淡水贝类贝壳多层构造形成研究

对几种淡水贝（包括蚌、螺）进行形态及组织学观察，并通过实验方法重现贝壳三种物质，即：角质、棱柱质、珍珠质的生成过程，结果表明：外套膜外表皮细胞是由相同类型细胞组成，这些相同细胞在不同的作用条件下形成贝壳多层构造。     

Interaction of photoperiod and nutritive state in female reproduction of Lymnaea stagnalis

Summary

A study was made of the interaction of the photoperiod and the availability of food in influencing egg laying of the freshwater snail Lymnaea stagnalis. At a long day photoperiod (LD = 16 h light/8 h dark) egg laying of fed snails had increased compared with that of fed animals kept at a medium day photoperiod (MD = 12 h light/12 h dark). In MD snails oviposition ceased within a week of the beginning of a starvation period. This is most probably due to a reduction in the activities of the neuroendocrine caudodorsal cells which secrete an ovulation hormone. In contrast, in starved LD snails a low rate of ovipository activity continued, indicating that a lowered frequency of caudodorsal cell release cycles occurred under these conditions. The decreased mean size (number of eggs) of the egg masses in starved LD snails indicates that the activities of the endocrine dorsal bodies, which control vitellogenesis and synthetic activities in the female accessory sex organs, had decreased.

All MD snails survived, but nearly all LD snails died during the course of the experiment. Determinations of the mantle glycogen stores of LD snails suggest that the high mortality of LD snails is due to exhaustion of the animal's energy reserves.     

THE YELLOW PIGMENT CELLS OF HYDROBIA ULVAE (PENNANT) (MOLLUSCA : PROSOBRANCHIA)

The distribution of yellow pigment cells in the veliger larvaeand post-metamorphic snails of Hydrobia ulvae has been recorded.The number of cells increases with the size of the snail andthe pigment is characteristic of the foot of the veliger larva,and the foot, mantle, tentacles and penis of adult snails. Thecells contain numerous, double membrane-bound vesicles and havea highly granular cytoplasm. The absorption spectra of acetoneand methanolic HC1 extracts show single peaks at 337 and 392nm respectively, while chloroform extracts show peaks at 249,274 and 283 nm with an inflexion at 293 nm. The pigment hasa pale green fluorescence in ultraviolet light. The resultsof feeding and starvation experiments using larval and post-metamorphicsnails lead to the hypothesis that the pigment is a waste productof metabolism which is stored in the vesicles of the cells (Received 3 January 1979;     

An ultrastructural study of the mantle of the barnacle, Elminius modestus Darwin in relation to shell formation

The fine structure of the mantle and shell of the barnacle, Elminius modestus Darwin has been examined by electron microscopy. The epithelial cells along the outer face of the mantle differ in size, shape, and organelle complexity according to the different components of the shell they secrete. The shell consists of a non-calcareous basis and calcareous mural and opercular plates which are connected by a flexible opercular hinge. Both the basis and opercular hinge are composed of two main units: an outer cuticulin layer and a lamellate component of well ordered arched fibrils. During the deposition of the latter structures morphological changes in the cells occur which may be correlated with the moulting cycle. Preliminary results show that the calcareous plates are covered by an outer epicuticle, which is bordered by a cuticulin layer; the inner calcareous component, consists of an orderly arrangement of organic matrix envelopes within which crystals may be initiated.

The cells lining the inner surface of the mantle are uniform in appearance with a thin cuticle at their free surface which lines the body cavity. The latter structure of the cuticle and manner of its deposition are similar to those of the basis and opercular hinge. Separating the outer and inner mantle epithelial cells is connective tissue which comprises several differing cell types. The possibilities are discussed of the rôle these cells may play in shell deposition. The modes by which underlying cells secrete the different shell components and the cuticle lining the inner face of the mantle, are also discussed.     

The formation and turnover of the membranocalyx on the tegument of Schistosoma mansoni.

The multilaminate vesicles present in the tegument cytoplasm appear to fuse with side channels projecting out into the cytoplasm from the base of the surface pits. Their lamellate contents then unroll and spread out to form a trilaminate membranocalyx lining the pits and covering the tegument surface. The plant lectin concanavalin A appears to stabilize the process of vesicle fusion leading to an aggregation of multilaminate vesicles trapped in the lumen of the surface pits. The membranocalyx can be labelled with cationized ferritin. Chase incubations in normal medium indicate that by 4 h most of the label and the membranocalyx to which it is bound have been lost to the medium. This suggests that under the conditions of these experiments the membranocalyx has a half-life of 2-3 h.     

