Fine structure and morphogenesis of the sclerite epicuticle in the Atlantic shore crab Carcinus maenas

Three basic sublayers are identified in the epicuticle of the mineralised sclerites of the Atlantic shore crab Carcinus maenas (Crustacea, Decapoda): the surface coat, the cuticulin layer, and the inner epicuticle. Their morphogenesis and subsequent changes are described throughout the moulting cycle in the normal cuticle and the cuticular structures, namely the sensory bristles and epicuticular spines. At first, the cuticulin layer begins to form just after apolysis. This layer is built directly over the plasma membrane and immediately appears as a membrane-like structure 40 nm thick, composed of five symmetrically arranged laminae: two inner electron-lucent leaflets sandwiched between two thick electron-dense leaflets and separated by a thin dense median stratum. Elaboration of the inner epicuticle below the cuticulin layer is thought to occur via an intussusceptive process involving the pore canal cell extensions as transport routes. The inner epicuticle is made of vertically oriented microfibres embedded in an electron-dense matrix material. During the second half of the premoult period, the surface coat is deposited on the upper side of the cuticulin layer.     

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.     

The structure of an epidermal cell during the development of the protein epicuticle and the uptake of molting fluid in an insect

A structure for a generalized insect epidermal cell during the formation of the epicuticle is proposed, based on studies of several different epidermal cell types. The protein epicuticle is defined as the dense homogeneous layer below the cuticulin. The formation of the protein epicuticle involves secretory vesicles arising in Golgi complexes, and marks an interlude in the involvement in cuticle formation of plasma membrane plaques. The plaques are concerned in cuticulin formation before and in fibrous cuticle formation after the deposition of the protein epicuticle. The epidermis is characterized by the possession of a cytoskeleton of microtubules and a matrix of microfibers. In the elongated cells forming bristles and spines, the microfibers are often oriented in bundles with an axial banding which repeats every 120 Å. The microtubules are also arranged in columns with a trigonal packing and center to center spacing of about 800 Å. These cytoskeletal structures separate the other organelles into channels which may restrict the pathways open for the movement of secretory and pinocytotic vesicles. The protein epicuticle arises from the secretory vesicles which discharge at the apical surface. The contents disperse and reaggregate below the cuticulin. The Golgi complexes in the basal and central regions have many secretory vesicles and a small saccular component, differing from those nearer the apex which are smaller and have fenestrated saccules. The small coated vesicles (800 Å in diameter) associated with both sorts of complex, probably move to the apical and basal faces of the cell where they may give rise to the large coated vesicles (2000 Å in diameter) inserted in the plasma membrane. Pinocytosis occurs from both apical and basal faces but most lytic activity is in the apical region. Plant peroxidase injected into the haemocoel is taken up basally and transported to the apical MVBs. The large coated vesicles on the apical face may be concerned in the control of the extracellular subcuticular environment. They appear to fill up and detach, fusing to become the apical MVBs.     

Cuticle formation in the embryo of Drosophila melanogaster

In Drosophila melanogaster embryos cuticle formation occurs between 12 and 16 hours of development at 25°C. The formation of the cuticulin and the protein epicuticular layers is simultaneous in the hypoderm, the tracheoblasts, and the fore- and hindgut cells. The cuticulin forms as a dual lamina, aggregating from granules secreted by the hypodermal cells. This is followed by the formation of a granular protein epicuticle and finally by the secretion of a mixed fibrous and granular endocuticle. All secretory cells are relatively simple in their ultrastructure. The secretory process is a membrane phenomenon, occurring at the tips of hypodermal microvillae on cells at the surface of the embryo and on those hypodermal cells lining the lumen of the fore- and hindgut. It also occurs along the entire surface of the tracheoblast lumen as well as on the outer surface of those cells which form exoskeletal chitinous setae. The process involves a specialization of the plasma membrane with the formation of secretory granules intracellularly beneath the membrane and the extrusion of these granules through the membrane to the outside where final cuticle formation occurs.     

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.     

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.     

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.     

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.     

An ultrastructural study of the mantle of the barnacle, Elminius modestus Darwin in relation to shell formation

The fine structure of the mantle and shell of the barnacle, Elminius modestus Darwin has been examined by electron microscopy. The epithelial cells along the outer face of the mantle differ in size, shape, and organelle complexity according to the different components of the shell they secrete. The shell consists of a non-calcareous basis and calcareous mural and opercular plates which are connected by a flexible opercular hinge. Both the basis and opercular hinge are composed of two main units: an outer cuticulin layer and a lamellate component of well ordered arched fibrils. During the deposition of the latter structures morphological changes in the cells occur which may be correlated with the moulting cycle. Preliminary results show that the calcareous plates are covered by an outer epicuticle, which is bordered by a cuticulin layer; the inner calcareous component, consists of an orderly arrangement of organic matrix envelopes within which crystals may be initiated.

