Exoskeletal structure in the Ordovician trilobite Flexicalymene

Scanning Electron Microscope study of the exoskeletal ultrastructure of secondarily phosphatized material of Flexicalymene sp. from the Upper Ordovician Maquoketa Shale, Iowa, USA, shows that the exocuticle, comprising 20% of the total exoskeletal thickness, is composed of horizontal laminar units between 0.2 and 1 μm thick. These units consist of primarily mineralized organic fibres which form horizontal laminae interconnected by inter-laminae. The endocuticle is considerably more mineralized than the exocuticle, and its original organic structure cannot be observed in untreated preparations. Etching with chromium sulphate reveals: (1) horizontal organic laminar units, 0.2 to 2 μm thick, and (2) pore canals with non-twisted walls about 0.3 μm in diameter. Exuvia cannot be distinguished from the exoskeletons of dead animals. The exoskeletal ultrastructure in trilobites agrees essentially with that in crustaceans.     

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.     

Observations on the integument of the water mite Arrenurus major (Acari: Parasitengona)

A study of the integument of the aquatic mite Arrenurus major Marshall is presented. When the cuticle is examined with the unaided eye and the light microscope, it appears to possess numerous tiny pits. However, scanning electron micrographs of the cuticle reveal that it is a solid surface with topographical sculpturing of the epicuticle, indicating that the “pits” are an internal phenomenon. In cuticle which has been sectioned, areas devoid of cuticular material beneath the thin exocuticle are revealed. These areas are the pits which are goblet-shaped. The integument consists of five major strata. These are from the outside to the inside: (1) a superficial layer with a maximum observed thickness of 725 Å, (2) an epicuticle with a thickness of about 900 Å and composed of at least four sublayers, (3) an exocuticle with a thickness of about 1.5 Å. Fibers of the exocuticle are arranged in a Bouligand pattern and exhibit a regularly occurring discontinuity with a spacing of 200 Å. (4) An endocuticle ranging from 15 to 20 μ in thickness. The endocuticle is characterized by bandings which superficially resemble the lamellae of insects but are not homologous, microfibers which exhibit a preferred orientation, and the presence of the pits; and (5) an epidermis lying beneath the endocuticle and extending into the pits. Pore canals are present only in the exocuticle and have their origin at the apices of the pits. The pore canals contain a central filament, and a plug is present just beneath the epicuticle.     

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.     

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.     

中华稻蝗受精囊的显微与超微结构

在显微及亚显微水平上研究了中华稻蝗受精囊的结构。该结构由外向内依次为：围脏膜,肌肉层,结缔组织,基膜,上皮层和内膜层。其中内膜层又分为上表皮,外表皮和内表皮三层,其间可见许多分泌小管。上皮层分别由锥形分泌细胞和长柱形细胞组成,前者内含大量的分泌泡。肌肉层由环肌和纵肌构成,其中环肌比较发达。     

An ultrastructural study of the larval integument of the midge,Chironomus riparius meigen (Diptera: Chironomidae)

Summary The larval integument of the midge, Chironomus riparius Mg., is unusually thin although it conforms with the normal insect pattern. The cuticle of the post-cephalic segments is about 3 m thick and overlies an epidermis which has an irregular basal plasma membrane resulting in spaces occurring between it and the basement membrane. The ventral tubuli have a similar epidermis but the cuticle is somewhat thinner. The anal papillae have the thinnest cuticular covering with a uniquely folded epicuticle of variable thickness, and their epidermis has the characteristics of a transporting epithelium. No evidence of pore canals could be found in the cuticle of any part except the head capsule which has a remarkably smooth epicuticle and a distinct layer which may represent the exocuticle. There are no spaces between the basement membrane and basal plasma membrane of the epidermis in the head. Ultrastructural evidence would suggest that gaseous exchange can occur across most of the post-cephalic integument.The author is indebted to Mrs. L. Rolph and Mr. R.L. Jones for their technical assistance     

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.     

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.     

