Hydrodynamic advantages in the free‐living spiriferinide brachiopod Pachycyrtella omanensis: functional insight into adaptation to high‐energy flow environments

Immobile benthic organisms lacking attachment or cementation mechanisms are considered to be best adapted to quiet bottom environments. Since the free‐living Lower Permian spiriferinide brachiopod Pachycyrtella omanensis inhabited a sandy substrate with high‐energy water flow, flume experiments were performed to show the possible hydrodynamic advantages of shell morphology in postural stability and generation of feeding flows. Modelling indicates that a vertical position, with the commissure plane perpendicular to the seabed, was the most unstable, although it is considered to have been its original life position. On the other hand, the passive flow inside the model in vertical position exhibited vortex movement with constant degree of inhalent flow and exhalent flow, conferring advantages on the effective filtration of food particles using a spiral lophophore. The intensity and movement of the passive flow for feeding could have been adjusted through changes in the angle of opening of the valves. As the shoreface habitat was affected by oscillatory flows, a small‐sized animal could have undergone a high risk of burial, while an increase in size would have led to easier removal from the sandy bottom. To avoid both physical risks, Pachycyrtella developed a thick shell with a high rate of growth, specifically increasing the weight of the ventral umbo without altering its morphofunction to generate passive feeding flows. Biomechanics, functional morphology, opportunistic species, Pachycyrtella, Spiriferinida, suspension feeder.     

Intermediary metabolism and shell growth in the brachiopod Terebratalia transversa

Juvenile Terebratalia transversa (Brachiopoda) metabolize carbohydrates in the anterior-most marginal mantle at a rate of 0.46 μM glucose/g/hr (in vitro incubation of mantle in C¹⁴-glucose in a carrying medium of 10^-3 M non-radioactive glucose). The rate declines to 0.18μM glucose/g/hr in full-grown specimens. Carbohydrate metabolism in the marginal (anterior-most) mantle averages approximately 3.7 times greater than metabolism in (a portion of the ‘posterior’) mantle situated between the coelomic canals and the marginal mantle. This ratio remains constant in specimens of all sizes (i.e. an ontogenetic trend in the ratio is absent at p≤ 0.05). Organic acids are not detectable within the mantle (HPLC techniques) even after simulated anoxia (N₂ bubbling during mantle incubation). Glucose metabolism in vitro declines in both the marginal and ‘posterior’ mantles during anoxia and the metabolic ratio between marginal/‘posterior’ mantles becomes 1/1. We found no difference (at p≤ 0.05) in mean metabolic activity or in sue-related metabolic trends among populations from depths ranging between mean sea level and 70 m. However, the activity within the ‘posterior’ mantle was more variable in specimens from 70 m than in those from shallower habitats (10 m - mean sea level). The size of the specimens analyzed was most variable in the groups obtained from the shallowest habitats and least variable at 70 m depth. Our results may help define the energetics of fossil as well as living brachiopod shell growth. Brachiopod shell growth is known to be very slow relative to that of bivalves and our results indicate that this is a result of the animals' slow metabolism. The inflation of the valves in T. transversa is, in part, a function of the high ratio of intermediary metabolism in the marginal vs‘posterior’ mantle (i.e. parallels the relative growth rates at the shell margin vs‘posterior’ areas). We found that the bivalve, Chlamys hastata, which is commonly associated with T. transversa, has a lower ratio of metabolic activities in the ventral/dorsal mantle areas than the brachiopod has in the anterior/posterior. The difference produces a flatter shell in the bivalve in accord with allometric principles. The higher metabolic rate in the marginal vs‘posterior’ brachiopod mantle and its more pronounced decline with anaerobiosis is reflected in the greater definition of growth increments in the outer shell layer. Our results do not support recent generalizations that correlate shell thickness of a wide variety of invertebrates inversely with metabolic rate. Growth rate as determined from width of shell growth increments is a better index of metabolic rate. Although the genetic basis of glucose metabolism is unknown, the observed metabolic variability is consistent with suggestions that populations of marine organisms living in stable offshore environments are genetically more variable but morphologically more uniform than populations from shallow water. Furthermore, our results support suggestions that bivalved molluscs and brachiopods are very different metabolically, but the data are neutral with respect to theories of competitive exclusion of the two taxa throughout geologic history.     