The cells lining the inner surface of the mantle are uniform in appearance with a thin cuticle at their free surface which lines the body cavity. The latter structure of the cuticle and manner of its deposition are similar to those of the basis and opercular hinge. Separating the outer and inner mantle epithelial cells is connective tissue which comprises several differing cell types. The possibilities are discussed of the rôle these cells may play in shell deposition. The modes by which underlying cells secrete the different shell components and the cuticle lining the inner face of the mantle, are also discussed.     

The structure and formation of the cuticulin layer in the epicuticle of an insect, Calpodes ethlius (Lepidoptera, Hesperiidae)

The cuticulin layer is defined as the dense lamina (120–175 Å thick in Calpodes larvae, depending upon the stage) forming the outer part of the epicuticle in insects. It completely invests an insect except for the gut and the openings of some sense organs. It is the first layer to be secreted during the formation of new cuticle. The formation of the cuticulin membrane may be a useful model for studying the origin of membranes in general. It arises as a triple layer de novo and is not a modified plasma membrane. Growth is by accretion at the edges of patches of cuticulin which increase in area until they cover the new surface. The triple layer (i.e. three dense laminae) may develop striations about 30 Å apart transverse to the membrane, which perhaps form a sieve allowing small molecules to pass while protecting the cell from enzymes in the molting fluid. A similar porous structure persists in the tracheoles. After the resorption of molting fluid the triple layered structure again becomes obvious and the outermost layer separates from the other two to become what may be the surface lipid monolayer. The surface patterns in cuticle of various sorts probably arise by buckling of the cuticulin layer as it increases in surface area.     

Breeding Strategies in Females of the Parasitoid Wasp Spalangia endius: Effects of Mating Status and Size

Does the mating status or body size of a female parasitoid wasp affect her host size choice or propensity to burrow? In Spalangia endius, using smaller hosts appears to reduce a female's cost of parasitization but not her son's fitness. However, virgin females, which produce only sons, did not preferentially parasitize smaller hosts. Mated females also showed no host size preference. Mated females burrowed more than virgins in the presence of hosts, although not in their absence. Burrowing may reduce a mated female's harassment from males, and not burrowing may increase a virgin female's chance of mating because males avoid burrowing. Mating did not increase female longevity. Greater female size increased the offspring production of mated females burrowing for hosts but not in the absence of burrowing and not in virgin females. A female's size had no significant effect on whether her first drill attempt was on a large or a small host or on the duration of her successful drills.     

Courtship behaviour in Meraporus gramivticola (Hymenoptera) and other Pteromalinae

The courtship of Meraporus graminicola Walker is described and compared with that of other Pteromalinae. The sequence of courtship movements is characteristic of each species, and in all species studied the male's mating attempt is made not during a sequence of courtship movements but at the end of the sequence. Then the male extends its mouthparts, an action common to all species, and if there is no contact with the female's antennae a mating attempt follows.     

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.     

Design of an insect cuticle associated with osmoregulation: the porous plates of chloride cells in a mayfly nymph

In mayfly nymphs of the genus Coloburiscoides, cell complexes with an osmoregulatory function (so-called chloride cells) are found in the integuments of the oral gills, the abdominal gills and gill filaments, the coxae and the thoracic sternites. The cuticle overlying each cell complex is a rigid circular plate which is known to be porous to colloidal lanthanum suspensions. The present study shows that the plate is composed only of the cuticulin and dense layers of the epicuticle. Both layers have substructures built of subunits on almost perfect hexagonal lattices. The lattice spacings are 53 and 9.5 nm for the dense layer and the cuticulin layer respectively. During moulting the apical plasma membrane of the chloride cell remains adpressed to the old porous plate. The new porous plate is formed from a new chloride cell which intrudes from the base of the integument. Throughout the moult small pores persist in the new and otherwise continuous cuticle to allow continuity of the cytoplasm of the apical and basal portions of the old chloride cell. It is thought that this phenomenon allows osmoregulatory function of the chloride cell complex to be maintained during the moult.     

Cuticulogenesis correlated with ultrastructural changes in oenocytes and epidermal cells in the late cockroach embryo

During late embryogenesis in a cockroach, the epidermal cells secrete two cuticles: the embryonic cuticle and the pharate first larval cuticle. Late embryogenesis begins with the deposition of the cuticulin layer of the embryonic cuticle. The embryonic cuticle is an atypical one. It remains relatively thin and a well lamellated endocuticle is usually lacking. After general apolysis of the embryonic cuticle the epidermis secretes the epicuticle of the first larval cuticle and, subsequently, a typical lamellate procuticle. During the penultimate phase of late embryogenesis (i.e. before general apolysis) the epidermis becomes larvally committed. Some epidermal cells start to differentiate into specialized structures of the dermal glands, whereas the differentiated oenocytes appear to have acquired some stability. Nevertheless, shortly before general apolysis some oenocytes display signs of an increased alteration of the SER. When general apolysis occurs, the oenocytes contain a well-developed SER. The whole of the oenocyte population is programmed to regress after epicuticle deposition of the first larval cuticle. The correlation of oenocyte regression with available data on cuticulogenesis, ecdysteroid titres and cuticular lipid synthesis is discussed.     

