An electron-microscope investigation into the cuticle and associated tissues of the operculum of some marine serpulids

The fine structure of the opercula of Spirobis borealis Daudin and S. pusilloides Bush, and the primary and secondary operculum of S. granulatus (L) have been examined by electron microscopy. In different regions, the epithelium of the operculum exhibits variations in thickness and fine structure which correspond to transitions from peduncular to opercular wall to opercular plate epithelia. Externally, the peduncle and walls of the operculum are covered by a cuticle which is composed of several layers of fibrils/fibres embedded in an amorphous matrix. It is regularly traversed by microvilli from underlying cells. At the operculum rim, the cuticle changes so that its appearance is thick and solid. It continues across the roof of the operculum as a thin layer overlying a calcareous plate. The secondary operculum of S. granulatus differs from those of the other species in that an internal calcareous plate and solid cuticle line the roof of the operculum. It differs further in possessing an opercular pore. The possibilities are discussed of the cuticle fibrils/fibres of the peduncle and the opercular wall being collagenous in nature, and later being transformed to a solid tanned structure overlying a calcareous plate. The modes of secretion of the cuticle and calcareous plate by underlying cells are also discussed.     

Über Bau und Funktion der Kiemen und Lungen von Ocypode ceratophthalma (Decapoda: Crustacea)

Electron micrographs reveal great differences between the epithelial linings of gills and lungs in the air-breathing crab Ocypode ceratophthalma. According to the fine structure, the gills have a mainly osmoregulatory function; they exhibit a very active transporting epithelium characterized by a large number of mitochondria, branched microvilli, and basal labyrinth. Blood spaces in the shaft of the gills are lined by podocytes, suggesting ultrafiltration. The lungs are typical respiratory organs, lined by a thin epithelium covered by a thin cuticle.     

Integumental ultrastructure and color patterns in the iridescent copepods of the family Sapphirinidae (Copepoda: Poecilostomatoida)

The ultrastructure of the integument of the sapphirinid copepods was studied by scanning and transmission electron microscopy. Samples were collected between 1991 and 1993 by plankton-net tows from the subtropical and tropical waters of the North Pacific. In all the seven species examined of Sapphirina and Copilia, a structure with multilayered platelets was found in the epidermal cells of the dorsal integument of the male. Each platelet is a regular hexagonal prism. The platelets form a plate with honeycomb arrangement within each epidermal cell. Just ventral to the dorsal cuticle, 10 to 14 plates are located parallel to each other and to the cuticle. The mean diameter and thickness of the platelets measured between 1.0 and 1.8 m and 61 and 83 nm, respectively, for the four species. The specific coloration of seven species was examined with reflected and transmitted light. The iridescent color may be explained by the theory of multiple thin-layer interference in some species which are considered to have an ideal laminar structure, but for the other species, mechanisms from non-ideal systems, including pigment-thin layer interaction, may also be involved.     

Feinstruktur des Trichterepithels von Rhinomuraena ambonensis (Teleostei,Anguilliformes)

The ultrastructure of the funnel-like tubes of the olfactory organ in Rhinomuraena ambonensis was investigated by electron microscopy. Frontal sections of the tubes demonstrate a symmetrical arrangement of an inner epithelium, connective tissue, and an outer epithelium. The surface of each peripheral cell of the epithelia bears a system of small ridges which does not correspond with that of the adjacent cells. In case of a rectilinear course of the epithelial cell borders, numerous desmosomes are located along the cell membranes. The fine structure of the desmosomes was analysed. Number and size of the intercellular spaces increases with increasing depth of the epithelium cell layers. The fine structure of epithelial, basal and secretory cells is described. The outer region of each epithelial cell contains densely packed tonofilaments. The fine structure of sensory “buds” which are sparsely distributed within the outer epithelium of the funnels is described. The basal border of the epithelia consists of a rather thick basal membrane. Blood vessels, nerve bundles, chromatophores and storage cells with cristalline inclusions are embedded in the connective tissue. The fine structure of the chromatophores and storage cells is described. The importance of desmosomes, tonofilaments and intercellular spaces, as well as the basal membrane and the amount of collagen is discussed in relation to the reinforcement of the funnels.     

