Chitinous cuticle and systematic position of tardigrada

The chitinous nature of the cuticle, jaws and stomodaeum of three species of Tardigrada has been definitely proven using a specific micromethod involving a preparation of purified chitinase. These chemical characteristics are in favour of the phylogenetic closeness between Tardigrada and the Arthropoda.     

A freeze-fracture study of the surface of the infective-stage larva of the nematode Trichinella

The surface layers of the cuticle of the infective, first-stage larva of the nematodes Trichinella spiralis and T. spiralis var. pseudospiralis have been studied by means of the freeze-fracturing technique. No obvious differences between the two nematodes were found. A double-layered structure covers the cuticle. Its outermost layer consists of particles embedded in an amorphous matrix; its inner layer is composed of a sheet of fine filaments which may be composed of globular subunits. This unique double layered structure is not like a normal cell membrane in structure. The surface of the cuticle beneath it is relatively smooth except for impressions from the inner surface of the double-layered structure. The cuticle surface did not fracture in the manner of a cell membrane.     

Ultrastructural localization of tyrosinase in the tardigrade cuticle

Tyrosinase activity has been demonstrated ultra-structurally in the cuticle of the eutardigrade Macrobiotus hufelandi. The enzyme could be localized in the outer layer (=epicuticle) of the integument. A weak deposition of reaction product was also seen in the cytoplasm of storage cells, free floating in the haemolymph.     

角质层的离析及显微观察方法

植物角质层的离析方法很多,获取化石植物的角质层可以同时用几种化学处理方法。舒氏液浸解是最常用的方法,也是几种方法共用时最关键的步骤。浸解液浓度过大或处理时间过长有可能破坏角质层的结构。对于已经获取到的角质层,利用相差光学显微技术可以增加反差。利用微分干涉光学显微技术不仅反差增加,而且有立体感,背景颜色也可以调节。荧光显微分析技术在不破坏标本的前提下,可以获取到表皮的特征。扫描电子显微镜具有观察不透明物体,放大范围广以及高的分辨力等优越性,可作为光学显微镜的必要补充。     

The stabilization of locust cuticle

Cuticle from the metathoracic femur of adult locusts (Locusta migratoria) is characterized with respect to changes in water content and in protein extractability during maturation. The swelling behaviour and extractability of fully-sclerotized cuticle are compared to those of chemically-modified, unsclerotized cuticle.It is concluded that although dehydration may contribute to the stabilization of cuticle, it cannot account for the observed differences. The properties of mature cuticle can best be explained by the assumption that covalent cross-links are present between protein molecules.     

Scanning electron microscopy studies of cuticle micromorphology in Cycas L. (Cycadaceae)

Abstract

A scanning electron microscopy (SEM) study of Cycas cuticle characteristics was undertaken in order to expand our knowledge of microscopic characters not observable under light microscopy and to clarify unresolved affinitites among some species within the genus. Whole leaf and isolated cuticle specimens from the middle region of leaflets of greenhouse-grown plants of Cycas revoluta, Cycas rumphii, Cycas circinalis, Cycas media, and Cycas normanbyana were examined using SEM for interior and exterior features. Characteristics in common include hypostomy, hair bases on abaxial and adaxial surfaces, adaxial cells randomly arranged, adaxial exterior cuticle smooth, and stomata sunken to various degrees but stomatal pit always formed by two layers of epidermal cells. Stomatal complex is of the polyperigenous type. Stomata randomly dispersed and oriented, and except C. revoluta, are not contiguous. Stomata deeply sunken in C. revoluta, intermediate in C. rumphii and C. normanbyana, and less sunken in C. circinalis and C. media. Aperture between guard cells extends the entire stomatal length in C. rumphii and C. normanbyana, ～80% in C. circinalis and C. media, and ～50% in C. revoluta. Cuticular features of C. revoluta show the greatest difference from the other species in complex relief of exterior cuticle and interior cuticular structure of subsidiary cells; C. media and C. circinalis show close similarity to each other and their stomatal complex dimensions fall within the same unique cluster using principal component analysis under normalized variables. C. normanbyana and C. rumphii show the most similarity to each other in cuticular micromorphology. Stomatal complex dimensions of these two species fall into a second cluster that also includes C. revoluta. These data contrast with current taxonomy placing C. normanbyana synonymous to C. media.     