Metabolomic analysis of Atlantic blue crab, <Emphasis Type="Italic">Callinectes sapidus</Emphasis>, hemolymph following oxidative stress

The Atlantic blue crab, Callinectes sapidus, is an economically, ecologically, and recreationally valuable decapod crustacean that inhabits estuaries along the Atlantic and Gulf coasts of the United States. In their natural environment, blue crabs are exposed to many stressors including anthropogenic contaminants, viruses and bacteria. Bacterial infection results in the depression of oxygen uptake, and impairs normal metabolic function in a manner that has not yet been fully elucidated. Our laboratory is developing NMR-based metabolomic tools for environmental research to discover metabolomic biomarkers of stress in marine organisms. We have used NMR spectroscopy to compare the response of the crab metabolome to depression of aerobic metabolism by injection of the bacterium Vibrio campbellii, versus elevation of aerobic metabolism by treatment with 2,4-dinitrophenol (DNP), a known uncoupler of oxidative phosphorylation. The corresponding NMR spectral variations between treatments were evaluated using chemometric tools for pattern recognition and biomarker identification, including principal components analysis and partial least-squares analysis. Metabolic changes were identified in crab hemolymph 30 min after injection with V. campbellii and DNP. Glucose, considered a reliable indicator for biological stress in crustaceans, and lactate, a metabolite indicating anaerobic respiration, provided the largest variations in the metabolomes, respectively. While biological variability and/or tight regulation of the hemolymph masked subtle metabolic changes at individual time-points, metabolic trajectory analysis revealed clear differences between the two modes of oxidative stress, providing insight into the biochemical pathways involved.     

The ideal hydrodynamic form of the concavo‐convex productide brachiopod shell

Shiino, Y & Suzuki, Y. 2011: The ideal hydrodynamic form of the concavo‐convex productide brachiopod shell. Lethaia, Vol. 44, pp. 329–343. Water‐flume experiments were performed to determine whether the concavo‐convex Permian brachiopod Waagenoconcha imperfecta was hydrodynamically adapted for feeding. The generation of passive currents inside the valves was observed experimentally. The use of four transparent, hollow polyhedron models, each differing in a single morphological feature, permitted observation of the currents inside the valves and allowed evaluation of the hydrodynamic significance of the ears and the prominent geniculated trail. Regardless of the direction of ambient flow, only the approximate‐imitation model generated a stable flow pattern consisting of inhalation from the ear gapes and exhalation from the anterior trail gape; models lacking or with small changes in these morphological features failed to generate stable flow patterns. The stable flow pattern was probably maintained by a pressure difference between the posterior lower ear gapes (maximum pressure) and the anterior trail gape (minimum pressure). Notably, bilaterally rotating internal currents formed parallel to the brachial ridges; such flow patterns would facilitate the capture of food particles by the animal via tentacles on its lophophore, which is most likely were located on the brachial ridges. Our results demonstrate that the immobile brachiopod W. imperfecta, an animal incapable of widely opening its valves, probably fed on the passive internal currents generated by its shell form. This unique valve morphology appears to be perfectly adapted from a hydrodynamic point of view. □Biomechanics, ecomorphology, evolution, morphological disparity, Productidina, suspension feeder.     