The transfer of lipid in insects from the epidermal cells to the cuticle

The structure of the pore canals and the tubular filaments they contain are described in a series of insects and types of cuticle. In all these cuticles the tubular filaments arise from the plasma membrane of the epidermal cells and they contain argentaffin material, regarded as sclerotin precursors, and lipid-staining material, regarded as wax precursors. These materials are transferred to the inner epicuticle and are exuded over the surface of the outer epicuticle to form the waterproofing layer as described in the preceding paper. They are also transported to those parts of the endocuticle destined to form hard exocuticle. There are no terminations of tubular filaments in the soft cuticle of Manduca larva, in the soft expanding cuticle of Rhodnius, and in the non-sclerotized post-ecdysial endocuticle of Tenebrio. Apis. etc. In the puparium of Calliphora lipid appears to be added by the epidermal cells directly and not by way of tubular filaments. It is confirmed that lipid is a component of sclerotized cuticle.     

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.     

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.     

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.     

Fine structure of the respiratory organs of the Climbing perch, Anabas testudineus (Pisces: Anabantidae)

An electron microscopic study has been made of the three respiratory organs of climbing perch. The gill structure is similar to that of the other telcosts but the thickness of the water/blood barrier is much greater, being as great as 20 μm in some specimens. The increased thickness is due to a multilayered epithelium which is thinner (3.5–7 μm) over the marginal channel of the secondary lamellae. The other two main layers, basement membrane and pillar cell flange, are relatively thin (about 1 μm).
The pillar cells have a typical structure, but in certain regions they are contiguous with one another and line well-defined blood channels. Some of the columns of basement membrane material in such regions may be common to adjacent pillar cells.
The air-breathing organs are (a) the lining of the suprabranchial chambers , and (b) the labyrinthine plates attached to the dorsal region of branchial arches. Electron microscopy showed that their structure is well adapted for gas exchange, the air/blood barriers being only 0.12–0.3 μm, comprising an epithelial layer, basement membrane, and thin capillary endothelium. The many parallel blood channels of the respiratory islets of both organs are separated by pillar-like structures which differ from the pillar cells of the secondary lamellae. Thus the hypothesis that the air-breathing organs represent modified gills is not supported by this study.
The fine structure of the non-respiratory region of the air-breathing organs is similar to that of the skin, and includes chemoreceptor-like cells. Evidence concerning the possible homology of pillar cells with plain muscle cells is discussed.     

Ultrastructural shape and three-dimensional organization of the intracuticular canal systems in the mineralized cuticle of the green crab Carcinus maenas

Two main self-contained canal systems are present in the crab mineralized cuticle. The first, or fibre canal system, is constituted by simple, unbranched vertical canals containing axially running fibres in close association with myoepidermal junctions. The second, or pore canal system, is composed of procuticular pore canals and epicuticular channels that prolong the procuticular canals. In opposition to widespread opinion, pore canals make up a three-dimensional branched system extending from the apical plasma membrane of the epidermis up to the epicuticle. Branching occurs by projections of lateral horizontal from the vertical canals at the lower level of the pigmented layer and by innumerable ramifications of epicuticular canals. In agreement with Neville's model for insects, vertical procuticular pore canals of crustacean mineralized cuticle, and also fibre canals, exhibit a twisted ribbon structure reflecting the helicoidal arrangement of the horizontal chitin-protein microfibrils.     

Structure and development of spines over the skin surface of the river puffer Takifugu obscurus (Tetraodontidae,Teleostei) during larval growth

The histological structure and development of spines on the skin surface of Takifugu obscurus were studied during larval development conducted artificially with an average 30‰ salinity and 18.0–20.3°C water temperature. The epidermis comprises an outermost layer, middle layer, and the stratum germinativum, and contains three types of gland cells: small spherical or flask‐shaped mucous cells, larger sacciform mucous cells, and large granular cells. The dermis and subcutis follow. The spines first appear over the ventral region at 10 days after hatching and consist of two parts: a central long tapering portion which projects into the epidermis and eventually outside of the body, and a short supporting basal portion that is embedded within the stratum compactum layer of the dermis. The central, long tapering portion has two very short processes on top until 25 days after hatching, but these two separate spines fuse into one 30 days after hatching. In contrast, the short supporting spines rooted at the base consist of three to six small spines (usually four to five spines) and are present even in the adult stage. Therefore, calcareous spines consisting of one central long spine and three to six smaller supporting spines form tetra‐ and septaradiate spines (mainly penta‐ and hexaradiate). The spines first appear over the ventral region.     