A new form of insect cuticle

A hitherto unnoticed, harder form of cuticle, which occurs on the mandibles of the Australian plague locust, Chortoicetes terminifera , is described     

An overview on plant cuticle biomechanics

Plant biomechanics combines the principles of physics, chemistry and engineering to answer questions about plant growth, development and interaction with the environment. The epidermal-growth-control theory, postulated in 1867 and verified in 2007, states that epidermal cells determine the rate of organ elongation since they are under tension, while inner tissues are under compression. The lipid cuticle layer is deposited on the surface of outer epidermal cell walls and modifies the chemical and mechanical nature of these cell walls. Thus, the plant cuticle plays a key role in plant interaction with the environment and in controlling organ expansion. Rheological analyses indicate that the cuticle is a mostly viscoelastic and strain-hardening material that stiffens the comparatively more elastic epidermal cell walls. Cuticle stiffness can be attributed to polysaccharides and flavonoids present in the cuticle whereas a cutin matrix is mainly responsible for its extensibility. Environmental conditions such as temperature and relative humidity have a plasticizing effect on the mechanical properties of cuticle since they lower cuticle stiffness and strength.The external appearance of agricultural commodities, especially fruits, is of great economic value. Mechanical properties of the cuticle can have a positive or negative effect on disorders like fruit cracking, fungal pathogen penetration and pest infestation. Cuticle rheology has significant variability within a species and thus can be subjected to selection in order to breed cultivars resistant to pests, infestation and disorders.     

New molecular data for tardigrade phylogeny, with the erection of Paramacrobiotus gen. nov.

Up to few years ago, the phylogenies of tardigrade taxa have been investigated using morphological data, but relationships within and between many taxa are still unresolved. Our aim has been to verify those relationships adding molecular analysis to morphological analysis, using nearly complete 18S ribosomal DNA gene sequences (five new) of 19 species, as well as cytochrome oxidase subunit 1 (COI) mitochondrial DNA gene sequences (15 new) from 20 species, from a total of seven families. The 18S rDNA tree was calculated by minimum evolution, maximum parsimony (MP) and maximum likelihood (ML) analyses. DNA sequences coding for COI were translated to amino acid sequences and a tree was also calculated by neighbour-joining, MP and ML analyses. For both trees (18S rDNA and COI) posterior probabilities were calculated by MrBayes. Prominent findings are as follows: the molecular data on Echiniscidae (Heterotardigrada) are in line with the phylogenetic relationships identifiable by morphological analysis. Among Eutardigrada, orders Apochela and Parachela are confirmed as sister groups. Ramazzottius (Hypsibiidae) results more related to Macrobiotidae than to the genera here considered of Hypsibiidae. Macrobiotidae and Macrobiotus result not monophyletic and confirm morphological data on the presence of at least two large groups within Macrobiotus. Using 18S rDNA and COI mtDNA genes, a new phylogenetic line has been identified within Macrobiotus , corresponding to the ' richtersi-areolatus group'. Moreover, cryptic species have been identified within the Macrobiotus ' richtersi group' and within Richtersius . Some evolutionary lines of tardigrades are confirmed, but others suggest taxonomic revision. In particular, the new genus Paramacrobiotus gen. n. has been identified, corresponding to the phylogenetic line represented by the ' richtersi-areolatus group'.     