Embryonic development of the shell in biomphalaria glabrata (Say).

During embryogenesis of the fresh water snail Biomphalaria glabrata (Say) (Pulmonata, Basommatophora) shell formation has been studied by light and electron microscopical techniques. The shell field invagination (SFI), the secretion of the first shell layers, the development of the shell-forming mantle edge gland and spindle formation have been investigated. During embryonic development at 28 degrees C environmental temperature, the shell field invaginates after 35 h. After 40 h the SFI is closed apically by cellular protrusions and scale-like precursors of the periostracum. The first electron translucent layer of the periostracum stems from electron dense vesicles of the cells which lie at the opening of the SFI. A second electron dense layer appears some hours afterwards. When the shell appears birefringent in the polarizing microscope (45 h of development) calcium can be detected in it using energy dispersive x-ray analysis. As calcification occurs the intercrystalline matrix appears under the periostracum and the SFI begins to open. In embryos of 60 h the mantle cavity appears at the left caudal side. When the mantle edge groove develops (65 h of development) lamellate units are added to the outer layer of the periostracum, but no distinct lamellar layer is formed in B. glabrata. In addition to the lamellar cell and the periostracum cell, a secretory cell can be observed in the developing groove. After 65 h of development, spindle formation starts and the shell begins to coil in a left hand spiral. After 5 days of development the embryos are ready to leave the egg capsules.     

Resistance to desiccation and distribution patterns in bush-dwelling land snails

Bush-dwelling land snails are exposed to desiccating conditions that are more severe than those of snails that seek the shelter of rock crevices, litter or the upper layers of the soil. We studied the resistance to desiccation in four bush-dwelling species of Israeli snails to evaluate a possible relation between their water economy and their distribution pattern. The resistance to desiccation decreased in the following order: Xeropicta vestalis (a widely distributed Mediterranean species), Trochoidea simulata (a desert species), Theba pisana (a Mediterranean species from the sand dunes of the coastal plain), and Monacha haifaensis (a Mediterranean species). Xeropicta vestalis also had the quickest response to the desiccating conditions. It is probably prevented from establishing itself in the desert, in spite of its superior water economy, because it is an annual, semelparous species, and the desert is a highly unpredictable environment. An immediate response to desiccating conditions may be a key factor in the success of desert-inhabiting land snails. Snails from more humid regions take several days to recruit their water preserving mechanisms, a delay which may be crucial to their water balance. The conchiometrics of X. vestalis and T. simulata suggest that the main water preserving mechanisms of these species are located in the mantle, rather than in the shell and epiphragm.     

Effect of immersion at low tide on distribution and movement of the mud snail, Ilyanassa obsoleta (Say), in the upper Bay of Fundy, eastern Canada

Habitat heterogeneity often affects movement behaviours of animals, and consequently their spatial distribution. We evaluated the effect of immersion at low tide on the distribution, fine-scale movement patterns and daily movement patterns of the mud snail Ilyanassa obsoleta on a mudflat in the upper Bay of Fundy, Canada. Mud snails migrate onto intertidal mudflats in the summer, and our field survey showed that their density was higher inside tide pools relative to adjacent areas that are exposed at low tide. Using time-lapse videography, we evaluated the effect of snail size, snail density, and immersion at low tide on fine-scale movement patterns of I. obsoleta. Time until snails stopped moving and burrowed was unaffected by snail size, but snails at low and high densities burrowed somewhat faster than those at intermediate densities. Snail size and snail density had no detectable effect on displacement speed or linearity of displacement. Immersion affected snail movement: snails within tide pools delayed burrowing and traveled in more convoluted paths compared to those on exposed mud. Snails increased their turning angles within tide pools, which is probably the mechanism by which aggregations are formed. We also performed a mark-recapture experiment to compare daily movement patterns of snails released inside and outside tide pools. Snails released in tide pools moved shorter distances, but did not orient themselves differently than snails released outside tide pools. Both groups exhibited significant directionality, moving against the mean water current direction over 24 h. In sum, immersion at low tide affected the behaviour and spatial distribution of snails, resulting in snail aggregations within tide pools. These snail aggregations, in turn, may be a major factor influencing spatial dynamics on mudflats, including causing changes in distribution patterns of the burrowing amphipod Corophium volutator, a dominant inhabitant and key species in the food web of mudflats.     

