Comparative ultrastructure of the pharynx simplex in turbellaria

Summary The simple pharynges in thirteen species of Turbellaria in the orders Macrostomida, Haplopharyngida, Catenulida, and Acoela have been studied by electron microscopy. After consideration of the functional aspects of the pharynx simplex, the relationship of the pharynx simplex ultrastructure to the phylogeny of the above mentioned groups is analyzed.The Haplopharyngida and Macrostomida are united as a group by the following characters: a pharynx transition zone of 1–5 circles of insunk cells with modified ciliary rootlets or no cilia, pharynx sensory cells without stereocilia collars and with a variable number of cilia, a prominent nerve ring with more than 30 axons circling the pharynx at the level of the beginning of the pharynx proper distal to the gland ring, 2 or more gland cell types in the pharynx, with at least two layers of muscle present and the longitudinal muscles derived from regular and special body wall circular muscles and a prominent post-oral nerve commissure. This specific arrangement can be distinguished from the other pharynx simplex types and is called the pharynx simplex coronatus.The catenulid pharynx simplex is characterized by the lack of a prominent nerve ring, no prominent post-oral commissure, a transition zone with epidermal type ciliary rootlets, recessed monociliated sensory cells, and one or no type of pharynx gland cell. The Acoela are specialized because of the epidermal type rootlets in the pharynx proper. They also lack a transition zone and a prominent nerve ring and have monociliated sensory cells different from the catenulid type.Ultrastructural characters of the pharynx simplex support the view that the Haplopharyngida-Macrostomida are monophyletic. The more primitive catenulid pharynx probably arose from a common ancestral pool with the Haplopharyngida and Macrostomida, although it does not appear possible presently to establish a clear monophyletic line for these forms. The various pharynx types within the Acoela appear to indicate independent origins with no clear link to the basic pharynx simplex type in the three other orders.Abbreviations Used in Figures a nerve axon - ar accessory rootlet - bb basal body - bn brain-nerve ring commissure - c caudal rootlet - ce centriole - ci cilium - cm circular muscle - cp ciliary pit - cu cuticle - cw cell web - d dictyosome - dp proximal pharynx proper cell - e epidermis - er rough endoplasmic reticulum - f fibrous rod - g gastrodermis - gc gastrodermal gland cell - he heterochromatin - i intercellular matrix - lc lateral nerve cord - lm longitudinal muscle - m mitochondria - mo mouth - mt microtubules - mv microvilli - n nucleus - nr nerve ring - ns neurosecretory granules - p pharynx proper - ph pharynx - po post-oral commissure - r rostral rootlet - rm radial muscle - s sphincter - sc sensory cell - sj septate junction - sr sensory rootlet - t transition zone - u ultrarhabdite - v vertical rootlet - va food vacuole - za zonula adhaerens - 1 type I gland cell - 2 type II gland cell - 3 type III gland cell - 4 type IV gland cell - 5 type V gland cell - 6 type VI gland cell - 7 type VII gland cell     

Die Rezeptoren an den ersten Antennen vonLeptestheria dahalacensis Rüppel (Crustacea,Conchostraca)

Zusammenfassung Bei dem ConchostracenLeptestheria dahalacensis kommen auf den ersten Antennen etwa 600 gleich aussehende Sinneshaare vor, die in Gruppen von jeweils 25–30 zusammengefaßt sind. Diese Sinneshaare sind in zwei Teile gegliedert, die durch das lichtmikroskopisch gut sichtbare Basalstück (basal bead) voneinander getrennt sind. Dieses bildet die Basis des Haares, dessen Wand im wesentlichen aus Epicuticula besteht. Apikal wird das Haar durch das Endkügelchen (terminal pellet) abgeschlossen. Das Basalstück wird von der untersten Lage der Epicuticula gebildet. Die 4–10 Receptorcilien, die jeweils einzeln ebensovielen Dendriten aufsitzen, ziehen aus dem inneren Teil des Rezeptors, der von insgesamt 5 Hüllzellen umgeben wird, durch das Basalstück, in dem sie stark eingeengt werden und verzweigen sich dann im äußeren Teil des Rezeptors. Sie ziehen bis zum Endkügelchen, in das sie durch einen Porus, den man als Häutungsporus ansprechen kann, eintreten. In der Häutungsvorbereitung wird der Haarbalg von der Hüllzelle 5, das Basalstück von der Hüllzelle 4, der Haarschaft dagegen von der Hüllzelle 3 gebildet. Dabei spaltet sich die Hüllzelle 3 ringspaltförmig auf, so daß in diesem Spalt der neuangelegte Haarschaft handschuhfingerförmig eingestülpt liegt. Die Hüllzelle 2 formt die Spitze des neuen Haares, während die Dendritenscheide von der Hüllzelle 1 abgegeben wird.