Surface morphology of dogfish (Scyliorhinus canicula) gill epithelium,and surface morphological changes following treatment with zinc sulphate: A scanning electron microscope study

The surface morphology of the gill epithelium of the dogfish Scyliorhinus canicula L. (collected near Barcelona, Spain, in February–March, 1981) was studied by scanning electron microscopy. Pavement cells exhibited either surface microvilli or microridges, which were randomly distributed on both the primary (afferent and efferent sides and interlamellar spaces) and secondary epithelium. Chloride cell apical regions on the afferent side displayed characteristics closer to freshwater than to marine teleosts: no apical pits were detected; chloride cells displayed longer microvilli than those of adjacent cells. Two morphologically different cell types were identified: a large chloride cell and a smaller cell (probably a chloride cell too), measuring 4 to 7 m and 1 m, respectively, the latter being dominant in the interlamellar spaces. Apart from pavement cells, the mucous cell was the prevalent cell type on the efferent region. The respiratory epithelium consisted of a mozaic of typical epithelial cells; some chloride and mucous cells were present, mainly located at the base of the secondary lamellae. Surface morphological changes were monitored after exposing the dogfish to subacute zinc treatment: 10 ppm Zn (ZnSO₄) for 3 wk. The chloride cell was the only cell type that underwent any modifications: microvilli became longer and tips were swollen following Zn treatment. The results are discussed in relation to a previous study on the effects of zinc sulphate on chloride cell response and heavy metal distribution in excretory organs of the dogfish.     

Fine structure of some prosobranch ospharadia

The fine structure of the osphradia of Buccinum undatum 1. three Hawaiian Conus spp., Nassarius reticulatus (L), Nucella lapillus (L) and Littorina littorea (L) was examined. There is a remarkable uniformity in the arrangement of ultrastructural cell types in all the ospharadia investigated. The marginal glandular region is characterised by a single layer of cells, bearing a regular pallisade of microvilli and including two types of mucous cell. The epithelium of the sensory region is several cells deep, and bears a complex layer of microvilli in many orientations. Besides indifferent cells it contains two types of cell bodies of ciliated nerve processes. One type ends at the surface of the sensory region. The other, containing an elaborate array of smooth membranes in the perikaryon, has a process which enters the transitional region between sensory and glandular areas. In the transitional region, specialised cells with motile cilia adjoin the glandular region, and similar, but unciliated cells, containing large pigment granules scattered throughout the cytoplasm, adjoin the sensory region. The distal surface of both cell types is dissected by elefts extending 2 to 3 proximally, then widening into extensive spaces which contain cytoplasmic processes. The ciliated neurites which enter the transitional region end in the spaces at the base of the unciliated transitional cell elefts. It is suggested that the neuroepithelial cell processes, both those distributed over the sensory region and those concentrated in the transitional region, are receptors.     

Structural organisation,transfer and biological fate of endosymbiotic bacteria in gutless oligochaetes

From differences in size and structure, it appears there are two species of gram-negative bacteria in the gutless oligochaetes Phallodrilus leukodermatus and P. planus from Bermuda. A non-random, differentiated and consisten distribution pattern of the extracellular bacteria along the length of the worm's body underlines the regulated nature of the bacterial colonization. This emerges also from studies on the transfer of the bacteria between host generations: exceptional for oligochaetes, eggs are deposited singly in a sticky mucus sheath and not together in a cocoon. They become infected immediately at oviposition, apparently by intrusion from large stores of bacteria in a genital pad abutting the female pores. During ontogenesis, a balance is established between extracellular, active bacteria and intracellular lytic forms enclosed in vacuoles by the epidermal cells. In early developmental stages, lytic bacteria prevail, but older worms harbour mainly extracellular prokaryotes underneath their cuticle. The thick epidermis/cuticle complex is differentiated in regular zones with a progressive trend towards enclosing and digesting bacteria intracellularly in the deeper layers. These are the first results on the transfer and biological fate of endosymbiotic bacteria living in animals from sulfide biotopes.     

