Ultrastructural studies on the microfilaria of Cardianema sp. Alicata, 1933 (Nematoda; Onchocercidae)

The ultrastructure of the sheath, cuticle and hypodermis of the microfilaria of Cardianema sp, is described from electron micrographs of in utero- and blood-stages. The trilaminiar sheath invests the microfilaria throughout development in utero and it acquires a superficial coat after the microfilaria enters the blood stream of its reptile host. The cuticle consists of external and internal cortex, fibrillar and subfibrillar layers. The cuticle is attached to the hypodermis without the intervention of a basal lamina. The structure of the external cortex is modified in the annular furrows in the cuticle. The cellular hypodermis forms a complete subcuticular layer, although over much of the circumference the cells exist as thin cytoplasmic processes and where these overlap there are extensive tight junctions. The case for classifying the microfilaria of Cardianema a first stage larva is advanced and a functional but speculative, role for the sheath is proposed.     

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     

Anatomy and ultrastructure of the marine oligochaete Tubificoides benedii (Tubificidae), with emphasis on its epidermis-cuticle-complex

Although Tubificoides benedii (d'Udekem, 1855) (= Peloscolex benedeni) is a ubiquitous form in eutrophicated or polluted coastal muds and is characterized by an exceptional viability in sulphide sediments, almost nothing is known about its anatomy and the structure of its conspicuously papillate body surface. As a part of a research project on sulphide annelids, done by our group, we investigated the body structure of this common and still extraordinary marine tubificid using light, scanning and transmission electron microscopy.While the internal structures correspond to the general pattern of marine tubificids (Giere, 1983), the epidermis-cuticle-complex is unusual. The epidermis cells, which are much interdigitated, contain numerous extremely long and irregularly shaped mitochondria. At the tip of the body, many sensory cells, embedded in the normal epidermis cell layer, end with ciliary tufts at the body surface. Long epidermal microvilli traverse the thick cuticular layer which only in the anterior- and posterior-most segments is studded by epicuticular projections. From most parts of the body these surficial rodlets, so far held typical for all Oligochaeta, are absent. Instead, here the cuticle forms numerous high, almost leaf-life papillae between which a viscous mucus layer regularly harbours many bacteria.This distinct papillate body armature may serve for stabilization of the mucus layer with its associated bacteria. It is well conceivable that the mucus, beside its usual role of reducting friction in the burrowing process, attracts bacteria. That their settlement may be more than an accidental association and involve some regulative interaction is indicated by the specific attachment of gram-negative bacterial threads often populating the posterior end of T. benedii (Dubilier, 1986). The significance of possible stress exerted by the sulfide-environment on the worm, as evidenced by an unusually high concentration of lysosomal structures and abnormally formed mitochondria in the epidermis, has to be verified in further studies.     

Ultrastructure of an integumental organ with probable sensory function in Paragordius varius (nematomorpha)

The cuticle of late parasitic stages of Paragordius varius (Leidy, 1851) is composed of a layer with large fibres and a second layer (often named the areolar layer) distal from it. In this paper, organs are described that start at the basal side of the epidermis, pass the epidermis and the fibrous layer of the cuticle and merge with large, cushion‐like structures in the distal layer of the cuticle. The epidermal part of the organs is composed of darkly stained cells, which are probably in contact with the basi‐epidermal nervous system. Up to four processes of this cell traverse the cuticle. These processes might include cilia, because they contain microtubule‐like structures. The probable connection to nerve cells and the connection to the cushion‐like structures in the outer cuticular layer make it likely that the organs described here are sensory in function.     

昆虫足的吸附机制

自然界中有许多昆虫足上都有吸附垫,这些垫子经过进化能吸附在各种表面上,并能在运动中控制吸附力。昆虫吸附垫要么是光滑的表皮垫子,要么是密布特殊的刚毛。昆虫这种“飞檐走壁”的能力来自于粘液、复杂机械系统以及生物系统之间的相互作用。文章主要参考国内外研究昆虫吸附机制的文献,综述了能在光滑表面上行走的昆虫的基本爬行原理,对其吸附机制进行了分类。并分析目前研究的主要内容,提出目前昆虫吸附机制要解决的问题。最后对吸附机制在仿生机械应用上作了展望。     

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.     

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.     