MECHANICAL AND MORPHOLOGICAL PROPERTIES OF THE SHELL OF SCROBICULARIA PLANA (DA COSTA) UNDER NORMAL AND STRESS CONDITIONS

Scrobicularia plana reacts to salinity stress by closing itsvalves and respiring anaerobically. The acidic products of respirationare buffered by calcium carbonate removed from the shell. Shellmass decreases by 15% over a period of three weeks, and thereis a similar reduction in shell strength. Erosion of the shell surface, indicating buffering, takes placequickly, pits can be seen in the valves of shells at the endof six hours of normal intertidal emersion. (Received 10 February 1982;     

Osmotic changes in an estuarine bivalve,Modiolus fluviatilis

• 1.1.Responses to different salinities monitored by opening and closing of the shell valves were observed in Modiolus fluviatilis.
• 2.2.The osmotic pressure, sodium and chloride ion concentrations were measured in the haemocoelic fluid of Modiolus fluviatilis under similar conditions.
• 3.3.Free amino acids (measured as ninhydrin-positive substances) were determined in the muscle tissue of Modiolus.
• 4.4.It appears that these free amino acids are involved in the ability of the estuarine bivalve Modiolus fluviatilis to osmoregulate in a wide range of salinities.

     

The length of discontinuous gas exchange cycles in lepidopteran pupae may serve as a mechanism for natural selection

Gas exchange is studied in diapausing pupae of Mamestra brassicae L., whose larvae are reared under identical conditions. The release of CO₂ gas is recorded with infrared gaseous analyzers. Oxygen convective uptake into the tracheae and oxygen consumption rates are recorded by means of a constant‐volume coulometric respirometer. Outputs from both of these respirometry systems are combined with infrared actographs. All 3‐month‐old pupae of M. brassicae display a pattern of discontinuous gas exchange (DGE) cycles of CO₂ gas release by bursts, although the lengths of these cycles varies between individuals. Some pupae exhibit long DGE cycles of at least 20 h in duration, with negligible CO₂ gas release during interburst periods, and there is presumed to be a convective gas exchange at this time. As a result of a partial vacuum inside the tracheae, a large oxygen convective uptake always occurs at the start of the spiracular opening phase. Other pupae have short DGE cycles of less than 3 h in duration, with elevated CO₂ gas release during the interburst period, when gas exchange is predominantly diffusive. The spiracular open phase in these pupae consists of frequent separate convective bursts of CO₂ gas release, with the opening–closing rhythms of the spiracles, which are considered as O phase fluttering. The pupae with long DGE cycles exhibit extremely low metabolic rates and very low total water loss rates, whereas those with short DGE cycles have higher metabolic and total water loss rates. The pupae with long DGE cycles live approximately twice as long as those with short cycles; thus, the present study demonstrates that long DGE cycles confer a fitness benefit on pupae as a result of a lower metabolic rate associated with water economy, conferring on them a longer life.     

Temperature-dependent stomatal movement in tulip petals controls water transpiration during flower opening and closing

Temperature‐dependent tulip petal opening and closing movement was previously suggested to be regulated by reversible phosphorylation of a plasma membrane aquaporin ( Azad et al., 2004a ). Stomatal apertures of petals were investigated during petal opening at 20°C and closing at 5°C. In completely open petals, the proportion of open stomata in outer and inner surfaces of the same petal was 27 ± 6% and 65 ± 3%, respectively. During the course of petal closing, stomatal apertures in both surfaces reversed, and in completely closed petals, the proportion of open stomata in outer and inner surfaces of the same petal was 74 ± 3% and 29 ± 6%, respectively, indicating an inverse relationship between stomatal aperture in outer and inner surfaces of the petal during petal opening and closing. Both petal opening and stomatal closure in the outer surface of the petal was inhibited by a Ca²⁺ channel blocker and a Ca²⁺ chelator, whereas the inner surface stomata remained unaffected. On the other hand, sodium nitroprusside, a nitric oxide donor, had no effect on stomatal aperture of the outer surface but influenced the inner surface stomatal aperture during petal opening and closing, suggesting different signalling pathways for regulation of temperature‐dependent stomatal changes in the two surfaces of tulip petals. Stomata were found to be differentially distributed in the bottom, middle and upper parts of tulip petals. During petal closing, water transpiration was observed by measuring the loss of ³H₂O. Transpiration of ³H₂O by petals was fivefold greater in the first 10 min than that found after 30 min, and the transpiration rate was shown to be associated with stomatal distribution and aperture. Thus, the stomata of outer and inner surfaces of the petal are involved in the accumulation and transpiration of water during petal opening.     

