Comparative morphology of the foot structure of four genera of Loxosomatidae (Entoprocta): Implications for foot functions and taxonomy

Entoprocta is a group of mostly cryptic, benthic invertebrates with a sedentary lifestyle. Here, we investigate the morphology of the entoproct foot, which is an important structure in attachment and locomotion. We describe the foot structure of four solitary entoprocts, Loxosoma monilis, Loxosomella stomatophora, Loxocorone allax, and Loxomitra mizugamaensis, by means of light and transmission electron microscopy. Gland cells containing secretory granules were found in the foot of all the four species. In L. monilis, the gland cells densely paved the underside of the disc‐shaped foot, but no duct or groove was found. In L. stomatophora and L. allax, a foot gland was present at the frontal end of a foot groove. The foot gland was a solid cell mass in the former species but a sac‐like structure in the latter. Two types of groove accessory cells were recognized in both species; groove bulge cells (GBCs) showed large cytoplasmic bulges extending into the groove lumen, while groove microvillus cells have microvillus mats in the lateral wall of the groove. The bulges of GBCs in L. stomatophora are slender and attached to one another with desmosomes, forming appendages that extend down to the substratum, hinting at their contribution to attachment and locomotion. The bulges in L. allax form large swellings that fill the groove lumen and are connected to the surrounding cells with hemidesmosomes. In the liberated buds of L. mizugamaensis, tripartite gland cell masses were found at the basal end of the stalk, but no groove was found. A small invagination, which may be the opening of the gland, was found at the center of the foot tip, where the liberated buds attach themselves to the substratum and then metamorphose into adults. No openings were found at the lateral terminal wings, which support locomotion in Loxomitra species. J. Morphol. 271:1185–1196, 2010. © 2010 Wiley‐Liss, Inc.     

Byssus thread strength in the mussel, Mytilus edulis

Mytilus edulis attaches to the substratum by means of a proteinaceous byssus complex. This consists of three portions: a root, embedded in the pedal tissues, a stem, continuous with the root but external to the body and a number of byssus threads attached proximally to the stem and distally to the substratum via adhesive discs. Byssus strength varies seasonally on the shore, in response to changes in wave action (Price, in press). As a decline in byssal attachment strength implies a decline in strength of the constituent threads, a study was undertaken to establish the extent to which byssus thread strength is determined by age. The ultimate tensile stress, ultimate tensile strain and Young's Modulus were measured in threads of known age and length and a stepped regression performed on the results. It was found that age and length correlate significantly with tensile stress and Young's Modulus. Length is a less important influence than age on tensile stress but has a greater effect than age on Young's Modulus. Tensile strain is independent of both length and age.     

Byssus attachment strength of two mytilids in mono-specific and mixed-species mussel beds

The mussel Xenostrobus securis is endemic to the brackish waters of New Zealand and Australia, but has successfully invaded the inner Galician Rías of NW Spain, where it coexists with the indigenous mussel Mytilus galloprovincialis. In this laboratory study, the plasticity of the byssus attachment strength of two mytilids was compared by manipulating substratum, salinity, and bed assembly. M. galloprovincialis showed stronger byssus detachment strength than X. securis, despite lower byssus coverage. Both species responded similarly to the substratum, with substantially lower byssus strength on methacrylate, which offered the lowest surface free energy. Byssus detachment values for M. galloprovincialis were lower at lower salinity. In mixed beds, a number of mussels moved upwards, eventually colonising the upper layers of the assemblage. This behaviour increased byssus strength but only for X. securis. X. securis is adapted to a wide spectrum of abiotic conditions, a trait that may promote its dissemination within estuarine environments.     

盐度对企鹅珍珠贝足丝分泌的影响

企鹅珍珠贝（Pteria penguin）是生产附壳珍珠的大型海水经济贝类,其依靠强壮的足丝将自身固定在硬质基底上,抵抗水流的冲击和抵御被捕食等。足丝分泌和足丝的形状很容易受到环境的影响,本实验采用盐度30为低盐度组、盐度35为中盐度组和盐度40为高盐度组,研究这3种盐度对企鹅珍珠贝足丝分泌、足丝直径和足丝拉力的影响,通过单因素方差分析法（LSD法）分析这三个足丝相关指标在3种盐度组间是否存在显著性差异。结果显示,3种盐度下企鹅珍珠贝足丝附着率无显著差异,但在整个实验周期72 h内,中盐度组的足丝分泌总数为（48.7 ± 15.1）根,显著高于低盐度组的（24.7 ± 5.0）根和高盐度组的（13.3 ± 1.5）根。在实验的前6 h内,中盐度组的足丝首次附着率显著高于低盐度组和高盐度组（P < 0.05）,但在后续的12 h、18 h、30 h、42 h、54 h和66 h这6个时间点,3个盐度组的足丝首次附着率均无显著性差异。足丝直径未受盐度变化的影响,但盐度对足丝拉力具有显著影响,中盐度组的足丝拉力显著高于低盐度组和高盐度组（P < 0.05）。上述结果表明,企鹅珍珠贝为适应一定范围内盐度的改变,会在短时间内通过抑制足丝分泌来减少能量消耗,随着对环境的适应足丝分泌会恢复。盐度影响足丝分泌且对足丝拉力影响显著,但对足丝直径无明显影响。本研究可以为企鹅珍珠贝养殖及珍珠插核培育提供理论基础。     