The development of the female accessory gland in the insect Rhodnius prolixus

The specialized cell types and two distinct regions of the adult Rhodnius prolixus cement gland develop from a simple pseudostratified epithelial tube during the 20–22 days of the fifth stadium. Feeding initiates the first phase, proliferation. Cells round up and divide tangentially to the lumen. Following the proliferation phase, differentiative mitoses occur and differentiation, resulting in secretory units (consisting of a ductule, gland cell and cuticular lining), ensues in the distal region. Ductule morphogenesis occurs without pseudocilia, thus differing from other insect glands. The complex changes in cell shape and interaction occur during development of the secretory unit. The secretory cell and end-apparatus develop from a double cell unit at the base of elongating ductules. The inner cell produces a complex end-apparatus of epicuticle that mirrors the microvillar pattern and then it degenerates. The ductules are lined by cuticulin and inner epicuticle while the central gland lumen has a layer of endocuticle as well. The epithelium of the proximal region remains simple producing the thick corrugated cuticle characteristic of the adult secretory duct. The mesodermal covering forms a thick longitudinal striated muscle layer that adheres to the epithelium via desmosomes.     

The morphology of mating plugs and its formation in scorpions: Implications for intersexual participation

Mating plugs have been proposed as a mechanism that has evolved to avoid sperm competition. Their structure and composition vary across taxa and are related to the effectiveness of its function. This effectiveness could be related to different evolutionary interests of the sexes. Urophonius brachycentrus and Urophonius achalensis (Scorpiones, Bothriuridae) are highly suitable species to study mating plugs because both are monandrous species with specific morphological and physiological responses in the female's genitalia. Here, we analyze (a) the morphology and fine structure of the mating plugs of both species, (b) the site of production in males and the formation process of the mating plug, and (c) the changes that it undergoes over time in the female's reproductive tract. In both species, a complex mating plug obliterates the female's genital aperture and fills the genital atrium. We observed considerable interspecific variation in the mating plug morphology. A mating hemi-plug was found surrounding the capsular lobes of the hemispermatophore, which could have a mixed composition (involving portions of the hemispermatophore and glandular products). The glandular portion was transferred in a semi-solid state filling the female's genital atrium and then hardening. Changes that the plug undergoes in the female's genitalia (darkening and increase of the “distal” area of the plug) indicate a participation of the female to the formation of this type of plug. Our study provides new insights into the plugging phenomenon in scorpions, and we discussed the adaptive significance as a post-copulatory mechanism to avoid sperm competition.     

The hormonal coordination of cuticulin deposition and morphogenesis in Drosophila imaginal discs in vivo and in vitro

Cuticulin is the first layer of the insect cuticle to be deposited and is laid down as a continuous inelastic sheet over the apical surface of cuticle-secreting cells. During metamorphosis in Drosophila melanogaster, imaginal discs deposit the cuticulin layer of the pupal cuticle between 3 and 7 hr after puparium formation. This is a period of rapid morphogenesis involving cell shape changes and cell rearrangements. We have examined cuticulin deposition in vivo and in vitro with a view to understanding the coordination of cuticulin deposition with morphogenesis. We find that the optimum hormonal regimen (of the steroid hormone, 20-hydroxyecdysone) for the completion of both morphogenesis and cuticulin deposition in vitro parallels the changes in hormone titer observed in vivo. We also find that cuticulin is deposited last over cell boundaries, thereby allowing cell rearrangements to occur as cuticulin is laid down. We have identified in vitro conditions under which cuticulin deposition is completed precociously, inhibiting further morphogenesis. Cytochalasin B and colchicine do not inhibit cuticulin deposition and we therefore conclude that an intact cytoskeleton is not necessary for secretion of this extracellular structure. Finally, we present a preliminary protocol for the partial purification of cuticulin synthesized in vitro by mass isolated discs.     

Ultrastructure and development of single-walled sensilla placodea and basiconica on the antennae of the Sphecoidea (Hymenoptera : aculeata)

While the pore plates of some species of the Sphecoidea (Hymenoptera) rise above the antennal surface, those of other species are flush with it. Not all species possess pore plates. On the antennae of those species, which lack pore plates, small sensilla basiconica are found. The pore plates of Psenulus concolor were studied in detail. The cuticular apparatus rises above the antennal surface. Cuticular features are the encircling ledge and delicate cuticular ledges reinforcing the perforated plate, as well as a joint-like membrane that anchors the plate into the antennal cuticle. Each pore plate is associated with 9–23 sense cells and 4 envelope cells, the second of which is doubled. In very early developmental stages, however, supernumerary envelope cells are observed; they degenerate before the cuticulin layer is secreted. Envelope cell 1 secretes a temporary dendrite sheath, while the envelope cells 2–4 are responsible for the secretion of the cuticular apparatus.The morphology and the development of the small sensilla basiconica are described in Trypoxylon attenuatum. The curved sensillum pointing to the tip of the antenna is anchored by a joint-like membrane. About 15 sense cells innervate the sensillum. The number and the arrangement of the envelope cells resemble that of the sensilla placodea. During very early developmental stages, supernumerary envelope cells are also observed. They degenerate before the cuticle of the cone is secreted by the surviving envelope cells 2–4.