Ultrastructure of chloride cells in young adults of the anadromous sea lamprey, Petromyzon marinus L., in fresh water and during adaptation to sea water.

The chloride cells in the interlamellar areas of the gills of young adult, anadromous sea lampreys, Petromyzon marinus L., captured in fresh water undergo structural modification during the adaptation of these animals to sea water. In fresh water the chloride cells are partially overlapped by mucus-secreting superficial cells and contain an extensive reticulum of cytoplasmic tubules, which are confluent with both lateral and basal plasma membranes, numerous mitochondria, a Golgi complex of moderate size, and numerous apical vesicles. Adaptation to sea water results in a retraction of the superficial cells, exposing the entire apical surface of the chloride cells, and a proliferation of both cytoplasmic tubules and mitochondria. Extensive enlargement of the Golgi complex in the chloride cells of these animals suggests the involvement of this organelle in the proliferation of cytoplasmic tubules. The extracellular tracer, ruthenium red, enters the tubules from the lateral or basal intercellular spaces in both freshwater- and seawater-adapted animals but never enters either tubules or vesicles from the apical surfaces, indicating that these are not confluent. The presence of dividing basal cells and newly-forming chloride cells, combined with evidence of degeneration of chloride cells, suggests that there is a turnover of this cell type. Both superficial and basal cells are phagocytic and involved in heterophagy of degenerating chloride cells. This phenomenon occurs in both fresh water and sea water indicating that the chloride cells may be functional in both environments.     

CHLOROPLAST DEVELOPMENT IN OCHROMONAS DANICA

When dark-grown cells of Ochromonas danica are placed in the light, the amount of chlorophyll a per cell increases 82-fold; the content of carotenoid pigment, 24-fold. Concomitantly with this increase in chlorophyll and carotenoid pigment, the small proplastid of dark-grown cells develops into a large lamellate chloroplast. During the first 12 hours in the light, vesicles appear within the loose clusters of dense chloroplast granules, enlarge, align themselves into rows (plates in three dimensions), and fuse into discs. Double discs may form from the more or less simultaneous fusion of two adjacent plates of vesicles or by the addition of vesicles to an already formed single disc. Three-disc bands arise by the addition of a disc to an already formed two-disc band through the approach and fusion of more vesicles. After 24 hours in the light, most of the chloroplast bands contain three discs, but the chloroplasts are still small. After 48 hours in the light, almost all the cells contain full-sized chloroplasts with a full complement of three-disc bands. However, at this time the amount of chlorophyll a and carotenoid pigment is only one-half of maximum. During the next 3 days in the light, as the number of chlorophyll and carotenoid molecules per chloroplast approximately doubles, there is a compression of the discs in each band (from 180 to 130 A) and a precise alignment of their membranes. Changes also occur in the nucleus when dark-grown cells are placed in the light. There is an increase in the number of small nucleolar bodies, many of which lie directly against the nuclear envelope, and in a few cells a dense mass of granules is seen between the two membranes of the nuclear envelope.     

Trichobilharzia ocellata: physiological characterization of giant growth, glycogen depletion, and absence of reproductive activity in the intermediate snail host, Lymnaea stagnalis

Giant growth, depletion of energy stores, and inhibition of reproductive activity are striking effects of many trematode parasites on their intermediate snail hosts. Two hypotheses have been put forward to explain these phenomena: (1) host and parasite compete for energy rich and other essential nutrients, with the parasite as the winner, and (2) the parasite intervenes in the endocrine control of reproduction of the snail. These hypotheses were tested in the present study with the Trichobilharzia ocellata/Lymnaea stagnalis association. The snails were infected at a juvenile stage, and release of cercariae started on Day 55 after exposure. It was shown that enhanced growth of infected snails is not paralleled by a greater increase in dry weight, but hemolymph volume does increase, being 35% greater than in the noninfected controls. Control snails, on the other hand, showed an increase in the percentage body dry weight during sexual maturation. The conclusion is that infected snails retain an essentially juvenile body structure. In control snails, glycogen was depleted from the mantle store at the start of egg laying but the onset of cercariae production marked a severe glycogen depletion from the headfoot and the mantle in infected snails, being nearly complete on Day 68 after exposure. The hemolymph glucose concentration was only slightly lower in infected than in control snails and it did not change (in both groups) during glycogen mobilization. This suggests that glycogen mobilization does not result from the snail and the parasite competing directly for metabolites within the hemolymph. Infection inhibited the maturation of the accessory sex organs: there was no increase in the relative wet weights nor in the amounts of DNA and secretion products in the albumin and prostate glands. Infected snails did not lay eggs. It is presumed that the parasite produces one or more agents which intervene in the action of the gonadotrophic hormones. The release of these agents commences at an early stage of infection.     