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The receptors on the first antennae ofLeptestheria dahalacensis Rüppel (Crustacea, Conchostraca)

Summary On the antennulae ofLeptestheria dahalacensis (Conchostraca) nearly 600 sensory setae of one type are found. They are gathered in groups of 25–30. The single sensory seta is divided into two parts by the basal bead which is easily visible in the light microscope. The basal bead is the socket of the seta, whose wall is mainly built up by the epicuticle. The terminal pellet closes the tip of the seta. The basal bead is derived from the innermost layer of the epicuticle. 4–10 dendrites each with one receptorcilium innervate the receptor. The receptorcilia stretch through the interior part of the receptor and the basal bead into the exterior part, where they branch. They enter the terminal pellet in a porus, which seems to be a moulting porus. The interior part of the receptor is surrounded by 5 sheath cells. During the premoult it becomes obvious, that the socket of the seta is built by the sheath cell 5, the basal bead by the sheath cell 4 and the shaft by the sheath cell 3. For this the sheath cell 3 is divided into two parts. Between this two parts the newly formed cuticle is invaginated. The sheath cell 2 formes the tip and the sheath cell 1 the cuticular sheath of the new bristle.

     

Ultrastructure of the epidermal maxilla II-gland of Scutigera coleoptrata (Chilopoda, Notostigmophora) and the ground pattern of epidermal gland organs in Myriapoda

The epidermal maxilla II-gland of Scutigera coleoptrata was investigated using light and electron microscopy. The glandular epithelium surrounds a spacious integumental cavity at the base of the maxilla II. The gland is formed as a compound gland organ that is composed of thousands of epidermal gland units. Each of them consists of four different cell types: a secretory cell, an accessory or intermediary cell, and a proximal and distal canal cell. The intermediary and the two canal cells form a conducting canal. Only in the most distal part of the intermediary cell is the canal lined by a cuticle. In the area of the two canal cells, the conducting canal is completely covered by a cuticle. The canal passes through the cuticle and opens into the spacious integumental cavity, which serves as a secretion reservoir. The structural organization of the epidermal maxilla II-gland was compared to that of other compound epidermal gland organs in Chilopoda and Diplopoda. All these glandular organs in Myriapoda share the same ground pattern.     

Ultrastructural investigation of the nuchal organs of Pygospio elegans (Polychaeta)

Summary The differentiation of the dorsal organs as well as the structure of the nuchal organs and their relation to the central nervous system in adult Pygospio elegans were studied by electron microscopy and compared to the nuchal organs of the larvae. The nuchal organs are represented by paired ciliary bands on the dorsal side of the first setiger, delimiting a median caruncle that is completely filled with epidermal and nervous tissue. They are composed of ciliated supporting cells and bipolar primary sensory cells constituting the nuchal ganglia, which are integrated into the brain. Microvillus-like processes of the ciliated cells give rise to a secondary covering layer over the sensory epithelium. The size of the nuchal organs is a sexually dimorphic feature.Dorsal organ formation is concomitant with the onset of sexual maturation in the male sex only. They appear as metameric ciliary bands on the dorsal side of the anterior body region and consist of ciliated cells accompanied by lateral accumulations of tubular gland cells. In the gametogenic segments they are structurally associated with the male genital pores and may be involved in reproduction. The results refute previous theories that dorsal organs are sensory and have a common origin to nuchal organs.Abbreviations ac anterior commissure of the brain - ace anterior circumesophageal connective - bb basal body - bl basal lamina - c cuticle - ca caruncle - cc ciliated cell - ci sensory cilium - co microvillar cover - d septate desmosome - db dorsal blood vessel - dn dorsal nerve cord - ea efferent axons - ec epidermal cell - eg elementary granules - g Golgi complex - i filamentous inclusion - lm longitudinal muscles - ly lysosome - mc motile cilia - mv microvillus - n neuron - ng nuchal ganglion - nn nuchal nerve - nu nucleus - oc olfactory chamber - pa palp - pc posterior commissure of the brain - pce posterior circumesophageal connective - rer rough endoplasmic reticulum - sI setiger I - sb sensory bulb - sc sensory cell - sd sensory dendrite - ser smooth endoplasmic reticulum - tf tonofilament bundle - v clear vesicles - za zonula adherens     

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.     