Combining reverse genetics and nuclear magnetic resonance‐based metabolomics unravels trypanosome‐specific metabolic pathways

Numerous eukaryotes have developed specific metabolic traits that are not present in extensively studied model organisms. For instance, the procyclic insect form of Trypanosoma brucei, a parasite responsible for sleeping sickness in its mammalian‐specific bloodstream form, metabolizes glucose into excreted succinate and acetate through pathways with unique features. Succinate is primarily produced from glucose‐derived phosphoenolpyruvate in peroxisome‐like organelles, also known as glycosomes, by a soluble NADH‐dependent fumarate reductase only described in trypanosomes so far. Acetate is produced in the mitochondrion of the parasite from acetyl‐CoA by a CoA‐transferase, which forms an ATP‐producing cycle with succinyl‐CoA synthetase. The role of this cycle in ATP production was recently demonstrated in procyclic trypanosomes and has only been proposed so far for anaerobic organisms, in addition to trypanosomatids. We review how nuclear magnetic resonance spectrometry can be used to analyze the metabolic network perturbed by deletion (knockout) or downregulation (RNAi) of the candidate genes involved in these two particular metabolic pathways of procyclic trypanosomes. The role of succinate and acetate production in trypanosomes is discussed, as well as the connections between the succinate and acetate branches, which increase the metabolic flexibility probably required by the parasite to deal with environmental changes such as oxidative stress.     

Studies in Stomatal Behaviour: VII. EFFECTS OF ANAEROBIC CONDITIONS UPON STOMATAL MOVEMENT--A TEST OF WILLIAMS'S HYPOTHESIS OF STOMATAL MECHANISM

An experiment was carried out to investigate stomatal responsesin wheat to four ‘closing treatments’, viz. highcarbon dioxide concentration, darkness, dry air and nil, eachgiven under both aerobic and anaerobic conditions. Thus theeffect of lack of oxygen on the closing (or opening) tendencywas estimated. Changes in calculated from resistance porometer readings were used as data and reasonsare given for thinking this is the best available measure forinvestigating stomatal dynamics in wheat. Williams's hypothesisdemands that lack of oxygen should cause stomatal opening orprevent closure; the present experiment shows that anaerobicconditions significantly increase the closing tendency when‘closing treatments’ are first applied. There isalso some suggestion that oxygen-lack itself tends to causeclosure in the absence of any other ‘closing treatment’.Williams's hypothesis in its original form is thus disproved(for wheat) but the present results would be consistent withan ‘active’ uptake of water by the guard cells contributingto stomatal opening. A nearly significant interaction betweencarbon dioxide and oxygen suggests that under anaerobic conditionsa ‘closing substance’ may perhaps be formed, forexample, by the union of some intermediate in glycolysis withcarbon dioxide.     

Guard Cell Metabolism in Epidermis of Commelina communis L. During Stomatal Opening and Closing

The rates of CO² incorporation into the epidermis of C. communiswere linear and were similar during the completion of opening(2 h) and closing (1 h) movements of stomata. The kinetics of¹⁴C turnover between metabolites and the rates of ‘leakage’of metabolites were determined for opening and closing movements.When stomata were opening there was a slow turnover of ¹⁴C frommalate chiefly into sugars. Upon stomatal closure ¹⁴C was initiallymainly in sugars, malate, and sugar phosphates. Thereafter,there was a slight loss of label from sugar phosphates witha corresponding increase in malate. Starch became labelled duringopening and closing movements. Rates of incorporation of CO₂found in the ‘leakage’ fraction were greatest whenstomata were opening. Of the labelled compounds Most‘from the tissue, malate was the most highly labelled whetherstomata were opening or closing. Although interpretation of the turnover patterns is difficultwithout knowledge of pool sizes for the metabolites it is suggestedthat a pool of sugars exists within the guard cells, which havefairly direct and reversible access to carbon from starch andmalate. The implications of loss of malate from guard cellsduring stomatal opening and closing are discussed.     