OBSERVATIONS ON THE STRUCTURE OF SOME FORMS OF GOMPHONEMA PARVULUM KÜTZ. III. FRUSTULE FORMATION1

Gomphonema parvulum Kütz. was investigated by electron microscopy for details of frustule formation. An expansion of the cell along the pervalvar plane occurs prior to cell division. After nuclear division the organelles are, separated into 2 entities, either by division or by dispersion. The cell divides into 2 halves by the invagination of the plasmalemma which is derived from Golgi vesicular activity. When cytoplasmic cleavage, is complete, the Golgi actively produces electronlucent vesicles which collect and coalesce beneath the. plasmalemma to form the silicalemma around the silicon deposition vesicle. The endoplasmic reticulum is also closely associated with this vesicular activity. The vesicle gradually expands and becomes extremely electron dense as silica is deposited within it—first in the region, followed by the mantle edge. When the valve is mature, Golgi vesicles collect and fuse to form the silicalemma of the first girdle band. The first girdle band becomes aligned against the mantle edge on completion, by the “sloughing off” of the external silicalemma and plasmalemma. The second and third bands are formed, individually in a similar manner. Separation of the 2 daughter cells commences at the apical pole and progresses to the basal pole. The plasmalemma and external silicalemma are “sloughed off” so that the 2 cells can separate. The inner segment of the silicalemma becomes the new plasmalemma of the daughter cell.     

Camouflaged or tanned: plasticity in freshwater snail pigmentation

By having phenotypically plastic traits, many organisms optimize their fitness in response to fluctuating threats. Freshwater snails with translucent shells, e.g. snails from the Radix genus, differ considerably in their mantle pigmentation patterns, with snails from the same water body ranging from being completely dark pigmented to having only a few dark patterns. These pigmentation differences have previously been suggested to be genetically fixed, but we propose that this polymorphism is owing to phenotypic plasticity in response to a fluctuating environment. Hence, we here aimed to assess whether common stressors, including ultraviolet radiation (UVR) and predation, induce a plastic response in mantle pigmentation patterns of Radix balthica. We show, in contrast to previous studies, that snails are plastic in their expression of mantle pigmentation in response to changes in UVR and predator threats, i.e. differences among populations are not genetically fixed. When exposed to cues from visually hunting fish, R. balthica increased the proportion of their dark pigmentation, suggesting a crypsis strategy. Snails increased their pigmentation even further in response to UVR, but this also led to a reduction in pattern complexity. Furthermore, when exposed to UVR and fish simultaneously, snails responded in the same way as in the UVR treatment, suggesting a trade-off between photoprotection and crypsis.     

Ultrastructure of type-I salivary-gland acini in four species of ticks and the influence of hydration states on the type-I acini ofAmblyomma americanum

We describe the ultrastructure of type-I salivary-gland acini in two argasid and two ixodid species. The basic cell types in the agranular or type-I acini, and their associations, are very similar in argasids and ixodids; therefore, we propose an anatomical nomenclature for cells in the type-I acinus based on the adult ixodidsAmblyomma americanum andDermacentor variabilis, and the argasid adultArgas (Persicargas) arboreus and on nymphalOrnithodoros moubata. Four cell types were present in all specimens: one central lamellate cell, a variable number of peripheral lamellate cells, a variable number of peritubular cells depending on the species, and one circumlumenal cell. The lamellate cells had infolded basal plasma membranes that presented an amplified surface area to the hemolymph. These cells most likely secreted the fluid involved in water vapor uptake by ticks. ForAmblyomma americanum females, abundant K⁺-dependent, ouabain-sensitive Na⁺, K⁺-ATPase complexes were located on the infolded basal plasma membranes of the lamellate cells. Apical membranes of the lamellate cells, and plasma membranes of other cell types in the acinus had little or no evidence of Na⁺, K⁺-ATPase activity. Only the central lamellate cell extended from the hemolymph of the acinus to its lumen; peripheral cells did not contact the lumen. Except when the ticks were rehydrating, lipid inclusions were common features in the lamellate cells of the ixodids. Lipid inclusions were not seen in argasid type I acini; however, glycogen deposits were common. To determine if acinar cells respond to the changing hydration state of the tick, unfed femaleA. americanum were subjected to dehydration/rehydrating conditions. During rehydration, mitochondria in the lamellate cells changed from a matrix of medium electron-density and intermembrane space (orthodox configuration) to a matrix of greater density and larger intermembrane space (condensed configuration). The orthodox configuration was consistently observed in control and dehydrating ticks. The condensed configuration was the norm for mitochondria in lamellate cells of rehydrating ticks. Lipid inclusions were depleted in the rehydrating ticks compared to control or dehydrating ticks. Acini appeared to be reverting to the control or desiccated state when ticks were returned to low humidity, suggesting that these changes were cyclical. Nymphs ofO. moubata subjected to the same dehydration/rehydrating conditions showed no obvious ultrastructural changes.     