Specialized cilia of the byssus attachment plaque forming region in Mytilus californianus

The distal depression of the ventral pedal groove of Mytilus californianus was investigated by scanning and transmission electron microscopy. This part of the byssus forming system is responsible for the formation of the attachment plaque of the byssus thread. The longitudinal pedal ducts open into this area and the floor of the distal depression is covered by specialized cilia which terminate as biconcave flattened discs or “paddles.” The disc is formed by a 360° curvature of the axoneme tip within the ciliary membrane. The diameter of the disc is about 1.33 μ while that of the shaft portion is 0.24 μ. There are about 11 cilia per square micron of surface area and the necks of the cilia are separated from each other by a web-like extension of apical cytoplasm extending from the epithelial cells. It is proposed that these specialized cilia function as microscopic spatulas for the application of the adhesive plaque material to substrate surfaces. The pattern of surface convection currents seen in vivo tends to support this hypothesis.     

利用蛋白质组学手段鉴定新型贻贝足丝蛋白

贻贝通过足腺分泌特有的足丝并以此粘附于水下各种基质表面.贻贝足丝中富含各种粘附蛋白,其优异的水下粘附性能使其成为开发新型生物粘合剂的候选分子.厚壳贻贝足丝粘附能力强,本文采用尿素及盐酸胍抽提结合二维双向电泳技术（two-dimensional electrophoresis, 2-DE）,分别对厚壳贻贝足丝纤维和足丝盘的蛋白质进行分离及染色;采用串联质谱技术结合常规搜库和表达序列标签（EST) 数据库搜索,对分离获得的蛋白质点进行鉴定,从中获得了mfp-3、mfp-6、胶原蛋白以及3种未曾报道过的新型贻贝足丝蛋白成分.上述研究为深入了解厚壳贻贝足丝蛋白的分子多样性、探讨其粘附机理以及从中筛选具有应用前景的贻贝足丝蛋白奠定了基础.     

The mucus producing glands and the distribution of the cilia of the pulmonate slug Limax pseudoflavus

The gross anatomy and histochemistry of the mucus-producing glands of Limax pseudoflavus Evans were investigated. The body mucus can be divided into three areas. The dorsal body surface is covered with a sulphated acid mucopolysaccharide/protein mixture secreted largely by five cell types. The pedal mucus is a mixture of neutral mucopolysaccharide from the suprapedal gland. The dorsal and pedal mucus sheets are separated by the peripodal groove whose cells secrete a weakly acid mucus. The duct of the suprapedal gland, the epidermis around the pneumostome, the ventral surface of the peripodal groove and the centre of the underside of the foot are ciliated. The dorsal and pedal mucus remain stationary relative to the body and the substrate respectively and the only rejection currents seen in the mucus are around the pneumostome.
It is suggested that the pedal mucus is formed by the mixture of the products of the suprapedal gland and the mucoprotein secreting gland in the leading edge of the foot, thus producing a mucus suitable for locomotion. Many areas of the animal (e.g. the head, pneumostome, sole and the leading edge of the foot) are capable of producing both a fluid (neutral or weakly acid) and a viscous (acid) mucus. It is postulated that such an arrangement allows for both adhesion and lubrication at different times.     

Functional anatomy of male copulatory organs of Pomacea canaliculata (Caenogastropoda, Ampullariidae)

This study was aimed to investigate the functional morphology of copulation and sperm transfer in the invasive snail Pomacea canaliculata. Three-dimensional renderings of the male copulatory apparatus were made and showed elaborate systems for innervation and for hemolymph supply and drainage. A key component of the male copulatory apparatus is the penial sheath, which shows three specialized glands; the medial and distal glands may participate in adherence to the mantle cavity wall of the female during copulation. The outer gland has an epithelium composed of columnar cells with branched microvilli, mucous goblet cells and large granular secretory cells containing intragranular crystalloids, which produce an exocrine secretion during copulation. The interaction of male/female copulatory organs was studied in dissections of snap-frozen pairs. Sperm are left in the sperm pit, at the end of the pallial spermiduct. Afterwards, the muscular action of the penial bulb takes the sperm up to the vermiform penis, which slides from the penial pouch into the central groove of the penial sheath, and it later emerges through a T-shaped sulcus of this structure and enters the female vagina. Then, it climbs through the capsule duct, and its tip reaches the proximity of the seminal receptacle. A model of copulation and sperm transfer is presented on the basis of the new findings and on published literature.     