The first scallop

Scallops (Pectinidae) are a highly diverse bivalve family with a long evolutionary history, but insufficient knowledge on the internal shell characters of initial taxa has hampered clarification of their phylogenetic roots. Here, morphological details of the shell interior of the basal pectinid Pleuronectites laevigatus from the Middle Triassic are documented for the first time. It is shown that ligament morphology, lack of internal buttresses and hinge articulation, presence of a right anterior auricular scroll, procrescent discs, and differential valve convexity of Pleuronectites link Pectinidae with Early Triassic aviculopectinoids rather than with entoliids, as recently proposed. The key adaptations of Pectinidae, i.e. the ctenolium and the alivincular-alate ligament system, probably evolved in conjunction with a marked size increase that required improvements in the shell attachment and in the system for opening the valves. Although Pleuronectites laevigatus is recognized as the earliest known member of the Pectinidae, a diphyletic origin of this family from different stocks within the Aviculopectinoidea cannot be ruled out.     

The chemiosmotic model of stomatal opening revisited

Stomata are light‐activated biological valves in the otherwise gas‐impermeable epidermis of aerial organs of higher plants. Stomata often regulate rates of photosynthesis and transpiration in ways that optimize whole‐plant carbon gain against water loss. Each stoma is flanked by a pair of opposing guard cells. Stomatal opening occurs by light‐activated increases in the turgor pressure of guard cells, which causes them to change shape so that the stomatal pore between them widens. These increases in turgor pressure oppose increases in cellular osmotic pressure that result from uptake of K⁺. K⁺ uptake occurs by a chemiosmotic mechanism in response to light‐activated extrusion of H⁺ outward across the plasma membrane of the guard cell. The initial changes in cellular membrane potential lead to the opening of inward‐rectifying K⁺ channels, after which K⁺ is taken up along its electrochemical gradient. Changes in membrane potential resulting from K⁺ uptake may be balanced by accumulation of Cl^?ions by guard cells and/or by synthesis of malic acid within each cell. Malic acid also acts to buffer increases in cytosolic pH caused by H⁺ extrusion. This review describes how the application of patch‐clamp technology to guard cell protoplasts has enabled investigators to elucidate the mechanisms by which H⁺ is extruded from guard cells, the types of ion channels present in the guard cell plasma membrane, how those ion channels are regulated, and the signal transduction processes that trigger stomatal opening and closing.     

Shell decay rates of native and alien freshwater bivalves and implications for habitat engineering

1. Spent shells of bivalves can provide habitat for other organisms, as well as playing important roles in biogeochemical cycles. The amount of spent shell material that will accumulate at a site depends on rates of both shell production and decay, although the latter is rarely considered. 2. We measured the instantaneous decay rates of four species of freshwater bivalves across a range of sites in south‐eastern New York, and found that rates varied by more than 500‐fold across sites and species. 3. Differences in decay rates were related to water chemistry (Ca, pH, dissolved inorganic C), the presence of a current, and the size of the bivalve shell. 4. Combining these decay rates with estimates of shell production derived from the literature, we conclude that the Unionidae, Corbicula, and Dreissena are all capable of producing large accumulations (>10 kg dry mass m⁻²) of spent shells, while members of the Sphaeriidae probably rarely will produce such large accumulations. 5. Hence the replacement of native unionid bivalves by the alien Corbicula and Dreissena may have little effect on standing stocks of spent shells, unless the aliens invade sites where unionids are scarce or absent.     