Development of cytoplasmic digitations between Leydig cells and testicular macrophages of the rat

Summary Testicular macrophages and Leydig cells from adult animals are known to be functionally coupled. For example, secreted products from macrophages stimulate testosterone secretion by Leydig cells. In adult rat testes, structural coupling also exists between these cells. This coupling consists of cytoplasmic projections from Leydig cells located within cytoplasmic invaginations of macrophages. Although macrophages are known to exist in the testis in immature animals, it is not known when these digitations develop. The purpose of the present study was to determine whether the time of their development coincides with known maturational events that occur in Leydig cells, particularly during the peripubertal period. Testes from rats at 20, 30 and 40-days-of-age as well as testes from mature rats weighing more than 500 gm were prepared for ultrastructural analysis. It was found that digitations form between 20 and 30-days-of-age. These structures varied from simple tubular projections to complicated branched structures, suggesting that digitations are more than simple invaginations of microvilli into coated vesicles as previously described. Subplasmalemmal linear densities were also observed within macrophages juxtaposed to Leydig cells. Collagen was commonly observed between macrophages and Leydig cells in animals 20 days old. These studies demonstrate that although macrophages are present in the testis in maximal numbers at 20 days-of-age, they do not form junctions with Leydig cells until day 30. This is just prior to the major increase in secretory activity of rat Leydig cells that occurs during puberty.     

How stress alters memory in 'smart' snails

Cognitive ability varies within species, but whether this variation alters the manner in which memory formation is affected by environmental stress is unclear. The great pond snail, Lymnaea stagnalis, is commonly used as model species in studies of learning and memory. The majority of those studies used a single laboratory strain (i.e. the Dutch strain) originating from a wild population in the Netherlands. However, our recent work has identified natural populations that demonstrate significantly enhanced long-term memory (LTM) formation relative to the Dutch strain following operant conditioning of aerial respiratory behaviour. Here we assess how two populations with enhanced memory formation (i.e. 'smart' snails), one from Canada (Trans Canada 1: TC1) and one from the U.K. (Chilton Moor: CM) respond to ecologically relevant stressors. In control conditions the Dutch strain forms memory lasting 1-3 h following a single 0.5 h training session in our standard calcium pond water (80 mg/l [Ca(2+)]), whereas the TC1 and CM populations formed LTM lasting 5+ days following this training regime. Exposure to low environmental calcium pond water (20 mg/l [Ca(2+)]), which blocks LTM in the Dutch strain, reduced LTM retention to 24 h in the TC1 and CM populations. Crowding (20 snails in 100 ml) immediately prior to training blocks LTM in the Dutch strain, and also did so in TC1 and CM populations. Therefore, snails with enhanced cognitive ability respond to these ecologically relevant stressors in a similar manner to the Dutch strain, but are more robust at forming LTM in a low calcium environment. Despite the two populations (CM and TC1) originating from different continents, LTM formation was indistinguishable in both control and stressed conditions. This indicates that the underlying mechanisms controlling cognitive differences among populations may be highly conserved in L. stagnalis.     

The Structure and Development of the Apical Ganglion in the Sea Urchin Pluteus Larvae of Strongylocentrotus droebachiensis and Mespilia globulus

The structure of the apical ganglion is described using transmission electron microscopy and ultrastructural immunohistochemical localization with anti-serotonin, and the development of these nerve cells in animalized and vegetalized embryos, and embryos treated with Ca²⁺-deficient sea water are demonstrated with immunofluorescence microscopy. The axons within the neuropile contain clear and dense-core vesicles, but all the vesicles appear anti-serotonin immunoreactive. The principal type of neuron within the apical ganglions is anti-serotonin immunoreactive. In the animalized embryos, serotonergic neuroblasts and neurons appear in the second quarter of animal-vegetal axis. Serotonergic cells were not detected in vegetalized exogestrulae. Mespilia globulus embryos treated with Ca²⁺-deficient sea water ruptured to form a cellular sheet on the substratum. In ruptured embryos serotonergic neurons formed a ring around the area corresponding to the apical plate of normal embryos. These findings indicated that the serotonergic preoral nerve cells of echinopluteus derive from cells on the periphery of the apical plate.     