Location and analysis of byssal structural proteins of Mytilus edulis

The acellular attachment organ (byssus) of the marine mussel Mytilus edulis L. is composed of threads that emanate from the body of the mussel to adhesive discs that anchor the threads to rocks, sand and other mussels. Three proteins have been purified by immunohistological methods and located to specific regions of the byssus. A collagenous protein with subunit molecular weights of 53,000, 55,000 and 65,000 is found in the matrix of the elastic thread region. Its 73,000-MW precursor was extracted from foot glands in the area proximal to the animal body and was identified by immune cross-reactivity. A cystine-rich, acidic protein was found in all regions of the byssus associated with a third protein, the polyphenolic protein. The L-dopa-containing polyphenolic protein appears in the cortex of the entire thread and adhesive plaque and at the substrate-plaque interface. Antiserum to this protein stains spherical vesicles in the phenol gland of the foot. Using immuno-electrophoretic methods, the polyphenolic protein and the cystine-rich protein were shown to form high molecular weight aggregates with aging of the byssus.     

Composition, secretion, and fate of the glands in the miracidium and sporocyst of Fasciola hepatica L

The anterior end of the miracidium of Fasciola hepatica contains a large flask-shaped apical gland and four unicellular lateral glands, all of which have ducts which pass to the tip of the apical papilla. These glands appear to be involved in penetration of the larva into the snail host. The apical gland secretes as the miracidium proves the epidermis of the host before attachment. It seems likely that its secretion is a chemical which lyses the epidermal cells. The lateral glands are PAS-positive and may contain a neutral mucopolysaccharide. They also secrete as the miracidium probes the snail and a layer of PAS-positive material may be seen at the leading edge of the apical papilla as the larva penetrates into the host. Both the apical gland and the lateral glands may be visible in the sporocyst for several days after penetration.     

Byssus production rate of the White Sea blue mussel <Emphasis Type="Italic">Mytilus edulis</Emphasis> (Linnaeus, 1758) in the presence of metabolites of some hydrobionts

The byssus production of the blue mussel Mytilus edulis L. was studied in the laboratory in the presence of the metabolites of the following animals: a predator (a starfish Asterias rubens L.) and several species competing with the mussel in White Sea fouling communities (a bivalve Hiatella arctica L. and a solitary ascidian Styela rustica L.). The byssus threads and attachment plaques produced by each mussel per day were counted. The number of byssus threads and plaques was smallest in pure sea water and in the presence of metabolites produced by conspecific individuals.     

Foot glands in Perna indica and Perna viridis (Pelecypoda: mytilidae) histology and histochemistry

The foot of Perna viridis is found to contain three main types of glands, the white gland, phenol gland and the enzyme gland. But in Perna indica there are only two glands, the phenol gland and the enzyme gland. Besides these, mucous glands are found in both of the species. The shape and size of the cells of these glands vary from species to species. Glycogen and 1 : 2 glycol groups are found in these gland cells. Proteins rich in disulfides and sulfhydryls are present in the phenol glands of both the species and in the white gland of p. viridis but they vary in the intensity of staining. The presence of phenols is confirmed in the phenol gland cells. Phospholipids and lipoproteins are intense in the white and phenol gland cells. They are absent in the enzyme gland. Alkaline and acid phosphatases activity in the enzyme gland cells could be demonstrated. The secretions of these glands help in the formation of the byssus threads. The mucous gland cells are subepithelial localised they secrete acid and neutral mucopolysaccharides together with glycoproteins. Which participate in the attachment of the byssus disc.     

Histological and histochemical observations on the foot glands in some byssus-bearing bivalves of the Waltair coast

Summary The glands responsible for the formation of the byssus threads inArca symmetrica, Barbatia obliquata andSeptifer bilocularis are the white gland, phenol gland and enzyme gland. Besides these, mucous glands are also present in the sub-epithelia. The size and shape of the cells of these glands vary in one and the same species. From histochemical investigations it has been revealed that these glands contain 1,2-glycol groups in addition to disulphides and sulphhydryls. The white gland secretes a protein material and the phenol gland is rich in phenols. These two combine to form a phenolic protein which is acted upon by a polyphenol oxidase secreted by the enzyme gland and leads to the formation of a byssus thread. The mucous gland cells secrete acid mucopolysaccharides, neutral mucins and glycoproteins.     