An ultrastructural analysis of the cuticle,epidermis and esophageal epithelium of Eisenia foetida (Oligochaeta)

The epidermis of Eisenia is covered by a cuticle and rests on a basement lamella. The cuticle, which is resistant to a variety of enzymes, is composed of non-striated, bundles of probable collagen fibers that are orthogonally oriented and are embedded in a proteoglycan matrix. The basement lamella consists of striated collagen fibers with a 560 Å major periodicity. Proximity and morphology suggest that the epidermis may contribute to both the cuticle and the basement lamella — that is, the single tissue may synthesize at least two types of collagen. The epidermis is a pseudostratified epithelium containing three major cell types (columnar, basal and gland) and a rare fourth type with apical cilia. The esophagus is lined by a simple cuticulated epithelium composed predominantly of a single cell type, which resembles the epidermal columnar cell. Rare gland cells occur in the esophageal epithelium, but basal cells are lacking.     

Adhesive organs of the gastrotricha

Summary Adhesive organs of 17 gastrotrich species of the order Macrodasyida and 2 species of the order Chaetonotida (Chaetonotida-Paucitubulatina) can be seen by transmission electron microscopy to comprise two gland cell types. These cells are morphologically similar to viscid and releasing glands of the Turbellaria and so are identified by these same names; the adhesive system in these gastrotrichs is therefore called a duo-gland system considered at least functionally comparable to the duo-gland organs of turbellarians. The two gland cell types project their necks through tubiform extensions of the animal's cuticle. Some adhesive tubules have only one of each gland type; others, even in the same species, may have two viscid and one releasing glands; and compound organs such as posterior footlike appendages may have three and four viscid glands and one releasing gland per tubule. Gland cells in some species have fibers, evidently cytoskeletal in function. The adhesive tubules are quite similar in all of these species and provide few characters for determining within-group relationships of the gastrotrichs. The duo-gland system of the Gastrotricha is probably not homologous with that of the Turbellaria.Abbreviations Used in Figures cu cuticle - ep epidermal cell - f fiber - la lateral adhesive organ - m muscle - pa posterior adhesive organ - rg releasing gland - sc sensory cilium - scb sensory cell body - vg viscid gland This research was supported by NSF grants DEB-77-06058 (S. Tyler, P.I.) and GB 42211 (R.M. Rieger, P.I.)     

Cytology of various antennal setae in a troglobitic Mysidacea (Crustacea)

Summary The various antennal setae can be differentiated from each other by the number and the type of their dendrites and by the cuticular structure of their external parts; these features correspond to functional differences. Moreover, the work revealed differences in relation to the corresponding setae of a marine Mysidacea previously studied by Guse (1978). Various hypotheses linking the ultrastructural differences to those that characterize the environments in which these two species live can be put forward.Abbreviations A1, A3 simple setae A1, A3 - An antenna - B1, B2 setulate setae B1, B2 - Bi bifid seta - bp bending plane - c1, c2, c3 type 1, 2, or 3 cilia (outer dendritic segments) - cu cuticle - d1, d2, d3 type 1, 2, or 3 dendrites (inner dendritic segments) - ec enveloping cell - g Golgi apparatus - h helically arranged cuticle - md microtubule doublet - n nucleus - p apical pore - r ciliary root - s setules - sc scolopale - scc scolopale cell - Si sickle-shaped seta - sm small seta - st stopper - t extracellular matter tube     

Immunocytochemical localization of choline acetyltransferase and muscarinic ACh receptors in the antenna during development of the sphinx moth <Emphasis Type="Italic">Manduca sexta</Emphasis>