Post-mating odor in females of the solitary bee, Andrena nigroaenea (Apoidea, Andrenidae), inhibits male mating behavior

We investigated odor changes and their behavioral significance in the solitary, ground-nesting bee Andrena nigroaenea. We used gas chromatography with electroantennographic detection and performed behavioral tests with males in the field using natural odor samples and synthetic compounds. We found that only cuticle extracts of young females elicited copulation attempts in the males. We demonstrated that among the 17 compounds which triggered electroantennographic responses, all-trans-farnesyl hexanoate and all-trans-farnesol were significantly more abundant in unattractive cuticle extracts of A. nigroaenea females. Dufour’s gland extracts of these females also contained greater amounts of both compounds. In bioassays using synthetic farnesyl hexanoate and farnesol we found that these compounds inhibit copulation behavior in the males. Farnesyl hexanoate is probably synthesized in Dufour’s gland and used by females for lining brood cells. We interpret the semiochemical function of farnesyl hexanoate and its precursor farnesol to have evolved secondarily. As an outcome of sexual selection, it facilitates the discrimination by males of receptive females from nesting and thus already mated individuals. The dual function of these compounds represents an elegant parsimony in the chemical communication system of this insect. Received: 19 January 2000 / Revised: 29 May 2000 / Accepted: 24 June 2000     

气态甲醛对大鼠肺组织影响的病理学观察

为了研究大鼠吸入甲醛后其肺组织病理结构的改变并探讨其损伤机理,以雌性Wisar大鼠为实验材料,采用动式吸入方式染毒15d(暴露组甲醛浓度32～37mg·m-3,每日暴露4h)后,取肺组织进行光镜及透射电镜观察.光镜观察结果表明,甲醛暴露后,大鼠肺组织主要表现为间质性肺炎和肺泡性肺炎的病理学特点,肺泡壁毛细血管扩张、充血、出血严重,个别区域可见大量炎细胞浸润,肺内细支气管和肺泡腔内见大量血细胞,部分肺泡腔内有透明膜形成,内含脱落的肺泡上皮细胞.电镜观察结果表明,甲醛暴露后,大鼠肺泡上皮细胞损伤严重,线粒体嵴断裂、肿胀、空泡化,部分肺泡上皮细胞胞膜溶解,细胞器丢失,细胞坏死、脱落.推测甲醛吸入可致大鼠肺病理损伤,损伤机理可能与自由基损害和醛糖还原酶(AR)表达变化有关.     

Studies on enzymes associated with calcification of the cuticle of the hermit crab Clibanarius olivaceous

In the anomuran Clibanarius olivaceous Henderson, the cuticle of the cephalic and thoracic regions is calcified, while that of the abdominal region is uncalcified. Histochemical observations have been made on the possible enzymes involved in the process of calcification of cuticle. The calcified regions show the presence of enzymes such as phosphorylase, alkaline phosphatase and carbonic anhydrase. The possible role of phosphorylase in calcification may be production of phosphoric esters, which form the required substrate for alkaline phosphatase. The latter appear to be associated with the production of phosphate ions from phosphoric esters. The carbonic anhydrase may be associated with the production of carbonate ions. The suggestion that these enzymes are involved in the process of calcification is further supported by experimental evidence of inhibition of the action of enzymes by enzyme inhibitors. The inhibition of enzymes leads to reduction in the amount of calcium added to the cuticle.This paper formed part of a thesis approved for the award of Ph. D. degree of the University of Madras.     

Symbiosis between bacteria and oceanic clonal sea star larvae in the western North Atlantic Ocean