The pelvic kidney of male Ambystoma maculatum (Amphibia,urodela, ambystomatidae) with special reference to the sexual collecting ducts

This study details the gross and microscopic anatomy of the pelvic kidney in male Ambystoma maculatum. The nephron of male Ambystoma maculatum is divided into six distinct regions leading sequentially away from a renal corpuscle: (1) neck segment, which communicates with the coelomic cavity via a ventrally positioned pleuroperitoneal funnel, (2) proximal tubule, (3) intermediate segment, (4) distal tubule, (5) collecting tubule, and (6) collecting duct. The proximal tubule is divided into a vacuolated proximal region and a distal lysosomic region. The basal plasma membrane is modified into intertwining microvillus lamellae. The epithelium of the distal tubule varies little along its length and is demarcated by columns of mitochondria with their long axes oriented perpendicular to the basal lamina. The distal tubule possesses highly interdigitating microvillus lamellae from the lateral membranes and pronounced foot processes of the basal membrane that are not intertwined, but perpendicular to the basal lamina. The collecting tubule is lined by an epithelium with dark and light cells. Light cells are similar to those observed in the distal tuble except with less mitochondria and microvillus lamellae of the lateral and basal plasma membrane. Dark cells possess dark euchromatic nuclei and are filled with numerous small mitochondria. The epithelium of the neck segment, pleuroperitoneal funnel, and intermediate segment is composed entirely of ciliated cells with cilia protruding from only the central portion of the apical plasma membrane. The collecting duct is lined by a highly secretory epithelium that produces numerous membrane bound granules that stain positively for neutral carbohydrates and proteins. Apically positioned ciliated cells are intercalated between secretory cells. The collecting ducts anastomose caudally and unite with the Wolffian duct via a common collecting duct. The Wolffian duct is secretory, but not to the extent of the collecting duct, synthesizes neutral carbohydrates and proteins, and is also lined by apical ciliated cells intercalated between secretory cells. Although functional aspects associated with the morphological variation along the length of the proximal portions of the nephron have been investigated, the role of a highly secretory collecting duct has not. Historical data that implicated secretory activity concordant with mating activity, and similarity of structure and chemistry to sexual segments of the kidneys in other vertebrates, lead us to believe that the collecting duct functions as a secondary sexual organ in Ambystoma maculatum. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

Histology and regeneration of the radula of Pomacea bridgesi (Gastropoda,Prosobranchia)

Summary Histology, physiological regeneration, and degradation of the taenioglossan prosobranch radula and its concomitant epithelia were studied by light and electron microscopy (TEM, SEM), electron microprobe analysis, and autoradiography. Taenioglossa have seven multicellular odontoblastic cushions which produce the tooth matrix by apocrine secretion; many long microvilli are also incorporated. In contrast to pulmonates, the odontoblasts of prosobranchs are capable of division, and their mitoses contribute to the expansion of the cushions, but presumably also to the displacement of degenerating odontoblasts. The seven cushions are isolated from each other by separation cells. The radular membrane is produced from microvilli of membranoblasts and a substance secreted at the base of microvilli.Strands of the supraradular epithelium subsequently move in between the teeth and finally enclose them completely. They effect the hardening and mineralization of the teeth. The strands move together with the radula towards the anterior and are extruded at the opening of the radular sheath; their degeneration, however, has already started in the middle section of the sheath. Epithelial cells are produced by two completely separated mitotic centres which lie dorsolaterally at the end of the sheath.In the subradular epithelium, mitotic activity is scattered over the posterior half of the sheath but is not found in the region where the supramedian radula tensor muscle is inserted. The epithelial cells move forward, but at a much lower rate than the radula. At the opening of the sheath the subradular membrane is generated, while cells of the subradular epithelium lying between the lamellae of the subradular membrane are extruded.The subradular membrane is limited to the functional part of the radula. It is situated on the distal radular epithelium, which is obviously not a continuation of the subradular epithelium. In test animals treated with tritiated thymidine, there is a very strong stationary centre of labeled cells at the beginning of the epithelium, but so far no mitoses have been found in this centre and the labeled cells do not move on continually. In the middle of the distal epithelium mitoses do occur, and the labeled cells permit the assumption that these cells do not migrate at all to the anterior end. At least in Prosobranchia, the distal radular epithelium does not transport the radula to its degradation zone. The transport mechanism for the radula is still unknown.     

