Fine Structure of the Female Intoshia variabili(Alexandrov & Sljusarev) (Mesozoa: Orthonectida)

The morphology and fine structure of female Intoshia variabili, new combination for Rhopalura variabiliAlexandrov & Sljusarev, 1992, were studied with transmission electron microscopy. The body surface is covered with a 3-layered cuticula, under which is a layer of ciliated + non-ciliated cells arranged in alternating rings around the body. Ciliated cells have lateral extensions that intercalate with the non-ciliated cells. The kinetosome of each cilium has two longitudinally oriented cross-striated rootlets. The outer surface of the ciliated cells is covered with small tubercles, and the cytoplasm of these cells contains granules, vacuoles, mitochondria, fibrillar structures and lamellary bodies. A band of dense fibrils passes through the upper part of each ring of cells, going from one cell junction to another, encircling the entire body. Between the layer of ciliated + non–ciliated cells and the oocytes, elongated contractile cells from 4–5 longitudinal columns and 1 ring, the latter at the level of ciliated rings 7–9. The contractile cells contain thick and thin longitudinally oriented fibrils. The oocytes contain a large nucleus, numerous mitochondria, electron–dense granules and 1–2 spherical structures. An anteriorly situated, ciliated goblet–like receptor, not described for any other orthonectids, consists of three closely apposed cells, the upper part of which contains densely packed cilia. The genital pore opens through a non–ciliated cell and is surrounded by several cells with granules.     

Muscle formation in the sexual genetation of Intoshia variabili (Orthonectida)

Muscle formation in Intoshia variabili (Orthonectida) has been studied in the course of development of the sexual (free-living) specimen. The muscle system originates in the early embryogenesis as a distinct continuous layer located between the outer cell layer and the inner cell mass. Later this cell layer disintegrates into separate muscle strips. The presence of a distinct muscle system in Orthonectida and the pattern of its development evidences for placing this group into Triploblastica rather than into Diploblastica.     

Nuclei in the plasmodium of Intoshia variabili (Orthonectida) as revealed by DAPI staining

DAPI staining of wholeamounts was used to reveal the parasitic plasmodium of the orthonectid Intoshia variabili in its host, the turbellarian Macrorhynchus crocea. The nuclei of the parasite differ drastically from those of the host in size, morphology, and the estimated DNA content. Our findings indirectly support the idea that the orthonectid plasmodium is a distinct parasitic organism, rather than modified host cells.     

Ciliary transition zone of the orthonectid Intoshia variabili

The ciliary transition zone is described in the orthonectid Intoshia variabili. The ciliary transition zone in this species corresponds to the long type of transition zones. Close proximity of orthonectids to Spiralia is discussed.     

Fine structure and development of the silver and golden cuticle in butterfly pupae

Pupae of the butterflies Danaus chrysippus and Helioconius charitonius display characteristic patterns of golden spots, while the pupae of the genera Euploea and Amauris exhibit metallic lustre over most of their surface; E. core and midamus more golden, A. ochlea and niavius more silvery. The absolute reflectance exceeds 80% at wavelengths longer than 550 nm, but drops more or less steeply at shorter wavelengths (shown by microspectrophotometry for E. core and A. ochlea; in all species this effect is caused by constructive interference of the incident light at Multiple Endocuticular Thin Alternating Layers (METAL cuticle). Dense, cuticular D layers alternate with clear, watery C layers and form over 200 double layers. The thickness of the D layers is fairly constant throughout the stack, whereas the C layers systematically increase and decrease in thickness, thus causing the broad bandwidth of the reflector. Connecting filaments, traversing the C layers in zig zag course, probably secure the mechanical stability of the arrangement. After drying, the C layers have vanished and the lustre is lost; the cuticle is now perfectly transparent, except for D. chrysippus, where it is partly transparent and partly yellow. The metallic reflectance develops between 20 and 30 hr after pupal ecdysis, starting with blue colours which change via green to gold or silver. About half a day before emergence of the imago, the reflection fades again via the opposite colour sequence. Coincident with these colour changes, the METAL cuticle is being deposited and decomposed, respectively. The deposition zone immediately above the apical epidermal microvilli consists of about three helicoidal lamellae as in normal, non-reflecting cuticle. The METAL cuticle is formed abruptly at the outer border of the deposition zone, possibly during condensation of the cuticular microfibres. The periodicity it is suggested is controlled either directly by the epidermal cells or indirectly via appropriate self-assembling processes.     