Review of the ultrastructure of the nematode body cuticle and its phylogenetic interpretation

The phylogenetic interpretation of the nematode cuticle ultrastructure is reviewed within the framework of recent DNA-sequence data. In particular, the structure of the median and basal zones is discussed. Several structural elements of the cuticle seem to have arisen independently several times within the Nematoda and thus are highly homoplasious (e.g. the cortical or basal radial striae, spiral fibre layers and a fluid matrix with struts). Moreover, identifying the homology of the nematode cuticle ultrastructures is often very difficult at deep taxonomic levels. Hence, the cuticle appears to be unreliable regarding resolution of deep-level relationships in the Nematoda. However, at less inclusive taxonomic levels (e.g. families, genera, ...) the cuticle seems to be a more reliable phylogenetic marker.     

Structure of the egg funiculus and deposition of embryonic envelopes in a crab

The newly laid egg of Carcinus maenas is attached to a maternal ovigerous seta by a funiculus which consists of the two superimposed vitelline envelopes 1a + 1b, highly stretched and concurrently showing important structural alterations. The funiculus is glued to the specialized seta merely owing to the strong adhesiveness of its external face comprising the outermost vitelline envelope 1a, without any added adhesive. The subjacent envelope 2, originated from the cortical reaction, is not involved in such a funiculus elaboration. In the course of the embryonic development, four new coatings are successively secreted from the ectodermal embryonic cells, underneath the (1a + 1b + 2) fertilization envelope or embryonic capsule. They will remain until hatching in this concentric order, thus giving evidence of successive embryonic moulting cycles, with apolysis but without exuviation. In addition, the successive secretory phases, regarding to the embryonic envelope elaborations, happen in presence of high concentrations of the ecdysteroid ponasterone A which might be involved consequently in such secretory processes.     

Ultrastructure of the body wall of three species of Grania (Annelida: Clitellata: Enchytraeidae)

De Wit P., Erséus C. and Gustavsson L.M. 2011. Ultrastructure of the body wall of three species of Grania (Annelida: Clitellata: Enchytraeidae). —Acta Zoologica (Stockholm) 92 : 1–11. The body wall of three species of Grania, including the cuticle, epidermis and the musculature, are studied using TEM. The cuticle is similar to previously studied enchytraeids, with an orthogonal grid pattern of collagen fibers. This pattern is also seen in Crassiclitellata, which has been suggested as the sister taxon of Enchytraeidae. Variation of epicuticular and fiber zone patterns seen in Naididae (formerly Tubificidae and Naididae) seem to be lacking in Enchytraeidae. The fiber thickness, however, varies between Grania species and may be a phylogenetically informative character. The epidermis consists of supporting cells, secretory cells and sensory cells. Basal cells, typical for Crassiclitellata, were not observed. The clitellum of Grania seems to consist of two types of gland cells, which develop from regular epidermal tissue. It is possible that more cell types exist in different regions of the clitellum, however. The body wall musculature is arranged somewhat differently from that of closely related taxa; this refers to the reduction of circular and outer, triangular longitudinal muscle fibers, while the inner, ribbon‐shaped longitudinal muscle fibers are well‐developed. A search was conducted for the cause of the peculiar green coloration of Grania galbina De Wit and Erséus 2007, and it was concluded that neither cyanobacteria nor epidermal pigment granules were present in the fixed material.     

Diflubenzuron-Induced alterations during in vitro development of Tenebrio molitor pupal integument

The effects of diflubenzuron (DFB) in Tenebrio molitor pupae were first investigated on cuticle secretion induced by 20-hydroxyecdysone in vitro. The sternal integuments were treated by DFB either 3 days before culture or during culture. DFB, when applied before culture, did not prevent the molting hormone from inducing a new cuticle deposition by integument explants in vitro. However, this cuticle showed several architectural alterations and a thickness reduction. When applied during the culture in the presence of 20-hydroxyecdysone, DFB at high dose (≥ 20 μg/ml) was able to inhibit cuticle secretion, but lower doses (? 10 μg/ml) resulted in epicuticle deposition. These observations confirm in vivo studies showing antagonistic effects of DFB and ecdysteroids at the level of epidermal cells. In another series of experiments, the DFB effects were analyzed without addition of exogenous molting hormone in vitro. Because it had been observed in previous studies that pupal epidermal explants of Tenebrio secrete low but significant amounts of ecdysteroids in the culture medium, this in vitro secretion was measured by radioimmunoassay after DFB treatment. It was observed that DFB, when applied either before or during culture, significantly reduced the hormonal secretion in vitro. This reduction, observed at the level of epidermal cells, could be homologous with the diminution of the endogenous ecdysteroid peak previously described after in vivo DFB treatment in Tenebrio pupae.