Organization of unusual idiosomal glands in a water mite, <Emphasis Type="Italic">Teutonia cometes</Emphasis> (Teutoniidae)

The unusual idiosomal glands of a water mite Teutonia cometes (Koch 1837) were examined by means of transmission and scanning electron microscopy as well as on semi-thin sections. One pair of these glands is situated ventrally in the body cavity of the idiosoma. They run posteriorly from the terminal opening (distal end) on epimeres IV and gradually dilate to their proximal blind end. The terminal opening of each gland is armed with the two fine hair-like mechanoreceptive sensilla (‘pre-anal external’ setae). The proximal part of the glands is formed of columnar secretory epithelium with a voluminous central lumen containing a large single ‘globule’ of electron-dense secretory material. The secretory gland cells contain large nuclei and intensively developed rough endoplasmic reticulum. Secretory granules of Golgi origin are scattered throughout the cell volume in small groups and are discharged from the cells into the lumen between the scarce apical microvilli. The distal part of the glands is formed of another cell type that is not secretory. These cells are composed of narrow strips of the cytoplasm leaving the large intracellular vacuoles. A short excretory cuticular duct formed by special excretory duct cells connects the glands with the external medium. At the base of the terminal opening a cuticular funnel strengthens the gland termination. At the apex of this funnel a valve prevents back-flow of the extruded secretion. These glands, as other dermal glands of water mites, are thought to play a protective role and react to external stimuli with the help of the hair-like sensilla.     

Histochemical and ultrastructural study on the innervation of the byssus glands of Mytilus galloprovincialis

The aluminium-formaldehyde (ALFA) histofluorescence method reveals an extensive plexus of brilliant greenish monoaminergic elements in the glandular zones of the Mytilus foot, while only scanty nerve fibres are acetylcholinesterase-positive. By electron microscopy, bundles of nerve fibres can be seen i) in close connection with the intrinsic musculature located in the connective septa among the glands, and ii) near the cell bodies and necks of all the byssus glands. The nerve fibres show varicosities containing three types of vesicles: small clear (50-60 nm), small granular (80-90 nm), and large granular (160-200 nm). The regions of close apposition between nerve terminals and muscle or gland cells generally do not show typical pre- or postsynaptic specializations. Along the pedal groove, mainly in the proximal two thirds of the foot, peripheral bipolar neurons can be detected, both by fluorescence and electron microscopy.     

Byssus production ability and degree of byssal-gland development in the infaunal clam Ruditapes philippinarum

Byssus production of Ruditapes philippinarum clams becomes reduced with growth. This tendency is well recognized but has not been analysed in detail. Additionally, it remains uninvestigated whether the lack of competence to produce byssus threads in the adult stage is caused by atrophy of the byssal glands or not. The objective of this study was to evaluate the byssus production ability of clams through the juvenile to adult stages and to examine the importance of two endogenous factors (i.e. shell size, somatic condition) in determining the byssus production probability (proportion of clams with byssus production in a population). This study also histologically confirmed the presence of byssal glands in juvenile to adult clams. For these purposes, field surveys to investigate the relationship among byssus production, shell size and somatic condition of clams collected from four intertidal sites and a histological study for byssal glands of the clams was conducted. This study revealed that byssus production probability decreases with increasing shell size and declining somatic condition and that the lack of byssus production is not caused by the loss of the byssal glands.     

Role of the midgut gland in purine excretion in the robber crab,Birgus latro (Anomura: Coenobitidae)

White fecal strands of Birgus latro are composed of small spherules of uric acid with a mean diameter of 1.6 ± 0.6 μm. Large numbers of membrane‐bound spherules with concentric lamellae are present in the R cells of the midgut gland, so we suggest that lengths of white feces are produced by coordinated secretion of these spherules into the lumen of the midgut gland tubules. There are four cell types in the tubules with embryonic (E) cells at the distal tip, B cells in a narrow band at the distal end and R cells making up the bulk of the tubules and gland. F cells are sparsely scattered among the R cells. Midgut gland tissue was assayed for activities of xanthine dehydrogenase and xanthine oxidase, the two forms of xanthine oxidoreductase. Contrary to previous reports, we found that the midgut gland of B. latro contains only high activities of xanthine dehydrogenase. If proteinase inhibitors were omitted from the assays, however, significant activity of xanthine oxidase was measured, a result we regard as an artifact attributable to the partial conversion of xanthine dehydrogenase to xanthine oxidase by endogenous proteinases. R cells were demonstrated to contain peroxisomes, which may be involved in lipid metabolism rather than synthesis of uric acid. J. Morphol. 241:227–235, 1999 © 1999 Wiley‐Liss, Inc.