Fine structure of the chitin-protein system in the crab cuticle

The fine structure of the organic matrix of the shore crab cuticle (Carcinus maenas L.), observed in transmission electron microscopy, reveals three different levels of organization of the chitin—protein complex. The highest level corresponds to the ‘twisted plywood’ organization described by Bouligand (1972). Horizontal microfibrils, parallel to the cuticle plane, rotate progressively from one level to another. When viewed in oblique section this structure gives superimposed series of nested arcs, visible in light microscopy or at the lowest magnifications of the electron microscope, in all the chitin-protein layers. At the highest magnifications of the electron microscope and with the best resolution, when the ultrathin sections are exactly transverse to the microfibril, a constant pattern can be observed which consists of rods transparent to electrons, which are embedded in an electron-opaque matrix. In cross-section, these rods often form more or less hexagonal arrays. We call a microfibril one rod and the adjacent opaque material, and question the usual interpretation of the microfibril molecular structure. Between these two levels of organization, there is an intermediate level, which corresponds to the grouping of microfibrils. Microfibrils form a dense structure, with few free spaces in the membranous layer, the deepest and non-calcified layer of the cuticle. In other parts of the cuticle, microfibrils are grouped into fibrils of various diameters or form a reticulate structure, the free spaces of the organic matrix being occupied by the mineral.     

Fine structure of isolated fibrils from the cuticle of Lumbricus sp.

A method has been developed to isolate and purify cuticular fibrils of Lumbricus. Polarizing microscopy confirms the collagenous nature of the isolated fibrils. Study in the electron microscope of isolated fibrils, negatively or positively stained, shows that they are cylindrical, unbranching and without periodic structure. Enzymatic treatment of cuticles with alpha-amylase and trypsin results in a more or less complete dissociation of the fibrils which appear clearly to be made up of helically wound bundles of filaments (30-40 A). The biophysical data and compared to the ultrastructural organization of other periodically cross-banded fibrils.     

Studies on Pogonophora. 4. Fine structure of the cuticle and epidermis

The fine structure of the integument in several species of Pogonophora has been examined by electron microscopy. The cuticle over the main body is composed of several layers of orthogonally arranged fibres embedded in an amorphous matrix. It is regularly traversed by microvilli from underlying epidermal cells. Toothed bristles of the annuli and setae of the anchor are composed of closely packed fibrous cylinders wrapped in a cortical material. In fine structure the cuticle, setae, toothed bristles (or setae) and setal sacs forming the setae closely resemble the corresponding structures in annelids. The cuticle is maximally thick over the forepart (protosome + mesosome) ; it is very thin and non-fibrous over the surface of the metameric papillae and over extensive areas of post-metameric trunk. The possibilities of a collagenous nature of the cuticle fibres and their mode of secretion by the epidermal cells are discussed. The organization of various cell-types forming the epidermis over the entire animal is examined. Possible functions of these cell-types are discussed. Notable amongst these are 'possible zymogen cells' and some absorptive cells. The intriguing question of nutrition in these gut-less tubiculous animals is re-examined in the light of present observations.     

The tardigrade cuticle. I. Fine structure and the distribution of lipids

Fine structure and lipid distribution are studied in cuticles of five tardigrade species using TEM and SEM. Double osmication using partitioning methods reveals a substantial lipid component in the intracuticle and in irregular granular regions within the procuticle. These results are substantiated by the loss of osmiophily following lipid extraction with chloroform and methanol. Other lipid components are revealed by osmication following unmasking of lipo-protein complexes with thymol. These occur in the outer epicuticle and in the trilaminar layer lying between the epi- and intracuticles. Anhydrous fixation of dehydrated tardigrades (tuns) reveals dense, superficial masses of osmiophilic material, apparently concentrated lumps of the surface mucopolysaccharide ('flocculent coat'). However, cryo-SEMs of tuns reveal similar dense aggregations which apparently exude from pores (not visible) and are removed by chloroform. These results suggest extruded lipids since the flocculent coat is unaffected by chloroform; likely functions of such lipids are discussed.     

Fine structure of the cuticle of the desert scorpion, Hadrurus arizonensis.

The structure of the sclerite and intersegmental cuticle of the opithosoma of the desert scorpion, Hadrurus arizonensis, has been examined by transmission electron microscopy. The sclerite cuticle contains a four-layered epicuticle, a hyaline exocuticle, an inner exocuticle and an endocuticle. The outer part of the hyaline exocuticle and the whole of the inner exocuticle are constructed of helicoidally arranged planes of microfibrils. Within the endocuticle, the overall architecture is not helicoidal as previously assumed, but consists of bundles of microfibrils oriented horizontally and vertically. Microbibrils of the inner exocuticle and the endocutile are seen as simple unstained rods, but those of the hyaline exocuticle are electron dense rods with an unstained central core. The intersegmental cuticle contains a four-layered epicuticle and a procuticle. In detail, its fine structure differs in most respects from that of the sclerite cuticle. Electron microscopy reveals that hyaline exocuticle, previously assumed to be continuous from sclerite to intersegmental membrane, is absent in the latter.     