Immunocytochemistry with monoclonal antibodies was used to investigate the locations of muscarinic acetylcholine receptors (mAChR) and choline acetyltransferase (ChAT) in sections of the developing antennae of the moth Manduca sexta. The results were correlated with a previous morphological investigation in the developing antennae which allowed us to locate different cell types at various stages of development. Our findings indicated that the muscarinic cholinergic system was not restricted to the sensory neurons but was also present in glial and epidermal cells. By day 4–5 of adult development, immunoreactivity against both antibodies was present in the axons of the antennal nerve, and more intense labeling was present in sections from older pupae. At days 4–9, the cell bodies of the sensory neurons in the basal part of the epidermis were also intensely immunolabeled by the anti-mAChR antibody. In mature flagella, large numbers of cells, some with processes into hairs, were strongly labeled by both antibodies. Antennal glial cells were intensely immunolabeled with both antibodies by days 4–5, but in later stages, it was not possible to discriminate between glial and neural staining. At days 4–9, we observed a distinctly labeled layer of epidermal cells close to the developing cuticle. The expression of both ChAT and mAChRs by neurons in moth antennae may allow the regulation of excitability by endogenous ACh. Cholinergic communication between neurons and glia may be part of the system that guides axon elongation during development. The cholinergic system in the apical part of the developing epidermis could be involved in cuticle formation.This work was supported by grants from the Natural Sciences and Engineering Research Council of Canada (NSERC), the Canadian Foundation for Innovation, and the Nova Scotia Research and Innovation Trust to P.H.T. and a NSERC postdoctoral fellowship to J.C.     

The ultrastructure of the so-called olfactory setae on the antennula ofDaphnia magna Straus (Crustacea,Cladocera)

A group of nine sensory setae is found on the tip of the antennula ofDaphnia magna in both sexes. Inside a seta four dendrites are situated, each with one receptor cilium. The receptor cilia extend through a liquor space into the exterior part of the seta. The exterior part of the liquor space is divided from the interior part by a knob-like thickening of the innermost layer of the epicuticle, the basal bead. The basal bead narrows the liquor space and the receptor cilia. The interior part of the liquor space is surrounded by five sheath cells, the exterior part by a thin cuticle. In the exterior part the receptor cilia branch partly and reach a terminal pellet on the tip of the seta. The terminal pellet is a thickened part of the epicuticle. It is permeable to several dissolved substances. It is the exterior part of the receptor that projects over the tip of the antennula and seems to be the entire seta. During the premoult the fifth sheath cell builds up the articulation of the seta, the fourth the basal bead, and the third the shaft of the seta. The first sheath cell forms the cuticular sheath. The organ seems to be a chemoreceptor, but the adequate stimulus is as yet unknown.     

Introvert,mouth cone,and nervous system of Echinoderes capitatus (Kinorhyncha,Cyclorhagida) and implications for the phylogenetic relationships of Kinorhyncha

Summary The introvert, mouth cone, and nervous system of Echinoderes capitatus were examined by transmission and scanning electron microscopy. The introvert bears seven rings of primarily quincunxial sensory scalids, including type 1 and 2 spinoscalids as well as trichoscalids; the latter two types are additionally provided with glandular cells. The mouth cone bears one ring of decamerous sensory oral styles and three rings of quincunxial sensory pharyngeal styles. The intra- to basiepithelial, bilateral nervous system consists of a circumentric nerve ring in the introvert, a terminal and proximal nerve ring in the mouth cone, a ventral chain of ganglia, one in each trunk zonite, and a caudal ganglion. The introvert, the neck, and the trunk zonites are innervated from the forebrain; the mouth cone and the pharyngeal bulb are innervated from the hindbrain. The monophyly of the Kinorhyncha is based upon the following autapomorphic characters: (1) a mouth cone, (2) a neck with 16 placids, (3) a trunk with 11 zonites, (4) scalids of three types: type 1 and type 2 spinoscalids, and trichoscalids, (5) an anteriormost ring of ten type 1 spinoscalids (sensory organs divided into a basal and a terminal part), (6) a posteriormost ring of 14 trichoscalids (glandular sensory organs which are undivided), (7) rings in between the anteriormost and posteriormost are type 2 spinoscalids (glandular sensory organs divided into a basal and a terminal part), (8) a mouth cone with a terminal and a proximal nerve ring, (9) nine sensory oral styles with decamerous symmetry (the dorsal style is missing) and (10) three rings of sensory pharyngeal styles with, from anterior to posterior, ten, five, and five styles with quincunxial arrangement. The following characters are assumed to be autapomorphic for the taxon Nematoda+Gastrotricha+Kinorhyncha+Loricifera+Priapulida: (1) a basiepithelial circumentric brain and (2) a neuropileous nerve ring in a subterminal position. The following characters are assumed to be autapomorphic for the taxon Kinorhyncha+Loricifera+Priapulida: (1) a neuropileous nerve ring in a terminal position, (2) an introvert with scalids, (3) an eversible foregut and (4) tanycytes.The unpublished doctoral thesis of B. Neuhaus [1991 Zur Ultrastruktur, Postembryonalentwicklung und phylogenetischen Verwandtschaft der Kinorhyncha. PhD thesis. University of Götingen, Germany] was finished simultaneously with the completion of this study.     