Tight Junction Dynamics: Oscillations and the Role of Protein Kinase C

The present study aimed to characterize the role of protein kinase C (PKC) on the dynamics of tight junction (TJ) opening and closing in the frog urinary bladder. The early events of TJ dynamics were evaluated by the fast Ca⁺⁺ switch assay (FCSA), which consisted in opening the TJs by removing basolateral Ca⁺⁺ ([Ca⁺⁺] _bl ), and closing them by returning [Ca⁺⁺] _bl to normal values. Changes in TJ permeability can be reliably gauged through changes of transepithelial electrical conductance (G) determined in the absence of apical Na⁺. The FCSA allows the appraisal of drugs and procedures acting upon the mechanism controlling the TJs. The time courses of TJ opening and closing in an FCSA were shown to follow single exponential time courses. PKC inhibition by H7 (100 μm) caused a reduction of the rate of junction opening in response to removing [Ca⁺⁺] _bl , without affecting junction closing, indicating that PKC is a key element in the control of TJ opening dynamics in this preparation. H7 at 250 μm almost completely inhibits TJ opening in response to basolateral Ca⁺⁺ withdrawal. Subsequent H7 removal caused a prompt inhibition release characterized by a sharp G increase which, however, once started cannot be stopped by H7 reintroduction, Ca⁺⁺ being necessary to allow TJ recovery. A step rise of apical Ca⁺⁺ concentration ([Ca⁺⁺] _ap ) causes a reduction of the rate of TJ opening in a FCSA, an effect that is believed to be mediated by apical Ca⁺⁺ entering the open TJs. The specific condition of having Ca⁺⁺ only in the apical solution and the TJs located midway between the Ca⁺⁺ source (apical solution) and the Ca⁺⁺-binding sites presumably located at the zonula adhaerens, might configure a situation in which a control feedback loop is set up. A rise of [Ca⁺⁺] _ap during the phase of G increase in an FCSA causes a transient recovery of G followed by a subsequent escape phase where G increases again. Oscillations of G also appear in response to a rise of apical Ca⁺⁺. Both escape and oscillations result from the properties of the TJ regulatory feedback loop. In conclusion, the present results indicate that PKC plays a key role in TJ opening in response to extracellular Ca⁺⁺ withdrawal without major effect on the reverse process. In addition, PKC inhibition by H7 not only prevents TJ opening in response to basolateral Ca⁺⁺ removal but induces a prompt blockade of TJ oscillations induced by apical Ca⁺⁺, oscillations which reappear again when H7 is removed. Received: 9 May 2000/Revised: 30 August 2000     

Validation of a Fluid–Structure Interaction Model of a Heart Valve using the Dynamic Mesh Method in Fluent

Simulations of coupled problems such as fluid–structure interaction (FSI) are becoming more and more important for engineering purposes. This is particularly true when modeling the aortic valve, where the FSI between the blood and the valve determines the valve movement and the valvular hemodynamics. Nevertheless only a few studies are focusing on the opening and closing behavior during the ejection phase (systole). In this paper, we present the validation of a FSI model using the dynamic mesh method of Fluent for the two-dimensional (2D) simulation of mechanical heart valves during the ejection phase of the cardiac cycle. The FSI model is successfully validated by comparing simulation results to experimental data obtained from in vitro studies using a CCD camera.     

Protein Synthesis during Endogenous Rhythmic Leaflet Movement in Albizzia

A rhythm was found in protein synthesis accompanying rhythmic leaflet opening and closing in the dark in the plant Albizzia. More protein was synthesized during the opening of the leaflets than during the closing. Furthermore, an inhibitor of protein synthesis, cycloheximide, prevented rhythmic opening of leaflets but had no effect on rhythmic closing. It is suggested that protein synthesis is involved in the movement across membranes of K⁺ ions that cause turgor changes and leaflet movement.     

Biology and functional morphology of a new species of endolithic Bryopa (Bivalvia: Anomalodesmata: Clavagelloidea) from Japan and a comparison with fossil species of Stirpulina and other Clavagellidae