Bacteria were present in the majority of clonal sea star bipinnariae (Luidia sp.) collected between June 1987 and August 1990 from oceanic populations in the subtropical western North Atlantic Ocean. Light and electron microscopy revealed dense aggregations of bacteria within lobes of the epidermal cuticle in the gastric region of larvae. Gram-negative rods and less-common elongate spiral bacteria were observed, always in close association with branching epidermal microvilli. Intact and partially digested bacteria occurred in vesicles and phagosomes within epidermal cells, a probable indication of phagocytotic activity by the host. The association of larvae of Luidia sp. and bacteria ranged widely on both geographical and temporal scales. During July and August 1988, larvae were abundant (1.6 to 11.1 m³) in the mixed surface layer (<10 to 100 m) of stations in the Gulf Stream, the Sargasso Sea and the North Equatorial Drift, and 96% (mean of 5 stations, n=8 to 10 larvae in each station) of the individuals surveyed harbored bacteria beneath their cuticle. In a single station on the Florida Current sampled during winter, spring, and summer months between 1989 and 1991, 79 to 90% of the larvae harbored bacteria. The incidence of symbiosis was higher in actively cloning larvae than in non-cloning larvae. This is the first documentation of a symbiosis in field populations of echinoderm larvae.     

On the nature and role of protein constituents of the cuticle of crustaceans in relation to permeability of the cuticle

The chemical composition of the cuticle in regions which are permeable and impermeable to water in 4 crustaceans (Ocypode platytarsis, Metapenaeus monoceros, Emerita asiatica, Ligia exotica) was investigated, with special reference to the protein components. It was found that the cuticle which is permeable lacks the outer epicuticle or the entire epicuticle compared to the cuticle in the impermeable regions. The permeable cuticle is distinguished by the absence of a fuchsinophil protein, which is a precursor of tanning. Permeability of the cuticle is also associated with the presence of a simple protein, positive to the biuret test, and with a protein containing sulphydryl groups. It is considered that the cuticle protein may play a role in conferring permeability properties to the cuticle itself.     

Association of filamentous epibacteria with Tubificoides benedii (Oligochaeta: Annelida)

A previously undescribed colonization of the marine oligochaete Tubificoides benedii (d'Udekum, 1855) from a sulfide-rich habitat by filamentous epibacteria was observed in 1984 and 1985. Electron microscopy showed that the bacteria were embedded in the cuticle of the posterior region of the worm. The association is apparently not pathogenic; possible forms of positive interaction are discussed.     

Epithelial immunity in a marine invertebrate: a cytolytic activity from a cuticular secretion of the American horseshoe crab, <Emphasis Type="Italic">Limulus polyphemus</Emphasis>

The cuticle of the American horseshoe crab, Limulus polyphemus, is largely free of the macroscopic epibionts that rapidly colonize most solid surfaces exposed to sea water. Here, we describe a viscous surface secretion that coats the carapace of the horseshoe crab. We report methods for stimulating production of the substance, identify hemolytic and liposome-permeabilizing activities and provide a partial biochemical characterization. We propose that this secretion functions as an anti-fouling agent protecting the chitinized epithelium of the cuticle from colonization by deleterious epibionts.     

Fine structure of naive and allogeneic challenged ampullae in Botrylloides subpopulation I from the Mediterranean coast of Israel

The external peripheral termini of vasculature in botryllid ascidians (ampullae) are important in the expression of effector mechanisms during histocompatibility reactions. We study here morphological changes to the microstructure during allorecognition in Botrylloides subpopulation I (SP1) from the Mediterranean coast of Israel, where special giant ampullae, called megaloampullae are developed hours after first allogeneic challenge. The basal part of each naive ampulla consists of a sheath of continuous squamous epithelial cells (1 μm×20 μm). At the tip of the ampullae, about 130 epithelial cells become columnar with wide apical pads (15 μm×5–10 μm), that contain electron-opaque “adhesive vesicles”. Foci of crystallizations were observed within the vesicles of some columnar cells. Ampullar epithelial cells develop internal folds that support tight attachments between circulating blood cells (most of them are pigment cells) and ampullar epithelium. During the histoincompatibility process, the tunic peripheral edge at the interaction area becomes highly convoluted. Filaments (up to 1.16 μm) accumulate in the interaction tunic matrix. Some of these filaments encircle destructed cells. Fragmented cell membranes are also found next to the reacting ampullae. The most characteristic feature of the Botrylloides SP1 rejection reaction is dilation of the ampullae. The ampullar epithelium becomes “curly” when megaloampullae are formed. Within the curly region, about 30% of the squamous epithelial cells are further stretched, up to 33 μm in length. Some additional mechanisms are suggested to explain the fast increase (up to seven times) in ampullar width that is recorded within a few hours from the first allogeneic contact.     