Morphology of the prothoracic discs and associated sensilla of Acanthocnemus nigricans (Coleoptera, Acanthocnemidae)

The Australian ‘little ash beetle’ Acanthocnemus nigricans (Coleoptera, Cleroidea, Acanthocnemidae) is attracted by forest fires. A. nigricans has one pair of unique prothoracic sensory organs and it has been speculated that these organs may play a role in fire detection. Each organ consists of a cuticular disc, which is fixed over an air-filled cavity. On the outer surface of the disc, about 90 tiny cuticular sensilla are situated. The poreless outer peg of a sensillum is 3–5 μm long and is surrounded by a cuticular wall. One ciliary sensory cell innervates the peg. As a special feature, the outer dendritic segment is very short already terminating below the cuticle. A massive electron-dense cylindrical rod, which most probably represents the hypertrophied dendritic sheath, extends through the cuticular canal connecting the tip of the outer dendritic segment to the peg. The dendritic inner segment and the soma are fused indistinguishably. Thin, leaflike extensions of glial cells deeply extend into that conjoint and considerably enlarged compartment which also contains large numbers of mitochondria. In summary, the sensilla of the sensory disc of A. nigricans represent a new type of insect sensillum of hitherto unknown function. The possible role of the prothoracic sensory organ in fire detection is discussed.     

Morphological basis of cardiac glycoside sequestration by Oncopeltus fasciatus (Dallas) (Hemiptera: Lygaeidae)

Summary The integument of Oncopeltus fasciatus is made up of a vacuolated and a pigmented epidermal cell layer. This double layered integument is present from late embryo to adult in male and female animals reared on milkweed or sunflower seeds. Experiments with a labelled glycoside as well as retrograde ink injections suggest that O. fasciatus concentrates cardiac glycosides, normally derived from the host plants, within the vacuolated epidermal cell layer throughout its life cycle. In the adult, droplets of glycoside-rich fluid appear at precise points along the dorsolateral margins when external pressure is applied to the thorax and abdomen. This pressure causes separation of cuticular flanges in the metathoracic epimeral lobe and rupture of the cuticle in restricted areas in the mesothorax and abdomen. In addition the pigmented epidermal cell layer and the distal membranes of the vacuolated epidermal cell layer rupture with the result that the contents of the vacuolated cell layer are eliminated onto the surface of the animal where they are retained as discrete droplets by the cuticular morphology. Release of cardiac glycosides into the haemolymph is prevented by a thick basal lamina on the haemolymph side of the vacuolated epidermal cells. No specialized muscles involved with fluid release were observed. The vacuolated epidermal cells do not show ultrastructural features characteristic of actively transporting tissues, i.e., abundant mitochondria and elaborate membrane infoldings. This suggests that glycoside sequestration is essentially a passive process and should not be associated with any physiological cost. Large concentration gradients of cardiac glycosides are maintained across the basal lamina, basal plasma and vacuolar membranes of the vacuolated epidermal cell layer. Possible mechanisms by which O. fasciatus is able to concentrate cardiac glycosides as well as the possible function of this phenomenon are discussed.Abbreviations A abdominal trabeculum - Ap mesofurcal apodeme - C metathoracic supracoxal lobe - D metathoracic stink gland duct - E metathoracic epimeral lobe - Ep pigmented epidermal cell layer - Ev vacuolated epidermal cell layer - G last thoracic ganglion - H haemocoel - M midgut - N nerve cord - P second phragma - R reproductive organ - T trachea - V dorsal vessel - W wing - bl basal lamina - c cuticle - cf cytoplasmic fragments - cv coated vesicle - d hemidesmosome - ep epidermal cell - en endocuticle - ex exocuticle - f flange - fp foot processes - gc glycoside compartment - h hair - is intersegmental region - id ink deposits - l lumen of metathoracic stink gland - m mitochondria - mb mushroom bodies - mt microtrichia - n nucleus - p pigment granule - s slit - sp spine - tsm tergosternal muscle - v vacuole     