Abstract. A new species of Clavagellidae, Bryopa aligamenta, from Okinawa, Japan, is described. The species is endolithic in living corals, with the left valve cemented to the crypt wall, as in all clavagellids. The free right valve exhibits an unusual growth pattern, with commarginal lines seemingly arising from the posterior valve margin and extending towards the anterior. This results from: (i) progressive anterior erosion of the umbones, probably as a consequence of the boring process; (ii) the apparent migration posteriorly, as the umbones are eroded, of the dorso‐ventral growth axis of the shell; and (iii) enhanced posterior inter‐commarginal growth. Unlike other clavagellid genera and species, however, there is no discernible primary ligament, at least in the adult. It is possible, however, that if a juvenile ligament were present (as in B. lata), it too would be lost as a consequence of antero‐dorsal erosion during boring. To retain valve alignment in the absence of a primary ligament, and possibly upon reaching an adult size, the mantle lays down alternating layers of calcium carbonate and proteinaceous periostracum onto the interior surface of the shell to thicken it, most noticeably marginally and, especially, posteriorly. The two valves are united dorsally, therefore, by thin layers of periostracum that probably exert a minimal opening force. B. aligamenta is, however, further characterised by large adductor, pallial, and siphonal retractor muscles so that the entire animal is encased tightly within an internally strengthened shell within a crypt. Movement must be minimal, blood being pumped into pallial haemocoels to push open the valves and extend the siphons. Despite a suggestion to the contrary, Bryopa is retained in the Clavagellidae, its unusual growth processes resulting from an endolithic life style within living corals. The fossil clavagellid Stirpulina bacillus, from the Pliocene/Pleistocene of Palermo, Sicily, Italy, was, unlike Bryopa aligamenta and other clavagellids, endobenthic, with a long adventitious tube and anterior watering pot superficially similar to species of Penicillidae, another family of the Clavagelloidea. Furthermore, as in all clavagellids only the left valve is fused into the fabric of the tube, the right being free within it. In all penicillids, both valves are fused into the fabric of their tubes. The watering pots of the fossil S. coronata, S. vicentina, and S. bacillus, moreover, are formed in a different manner to that of penicillids, by progressive encasement of the right valve inside the tube. In penicillids, the tube is secreted in a single event from the general mantle surface and the incorporation of both valves into its fabric. The constituent genera of the Clavagellidae thus constitute an example of parallel evolution with members of the Penicillidae.     

Temporal dynamics of morphologic diversity of the Japanese scallop <Emphasis Type="Italic">Mizuhopecten Yessoensis</Emphasis> (Jay, 1856)

The temporal diversity of 11 morphological features of both shell valves in eight cultivated samples of the Japanese scallop M. yessoensis from Alexeev Bay (Popov Island, Sea of Japan) at different ages and from different generations was analyzed. The sample diversity with respect to each investigated feature was observed. The sample differences in the studied features as well as shell valve variability within the sample were demonstrated to be determined by both mollusk age and sample generation. This phenomenon is considered to be the result of differences in the environmental influence on each mollusk generation under constant technological conditions.     

Comparison of routine metabolic rates of the stygobite, Gammarus acherondytes (Amphipoda: Gammaridae) and the stygophile, Gammarus troglophilus

1. Reduced metabolic rate among cave organisms compared with surface species has long been suggested as an adaptation to food shortage in cave environments. However, comparisons of metabolic rates between species have not often included closely related surface and cave species. By measuring metabolic rate across three seasons and over a range of body sizes, we examined the hypothesis that the routine metabolic rate of Gammarus acherondytes, a federally listed stygobitic amphipod, is lower than that of the closely related stygophilic Gammarus troglophilus. To determine if human activities increased the supply of organic matter to caves, we also examined the relationship between residential development and bacterial contamination in water wells. 2. For G. acherondytes, the slope of the overall relationship between oxygen consumption and body dry mass did not differ from zero and did not vary seasonally, whereas for G. troglophilus it was positive and higher in summer than in winter and spring. These results provide insights into a potential novel metabolic adaptation among stygobites. Higher metabolic rate in young G. acherondytes would allow efficient use of typically transient energy sources and a low metabolic rate at larger body sizes would increase survival through periods of food scarcity. 3. The number of wells with faecal coliform contamination was weakly but positively correlated with the number of residential building permits, indicating that surface land‐use changes probably increase the availability of energy in groundwater systems inhabited by G. acherondytes. This may give stygophilic animals, with higher metabolic rates, a competitive advantage in the caves, thus reducing the abundance of stygobites such as G. acherondytes.