolic tanning so confer rigidity and resistance. The cuticle of the plumes is soft and devoid of an outer lipid epicuticle and so possibly adapted for a respiratory function.In Caligus savala, the epicuticle is two layered, and the procuticle has pigmented, calcified, and uncalcified layers. The cuticle is hardened by phenolic tanning as well as by calcification thus recalling the cuticular organization of decapod crustaceans.