Complex epidermal organs of Phascolion (Sipuncula): insights into the evolution of bimodal secretory cells in annelids

The epidermal organs of an undescribed Phascolion species from the Balearic Islands were investigated using SEM, TEM, LM, CLSM and μCT methods. We found axial receptor cells confirming the previously assumed sensory function of epidermal organs. Our analyses also revealed six types of secretory cells. Some secretory cells types are capable of secreting filamentous and amorphous secretion in two different ways simultaneously (bimodal secretion). The high diversity of cell types, the complex pattern of acinar units, and the absence of a common gland pore make epidermal organs of Phascolion unique amongst sipunculans (Phascolion type). Our reconstruction of the evolution of the epidermal organs of Sipuncula revealed that Phascolion‐type epidermal organs may have derived from either Golfingia‐, Sipunculus‐ or Phascolosoma‐type epidermal organs. The oldest known sipunculans were Golfingia‐like and had epidermal organs, which might resemble the architecture of the Golfingia‐type epidermal organs in extant taxa. Thus, it can be hypothesized that bimodal secretory cells (e.g. basophilic secretory cells) were part of the sipunculan ground pattern. Moreover, bimodal secretory cells of Phascolion look strikingly similar to those found in various annelid glands and thus might even be part of the ground pattern of stem species of Sipuncula + Pleistoannelida.     

Development of plant cuticles: fine structure and cutin composition of Clivia miniata Reg. leaves

The fine structure and monomeric composition of the ester-cutin fraction (susceptible to BF₃/CH₃OH transesterification) of the adaxial leaf cuticle of Clivia miniata Reg. were studied in relation to leaf and cuticle development. Clivia leaves grow at their base such that cuticle and tissues increase in age from the base to the tip. The zone of maximum growth (cell expansion) was located between 1 and 4 cm from the base. During cell expansion, the projected surface area of the upper epidermal cells increased by a factor of nine. In the growth region the cuticle consists mainly of a polylamellate cuticle proper of 100–250 nm thickness. After cell expansion has ceased both the outer epidermal wall and the cuticle increase in thickness. Thickening of the cuticle is accomplished by interposition of a cuticular layer between the cuticle proper and the cell wall. The cuticular layer exhibits a reticulate fine structure and contributes most of the total mass of the cuticle at positions above 6 cm from the leaf base. The composition of ester cutin changed with the age of cuticles. In depolymerisates from young cuticles, 26 different monomers could be detected whereas in older ones their number decreased to 13. At all developmental stages, 9,16-/10,16-dihydroxyhexadecanoic acid (positional isomers not separated), 18-hydroxy-9-octadecenoic acid, 9,10,18-trihydroxyoctadecanoic acid and 9,10-epoxy-18-hydroxyoctadecanoic acid were most frequent with the epoxy alkanoic acid clearly predominating (47% at 16 cm). The results are discussed as to (i) the age dependence of cutin composition, (ii) the relationship between fine structure and composition, (iii) the composition of the cuticle proper, the cuticular layer and the non-depolymerizable cutin fraction, and (iv) the polymeric structure of cutin.Abbreviations CL cuticular layer - CP cuticle proper - MX cutin polymer matrix     

The pheromonal gland of Lymantria dispar: Morphology and evidence for its innervation

The morphological features of the glandular epithelium that secretes pheromone in the polyphagous pest gypsy moth Lymantria dispar are described by light and electron microscopy. The monolayered gland cells are covered by the folded cuticle of the intersegmental membrane between the 8th and 9th abdominal segments showing neither sites of discontinuity nor distinct openings on its external surface. The cells bear a large, often irregularly shaped nucleus, and contain granules of variable amount and electron‐density. These granules are mostly located in the basal compartment of the cytoplasm, in a labyrinthine zone laying on a basement membrane. The apical membrane of the gland cells bear microvilli and cell–cell contact is established by different junctional structures. Nerve fibers enwrapped in glia are found beneath the basement membrane, in close contact with the secretory cells. This latter finding represents the first evidence of the innervation of the pheromonal gland in L. dispar. J. Morphol. 2009. © 2008 Wiley‐Liss, Inc.     