The structure of integument and wax glands of Phenacoccus fraxinus (Hemiptera: Coccoidea: Pseudococcidae)

Using scanning electron microscopy and optical microscopy,we studied the structure of the integument and wax glands of the mealybug,Phenacoccus fraxinus Tang(Hemiptera:Coccoidea:Pseudococcidae).We observed the ultrastructure of four wax pores including trilocular,quinquelocular,and multilocular pores as well as tubular ducts,recording characteristics of their structure,size and distribution.We found that that the integument of the mealybug consists of three main layers-the procuticle,epidermis and basement membrane-and four sub-layers of the procuticle-the epicuticle,exocuticle,endocuticle and formation zone.The waxsecreting gland cells were closely arranged in epidermis.All of them were complex and composed of one central cell and two or more lateral cells.These complex cells possess a large common reservoir for collection and storage.Synthesized by the glandular cells,the wax is excreted outside integument through canals.     

The ultrafine structure of the body wall of sexually mature thorny-headed worms Echinorhynchus gadi (Acanthocephala)]

Studies of the fine structure of the adult acanthocephalan Echinorhynchus gadi have given a new information on the structure and organization of the body wall of these parasitic helminths. Their body surface is covered by glycocalyx of mucopolysaccharide nature. Just under it there is the surface membrane which has numerous invaginations forming a network of branching canals from which membrane vesicles are isolating. In their turn these canals pass through "the cytoplasmic canals" of the cortical matrix. Between the surface membrane and cortical matrix there is the base plate. These three structures form the striped layer underlain by the felt layer. It is formed by three layers of fibrous strands (one circular and two longitudinal), which are parallel to the body surface. These strands consist of loosely laid fibrils. The lowest layer is a radial one which occupies 2/3 of the body wall. It consists of the radial strands beginning from the cortical matrix and ending at the basement membrane. Numerous lipid droplets and glycogen granules are formed here. Two types of fibrils with 0.26 and 0.05 diameter have been detected for the first time. The radial layer in the cytoplasm was found to have crystalline structures and polymembrane bodies, numerous nuclei with light karyoplasm and distinct nucleoli. The location of the nuclei is of two types: either in the cytoplasm or in the "lacunae". We have shown that the "lacunae" are specialized sites of the cytoplasm whose boundaries are marked by the fibres of two types. Besides, this type of the acanthocephalan was found to have two "giant lacunae" extending along the body.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cuticle structure and systematics of the Macrobiotidae (Tardigrada, Eutardigrada)

The cuticle of tardigrades is characterized by three main layers: epicuticle, intracuticle and procuticle. Pillars are present in the epicuticle of almost all heterotardigrades, but these structures are also known in a few species of eutardigrades. The apparent heterogeneity of the cuticular ultrastructure in several species of the Macrobiotidae (Eutardigrada) prompted us to analyse the structure of the cuticle in this family. Eleven species in several genera were investigated with light and/or electron microscopy. All the species of the genera Murrayon and Dactylobiotus showed pillars in the epicuticle, whereas the examined species of Macrobiotus , Richtersius and Xerobiotus completely lacked pillars. Therefore, in the Macrobiotidae, in contrast to what appears with light microscopy, the cuticle is homogeneous within each genus examined at the electron microscopic level. Considering the absence of pillars in the Macrobiotidae a synapomorphy, we propose the erection of two new subfamilies. Macrobiotinae subfam. n. is characterized by the absence of pillars in the epicuticular layer and includes, in addition to the genera Macrobiotus, Xerobiotus and Richtersius, the genera Pseudohexapodibius, Adorybiotus, and probably also Minibiotus, Calcarobiotus and Pseudodiphascon . Murrayinae subfam. n. is characterized by the presence of pillars in the epicuticular layer and includes the genera Murrayon, Dactylobiotus and, probably, Macroversum.