Effect of sample treatment on biomechanical properties of insect cuticle

Experimental limitations often prevent to perform biomechanical measurements on fresh arthropod cuticle samples. Hence, in many cases short- or long-term storage of samples is required. So far, it is not known whether any of the standard lab-techniques commonly used to fix or store insect cuticle samples in any way affects the biomechanical properties of the respective samples.In this paper we systematically address this question for the first time, with a focus on practical, easily accessible and common lab-methods including storage in water, ethanol, glutaraldehyde, freezing and desiccation. We performed a comprehensive and sensitive non-destructive Dynamic Mechanical Analysis (DMA) on locust hind leg tibiae using a three-point-bending setup. Our results show that from all tested treatments, freezing samples at −20 °C was the best option to maintain the original values for Young's modulus and damping properties of insect cuticle. In addition, our results indicate that the damping properties of locust hind legs might be mechanically optimized in respect to the jumping and kicking direction.     

Spermatozoa in the reproductive system of a hermaphroditic marine tardigrade,Orzeliscus belopus (Tardigrada: Arthrotardigrada)

Orzeliscus belopus has long been regarded as the only hermaphroditic marine tardigrade, yet there has been no published detailed information on its internal anatomy. Our study elucidates the ultrastructure of the ovotestis and the spermatozoa of Orzeliscus cf. belopus from Bermuda. The ovotestis had no septum to separate male and female germ cells and, while early stages of spermatogenesis were not observed, many spermatozoa were found at the periphery in both anterior and posterior areas of the gonad. The nucleus and the mitochondria of the spermatozoa in the ovotestis extend backward from the centriole region, forming a half-headed arrow-shape with the nucleus on the outer side of the ‘arrowhead’. The cross section of a long vesicular body (the paranuclear vesicle) is dumbbell- or horseshoe-shaped and attached to almost the entire length of the nucleus. In the seminal receptacle, we found both a complete spermatozoon and some which started to degrade. There is an indication that sperm is further modified after discharge as within the receptacle duct the sperm is no longer half-headed arrow-shaped but has a straight nucleus. This modification might be correlated with the degeneration of the paranuclear vesicle. Our observations clearly show that O. belopus is a simultaneous hermaphrodite, and suggests that the reproductive mode includes copulation and cross-fertilization.     

Freeze-fracture of frog slow tonic fibers. Structure of surface and internal membranes

Slow frog fibers from frog cruralis were examined by freeze-fracture and compared with twitch fibers. Major differences in membrane architecture between slow and twitch fibers are in the shape and disposition of T tubules, the shape of junctional regions, the frequency of peripheral couplings and of Ca pump particles. Aggregates of ACh receptors on the surface membrane are distinguishable from peripheral couplings on the basis of size and shape of intramembranous particles.     

Temperature dependence of the electrical resistance of hornet cuticle: A statistical model

The electric resistance to d.c. of the yellow strips in the cuticle of worker hornets was measured in the dark under temperature changes within the optimal range of activity outside the nest (10–32°C). A distinct inverse correlation was observed between the resistance and the temperature, the former decreasing with rise of the latter. In all, each individual hornet measured was subjected to four successive cycles of measurement during which the specimens underwent warming followed by cooling. A slight unidirectional rise in the resistance both during warming and cooling was observed between two successive cycles. A typical thermal hysteresis loop formed between the warming and cooling lines, thus suggesting a memory effect.     

The cuticle of the hoplocarid crustacean Squilla desmaresti Risso

The cuticle of Squilla desmaresti does not show a well-defined Balken structure as described by Krishnakumaran (1956) in S. holoschista . Parallel fibres follow curved courses of differing orientation in the horizontal plane, and successive layers of fibres are separated by laminar membranes of different chemical composition from the remainder of the cuticle.     

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.     