Ultrastructural investigations of presumed photoreceptors as a means of discrimination and identification of closely related species of the genus Microphthalmus (Polychaeta,Hesionidae)

Summary Differences in the ultrastructure of presumed photoreceptors of three morphologically similar Microphthalmus populations on the opposite sides of the Atlantic (German North Sea coast and coasts of North Carolina and Massachusetts) suggest the existence of three different species. Only the European M. listensis possesses three pairs of prostomial eyes, of which one pair has rhabdomeric receptors and pigment cells. The two other pairs are unpigmented and can be found in all three species. The frontal one has ciliary receptors, the posterior one rhabdomeric sensory cells. An additional unpaired potential photoreceptor organ in the segment with the first pair of tentacular cirri is present in all individuals of this species complex. It has a relatively high number of cilia with numerous microvillar projections. — For each type of ocellus there are slight but distinct and constant differences among the species such as relative position of sensory cells, presence of dilations of the ciliary shafts, number of cilia, and shape of the sensory cells. Presence of both ciliary and rhabdomeric light-sensitive cells is discussed with reference to various theories of the evolution of photoreceptors.Abbreviations ax axonema - bb basal body - cc cup cell - ci cilium - cu cuticle - epc epidermal cell - g Golgi apparatus - gp glycogen particles - mi mitochondrion - mv microvilli - mvb multivesicular body - nu nucleus - pc pigment cell - pg pigment granule - rer rough ER - smc submicrovillar cysternae - sr striated rootlet     

The ultrastructure of the marine gastrotrichTurbanella cornuta Remane (Macrodasyoidea) and its functional and phylogenetical importance

Summary The organization of marine gastrotrichs (Macrodasyoidea) is reviewed by ultrastructural analysis of one representative,Turbanella cornuta Remane, and the fine structure of tissues and cells is described. Turbanella cornuta has a mono-layeredcellular epidermis rich withsensory hairs, epidermal bodies, isolatedepidermal glands, glandular adhesive organs belonging to a duo-gland type, andventral ciliated epidermal cells of the multiciliated type. The voluminous neuropil of thebrain consists of a circular commissure which sends out four anterior and posterior longitudinal headnerves. The posterior ones unite on each side to one single longitudinal nerve of the periphery which is occupied with single peripheral neurons and has thin commissures that make it anorthogon. The position and the structure of the neurons indicate their sensitive, associative, motoric, and neurosecretory functions. The different forms of synapses give first hints to neuronal connections within gastrotrichs. There is a big cellularglia around the brain commissure and a small cellular glia within the brain neurons. In between the cross-striated muscle fibrils of thepharyngeal wall there are also nerves and sensory hairs.TheY-organ lies in the interior of the lateral body cavities, which are delimited by an outer musculature of the body wall and an inner musculature of the intestinal tract. In the pharyngeal region, theY-organ fills the body cavities completely and, in the intestinal region, it covers thegonads, which also lie in the lateral body cavities, dorsally. The testicles lie separately in front of the paired ovaries. Single states of oogenesis could be identified as oogonia, and young and old oocytes. There is a paired gland organ in front of the dorsomedian ovary which may produce a mucous cover for the egg.Theintestinal tract is adapted to mechanical stress by a myoepithelium in the pharyngeal region, by various interdigitations, and by narrow intercellular gaps with hemidesmosomal adhesions to the basement membrane. The majority of the resorbing intestinal cells have a high seam of microvilli and contain various numbers of lysosomes. In addition, there are some secerning cells without microvilli, but with a centrically arranged ER and with big secretion granules in the dorsomedian sector.The ultrastructure affirms a close correlation between the conditions of life in the interstitium and structural adaptations, such as may be observed in single structures of the body wall, the y-organ, the intestinal tract and, in some respect, even in the nervous system and in the formerly researched musculature and spermatohistogenesis. On the other hand, for the construction of the glandular adhesive organs, the nervous system, and the formerly investigated body cavities, a phylogenetical relevance is discussed. Thereafter, gastrotrichs have more primitive characters than the closely related nematodes.Abbreviations a sensory hair cells - am ampoule - at outleading tube - b basement membrane - bb basal body - c cilium - cr rootlet of the cilium - cu cuticle - cw cell wall - d d-cells of the brain - de desmosomes - e e-cells of the brain - eb epidermal bodies - ee ripe egg in the dorsomedian ovary - ep epidermis - er endoplasmatic reticulum - ev ventral ciliated epidermal cells - f f-cells of the brain - fr fibrillar structure - g gland cell - ge germ epithelium - gl₍₁₊₂₎ small and big cellular glia of the br - go Golgi-apparatus - gp genital pore - h h-cells of the brain - hf lateral adhesive tubules - hfp posterior adhesive tubules - i intestine - il intestinal lumen - 1 lumen of the organ - li lipid granules - ly lysosomes - m mitochondrium - mb multivesicular body - mc circular musculature - mi microvilli - ml longitudinal musculature - mo mouth opening - mt microtubules - mpl longitudinal muscle fibers of the pharyngeal wall - mpr radial muscle fibers of the pharyngeal wall - n nucleus - nb brain neurons - nc brain commissure - nf nerve fibers - nl lateral headnerve - nm nuclear membrane - nn nucleolus - nv ventrolateral headnerve - nz peripheric neuron - ncp peripheric nerve commissure - nvp longitudinal peripheric nerve - o lateral ovary - oc oocyte - oo oogonium - ow wall cells of the ovary - p secretory pore - ph pharynx - po palpar organ - phb pharyngeal bulbs - phl pharyngeal lumen - phn nerve plexus of the pharynx wall - sa anterior sense organ - sg secretory granules - sh sensory hair cell - sp posterior sense organ - st supporting stick - su supporting cell - sv synaptic vesicles - sy synaptic gap - t testicles - tl testicular lumen - tw wall cells of the testicles and the vas deferens - v ventral - va vacuoles - vd vas deferens - vs vesicles - y y-organ - yc anterior commissure of the y-organ - z yolk granules     