Fine structure of body wall cuticle of females of Meloidodera charis,Atalodera lonicerae,and Sarisodera hydrophila (Heteroderidae)

The body wall cuticle of adult females of Meloidodera charis, Atolodera lonicerae, and Sarisodera hydrophila is examined by transmission electron and light microscopy for comparison with Heterodera schachtii and previous observations of additional species of Heterodera, Globodera, and Punctodera. The cuticle of M. charis is least complex, consisting of layers A, B, C (with A outermost), and varies in overall thickness from 3 to 8 μm. As in other species, the cuticle is thickest in mature specimens. The cuticle of A. lonicerae is 6-9 μm thick; unlike M. charis it has an innermost layer, D, in addition to A, B, and C. The cuticle of S. hydrophila varies from 14 to 30 μm thick and includes a D layer similar to A. lonicerae; layer C is subdivided into additional zones relative to other heteroderids, and the external portion of the cuticle is infused with an electron-dense material. The presence of a D layer in A. lonicerae and S. hydrophila is a character state which is shared with Globodera spp. and Punctodera sp. The electron-dense material in the outer layers of S. hydrophila also occurs in Globodera spp. and Punctodera sp. On the other hand, H. schachtii resembles other Heterodera spp. as well as M. charis by the absence of a D layer and lack of electron-dense material in the outer layers. The pattern of occurrence of shared character states, including those of the cuticle, may be useful for phylogenetic analysis of Heteroderidae.     

Fine structure and development of the sperm of the tick Ornithodoros (Pavlovskyella) erraticus (Ixodoidea, Argasidae)

Sperm development in Ornithodoros (Pavlovskyella) erraticus includes the formation of subsurface cisternae in the primary spermatocytes, which divide meiotically to secondary spermatocytes and ultimately to spermatids. During spermiogenesis the spermatid undergo morphological transformation including polarization of the nucleus and subsurface cisternae, formation of a cisternal tube, and modification of the subsurface cisternae to cellular processes surrounded by cisternal vesicles. Further transformation occurs after spermatids are introduced into the female. The spermatid cisternal tube now invaginates to form an inner cord surrounded by an outer sheath. The invaginated inner cord elongates anteriorly as the outer sheath continues to invaginate posteriorly during spermiogenesis. With further elongation, the spermatid membrane ruptures anteriorly, leaving the inner cord exposed as the outer surface of the maturing sperm. Posteriorly, the original plasma membrane invaginates to form an acrosomal canal which becomes surrounded by an acrosome. The hemispherical anterior end of the mature sperm is covered with rows of projections separated from the remainder of the sperm by a row of fringed processes. Except for the posterior end, the rest of the sperm is covered by longitudinally distributed electron-dense cellular processes and an outer mat of more electron-lucent tubular elements. Mitochondria and bundles of microfibrils are found beneath the cellular processes. Microfibrils are suggested to be the principal contractile organelles responsible for sperm motility. Cellular processes appear to be the main external motile structures, while movements of tubular elements and fringed processes may also contribute to sperm motility.     

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.     

The structure of the cuticle of the scorpion Pandinus imperator (Koch)

Frozen and celloidin sections of the cuticle of Pandinus have been examined by means of phase contrast microscopy. The massive cuticle of the pedipalp, and the thinner cuticle of sterna and terga, show a random arrangement of fibres in the horizontal plane, whereas in the cylindrical podomeres of the legs the fibres are parallel and disposed along the length of the podomere. The laminae appear to be composed of horizontally arranged fibres, possibly associated with a laminar membrane. Curved continuous sheets of fibres pass from one lamina to the next through the interlaminar region.     

Fine structure and development of Pilosporella chapmani (Microspora: Thelohaniidae) in the mosquito, Aedes triseriatus (Say)

New information on the life cycle and fine structure of Pilosporella chapmani, a microsporidium of the mosquito Aedes triseriatus, is presented. Pilosporella chapmani is shown to have two sporulation sequences, one of them being involved in transovarial transmission. One sequence, involving meiosis and production of a moniliform sporogonial plasmodium, occurs in the larval fat body, resulting in eight uninucleate, spherical, and fully developed spores. The other occurs in oenocytes of adult mosquitoes and results in isolated, binucleate, elongate, and thin-walled spores. Also, for the first time, metabolic products are shown to be expelled into the surrounding host tissues through the wall of the sporocyst.