Soil tardigrade biodiversity with the description of a new eutardigrade genus and its phylogenetic position

Sixteen tardigrade species have been identified from a total of 943 specimens isolated from 69 positive soil samples collected in southern Spain (Andalusia, Huelva). Three genera (Hexapodibius, Xerobiotus and the new genus Sarascon) and eight species are new records for the Iberian Peninsula, increasing Iberian tardigrade biodiversity by 6%, and 10 species are new records for soil habitats, increasing soil tardigrade biodiversity by 9% (from 96 to 108 species). A newly discovered species and genus are described, followed by an analysis and discussion of the species' phylogenetic position and synapomorphies, based on morphological and total evidence (morphology and molecular – 18S and 28S rRNA – data combined) phylogenetic analyses. The new genus is distinguished from other Itaquasconinae genera, to which it is phylogenetically related, by having a Parascon buccopharyngeal apparatus and Ramajendas claws. In contrast to general eutardigrade evolution, which is primarily determined by claw morphology, itaquasconid evolution is more related to buccopharyngeal apparatus morphology, which shows homoplastic evolution at superfamily, family and subfamily levels, and also defines functional trophic groups in soil-related environments.

http://zoobank.org/urn:lsid:zoobank.org:pub:068B9D87-27E2-4B26-8920-FF03CEF9869A     

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.     

Sclerotin and lipid in the waterproofing of the insect cuticle

In all the cuticles studied waterproofing is effected by extracuticular material, a mixture of sclerotin precursors and lipids, exuded from the tubular filaments of the pore canals. In Rhodnius larval abdomen it is a layer of thickness similar to the outer epicuticle, believed to be composed of 'sclerotin' and wax, in Schistocerca larval sternal cuticle and in Carausius sternal cuticle it is similar. In Tenebrio adult sternal cuticle of the abdomen, in both the extracuticular exudation and the contents of the distal endings of the tubular filaments, the wax component is obscured by hard 'sclerotin'. In Manduca larva a very thin layer of 'sclerotin' and wax is covered by an irregular wax layer, average 0.75 micron, twice the thickness of the inner epicuticle. In Periplaneta and Blattella the abdominal cuticle is covered by a soft waxy layer, often about 1 micron thick, which is mixed with argentaffin material. Below this is a very thin waterproof layer of wax and 'sclerotin' continuous with the contents of the tubular filaments, which is readily removed by adsorptive dusts. In Apis adult abdominal terga free wax plus sclerotin precursors form a thin layer which is known to be removed by adsorptive dusts. In Calliphora larva there is a very thin layer of the usual mixed wax and sclerotin and below this a thick (0.5 micron) layer, lipid staining and strongly osmiophil, likewise extracuticular and exuded from the epicuticular channels. This material (which is often called 'outer epicuticle') has the same staining and resistance properties as the true outer epicuticle on which it rests. In the abdomen of Calliphora adult the waterproofing wax-sclerotin mixture forms a thin layer over the entire cuticle including the surface of the microtrichia. There is also a thin detachable layer of free wax on the surface.     

Freeze-fracture observations of unfertilized and fertilized hamster oocytes with special reference to the use of lipid probes

Membrane and cytoplasmic changes were observed after in vitro fertilization of hamster oocytes by examining freeze-fracture replicas. The density of intramembranous particles on areas of membrane between microvilli increased following fertilization. Although the intramembranous particle density of microvilli is higher than that on the intermicrovillar membrane of unfertilized eggs, it did not change significantly after fertilization. Cytoplasmic changes in the Golgi complex and mitochondria upon fertilization indicate a change in cellular activity. Lipid binding probes were applied to the oocyte membranes in order to study the distribution of specific lipids before and after fertilization. Probes included the B-hydroxy-steroid complexing molecules, filipin and tomatin, and an anionic lipid binding antibiotic, polymyxin B. Both tomatin and filipin complex with steroids in the P and E faces of the plasma membrane (including the polar bodies), cortical granules and vesicles deeper in the cytoplasm, and the Golgi complex, leaving mitochondria, pronuclei, endoplasmic reticulum, and the majority of vesicles unlabeled. Polymyxin B binding is dependent on its application before or after fixation or in association with EGTA. With its application we detected both minor membrane perturbations of wrinkles and particle redistributions and major perturbations of vesicle fusions, the formation of blebs, and the loss of membrane morphology. Neither the distribution nor apparent quantity of these probes changed overall following fertilization, but this impression does not include specific sites of sperm-egg fusion.