Ultrastructural study of two glandular systems in the proboscidial glandular epithelium of Riseriellus occultus (Nemertea, Heteronemertea)

 Two different types of glandular system in the proboscidial epithelium of Riseriellus occultus have been investigated by transmission electron microscopy. As expected, most of the epithelial cells are glandular in nature. With regard to differences in the ultrastructure of these gland cells and in the formation and morphology of their secretory granules, we have categorized and described four types of gland cell, indicated as G₁, G₂, G₃, and G₄. Each gland cell has a completely intraepithelial body characterized by a prominent nucleus, developed rough endoplasmic reticulum, Golgi complexes, and numerous secretory granules at different stages of maturation. These four types of gland cell appear associated in pairs forming numerous glandular systems of two types (A, B). These glandular systems are restricted to the ventral surface of the proboscis and are scattered irregularly throughout its length. Each glandular system consists of two gland cells of different types. The gland cell necks in each glandular system extend together to the epithelial surface; they protrude onto this and form a papilla where they open in a common area. The epithelial supportive cells adjacent to the glandular systems have long, stout microvilli which have a core of tonofilaments. These tonofilaments gather into dense bundles which pass vertically through the supportive cells and attach to the extracellular matrix underlaying the cells by hemidesmosomes. Moreover, a single sensory process stands close to each papilla. The ultrastructural morphology of the type A glandular systems suggests that they have an adhesive function operating in a similar way to that of the duo-gland adhesive systems in other invertebrate groups, although they are not homologous with these. The spatial arrangement of the secreted products of the type B glandular systems suggests that these may contribute to increasing the grip of the proboscis on the prey. The secretory granules (=pseudocnids) of the type G₃ gland cells are very likely an autapomorphy of the Anopla, providing a character by which the relationships within the Nemertea can be evaluated. Accepted: 9 October 1997     

The structure of the salt gland of Aegiceras corniculatum

Summary The salt glands of Aegiceras corniculatum have been examined by light- and electron-microscope techniques. A gland consists of a large number of abutting secretory cells and a single, large basal cell. The secretory cells and basal cell are joined by well defined plasmodesmata. The glandular cuticle shows differences between the top and sides of the gland, which may indicate a variation in the nature or quality of wax deposited. These variations may be significant in the secretion process, in view of the lack of evidence for the presence of pores. In ultrastructure, the secretory cells are generally similar to others that have been described, though there is no evidence of any particular association of vacuoles within these cells.