Homopteran chemical signatures reduce aggression of tending ants

Summary. Because generalist ants are aggressive towards foreign insects, the recognition of homopterans by tending ants is critical in ant/homopteran trophobiosis. Herein we report experimental evidence indicating that Argentine ant, Linepithema humile (Mayr) (Hymenoptera: Formicidae) learn to associate the production of honeydew with the chemical characteristics of homopteran cuticle, suppressing ant aggression and allowing the ants to tend homopterans. Although chemically-mediated associative learning is well understood in honeybee foraging, to our knowledge, it has not been reported before in ant/homopteran trophobiosis.     

Exfoliation of epithelial cells by the scallop Placopecten magellanicus : seasonal variation and the effects of elevated water temperatures

Previous studies have shown that large numbers of ciliated and nonciliated epithelial cells (diam.: 6 to 15 μm) are released by adult sea scallops, Placopecten magellanicus (Gmelin), during summer months in Newfoundland when water temperatures are at a maximum and gonads are well developed. Such exfoliation of cells could be a response to stresses associated with elevated water temperatures and/or spawning activity. In the present study an electronic particle counter/sizer was used to further investigate the factors that influence exfoliation of epithelial cells by juvenile and adult scallops throughout the year. We observed release of epithelial cells from juveniles, and from adults collected in months when gametogenic activity was minimal, indicating that exfoliation does not occur as a result of reproductive activity alone. SEM analysis revealed little difference in surface characteristics of the gills, mantle and gonad between scallops that had released cells and those that had not, suggesting that exfoliation of small numbers of cells may be a consequence of cellular turnover and normal physiological function. Adult scallops were monitored in a second experiment to determine the effects of raising water temperatures from 8.5 to 14.7 and to 21.0 °C on the frequency (proportion) and rate of cellular exfoliation. Only at the highest experimental temperature (21.0 °C) were exfoliation rates significantly higher than rates recorded at 8.5 or 14.7 °C. SEM analyses revealed some damage to gill, mantle and gonad tissues when scallops were exposed to 14.7 and then to 21.0 °C for a total of 8 d. Received: 21 August 1996 / Accepted: 13 September 1996     

Peribuccal organs ofPlacopecten magellanicus andChlamys varia (Mollusca: Bivalvia): Structure,ultrastructure and implications for feeding

In order to better understand the structure of bivalve peribuccal organs and relate this to existing functional paradigms of their role in feeding, the labial palps of two scallop species,Placopecten magellanicus from the Bay of Fundy, Canada (1985 and 1986), andChlamys varia from the Bay of Brest, France (1986), were examined using histological techniques and electron microscopy. The ridged palp surface displays a uniformly dense ciliation with relatively few mucocytes; these are essentially concentrated in the region of the secondary ledge and may, through their secretory activity, determine the fate of particle masses in this area. The mucus secretions of the ridged palp surface are qualitatively different from those of the smooth palp surface. Mucocytes are much more abundant on the smooth palp surface, where it is suggested that their homogeneous secretions attenuate the potentially adverse effects of anteriorly-directed cleansing and swimming currents. Two other cell types are found in the palp epithelia: ciliated cells, which are very numerous on the ridged surface and relatively rare on the smooth surface, and non-ciliated epithelial cells, which are very numerous on the smooth surface and rare on the ridged surface, where they are confined to the palp margin. In addition to the mechanical role of the ciliated cells and mucocytes, the ultrastructural characteristics of the ciliated and non-ciliated epithelial cells indicate a dichotomy of function between the ridged and smooth surfaces. The ridged surface epithelial cells present an ultrastructural specialization in the absorption of dissolved and colloidal matter, suggesting an accessory nutritive role, whereas the smooth surface simple epithelial cells show signs of active molecular synthesis. No specialised sensory cells were observed on the ridged surface; it is therefore not yet possible to conclude whether the labial palps are capable of selection based on individual particle characteristics.