The effects of aestivation on the catalytic and regulatory properties of pyruvate kinase from Helix aspersa.

1. Pyruvate kinase was partially purified from the foot, mantle, and digestive gland of active and aestivating snails. 2. At pH 7.0 the apparent Km values for phosphoenolpyruvate (PEP) were 0.064 mmol/l for the enzyme from foot and 0.071 mmol/l for the enzyme from mantle; those for ADP were 0.35 mmol/l for the foot enzyme and 0.33 mmol/l for the mantle enzyme. 3. Both enzymes were inhibited by alanine, and this could be reversed by fructose 1,6-bisphosphate (FBP), although FBP alone was a weak activator. 4. Decreasing the pH to 6.5 markedly increased the inhibition by alanine and reduced the response to FBP. 5. The enzymes from these tissues of aestivating snails showed a small decrease in their affinity for PEP and a small increase in the effectiveness of alanine as an inhibitor. 6. These changes are indicative of a down-regulation of this enzyme which is consistent with the observations in other species during metabolic depression. 7. In contrast the enzyme from the digestive gland of active animals showed sigmoidal saturation kinetics for PEP with a S0.5 of 1.2 mmol/l, but had a markedly higher affinity for PEP, S0.5 = 0.20 mmol/l during aestivation. This may be indicative of other metabolic changes occurring in the digestive gland.     

Extracellular Matrix Penetration by Epithelial Cells Is Influenced by Quantitative Changes in Basement Membrane Components and Growth Factors

We have previously shown that isolated mouse fetal choroid plexus epithelial (CPE) cells penetrate a basement membrane matrix (Matrigel) substratein vitroto form single-layered epithelial vesicles embedded within the matrix. To determine which properties of the matrix are important for inducing or permitting cells to penetrate the substrate and organize into multicellular vesicles we have made quantitative changes to the basement membrane components and growth factors in cell cultures. Matrigel diluted to 33 or 10% with a collagen I gel was not permissive to cell invasion, and CPE cells formed a polarized epithelial monolayer on the substrate surface which had ultrastructural characteristics similar to those of CPE vesicles. Cells in these monolayers proliferated more rapidly than cells in epithelial vesicles. When deliberately embedded within a 33 or 10% Matrigel matrix, CPE cells were able to form vesicles, indicating that a dilute matrix is nonpermissive to cell invasion but promotes epithelial polarization and organization into vesicles. Cells embedded within a 100% collagen I matrix did not proliferate or form epithelial vesicles and the majority of cells did not remain viable. Addition of laminin to the collagen I gel promoted cell adhesion and cell survival, but did not promote the formation of extensive monolayers on the substrate nor the formation of epithelial vesicles within the matrix. Cell invasion into the 33% Matrigel matrix was induced by addition of laminin, nidogen, or a laminin–nidogen complex to the substrate or by addition of TGFβ2 to the culture medium, but not TGFβ1 or PDGF. These studies show that CPE cells are sensitive to quantitative changes in matrix composition, which influences their survival and proliferation and also their ability to penetrate the matrix and organize into multicellular epithelial vesicles.     

Respiration in air and water of three mangrove snails

The oxygen consumption of three species of Malaysian mangrove gastropods was measured in air and sea water at the temperatures commonly recorded in the mangrove. The experiments in air were carried out after the animals had regained fluid lost from the mantle due to handling. Fluid loss can have considerable effects on rate of oxygen consumption. Nerita arliculata (Gould) was found throughout the mangrove and experiences from 50 to 92% aerial exposure. It has a gill and a ratio of aerial to aquatic respiration rates of 2.7 at 28°C. 50% of the animals can survive underwater for 72 h at 28°C. The other two species, Cerithidea obtusa (Lamarck) and Cassidula aurisfelis (Brugière) experience over 95% aerial exposure, have their mantle cavities modified as lungs and have air : water respiration rate ratios of 5.5 and 6.0, respectively. 50% can survive from 48 to 36 h underwater at 28°C. Acclimated animals have Q₁₀'s of about 1.6 in air and 1.4 in water. The respiratory physiology of the snails is compared with that of rocky shore species.