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The in vivo response of adult northern qua- hogs, Mercenaria mercenaria ,t oAureococcus anophagef- ferens (brown tide) at the level of the gill was determined using video-endoscopy. Feeding activity, particle-approach velocities, and ventral-groove-transport velocities were documented after the quahogs were exposed to Isochryis galbana (baseline observations) supplemented with either toxic or nontoxic A. anophagefferens at two bloom concen- trations (8 10 5 or 2 10 6 cells ml -1 ). Externally, there was no evidence of adverse effects of brown tide on feeding, as siphons remained extended and dilated. Toxic brown tide at both concentrations elicited gill muscular contractions, intermittent cessation of water flow, and decreased particle loading within the pallial cavity. The 8 10 5 cell ml -1 toxic treatment had no significant effect on approach velocities or ventral-groove-transport velocities after 2 h, although time- averaging showed significant reduction of the latter during the last 30 min of exposure. The higher concentration of toxic brown tide caused a significant decrease in these velocities after only 1 h. Nontoxic brown tide produced none of these effects. Thus, A. anophagefferens compro- mised quahog feeding by stimulating contractions of the branchial musculature and interfering with lateral and ven- tral groove ciliary beating. These effects were both time- and concentration-dependent and could be caused by either a dopaminergic or a serotonergic toxic factor.

Coordinated taphonomic, geochronologic, and geochemical studies of bivalve death assemblages and their sedimentary environments of San Blas, Caribbean Panama, permit us to identify the major factors controlling skeletal degradation in mixed carbonate‐siliciclastic tropical shelf sediments. Ten sites were studied along environmental gradients including water nutrients, grain size, and sediment chemistry (carbonate, organic carbon, and reactive iron contents). Taphonomic data were derived from naturally occurring bivalve death assemblages and experimentally deployed specimens of Mytilus edulis and Mercenaria mercenaria to determine environmental controls on types and intensities of postmortem damage to skeletal hardparts and to quantify short‐term rates of damage accrual. Death assemblage shells were dated using 14C and amino acid racemization techniques to examine shell persistence, scales of time averaging, and long‐term rates of damage accrual, including correlations between shell damage and she...

The activities of both the lateral and frontal cilia of Mercenaria mercenaria were unaffected, either by the two endogenous SCP-related peptides AMSFYFPRMamide and YFAFPRQamide, or by FMRFamide (all at 10(-6) M). Dopamine (DA) inhibited the lateral cilia; the mean EC50 was 2 x 10(-6) M. The peptide YFAFPRQamide--but neither AMSFYFPRMamide nor FMRFamide--antagonized the inhibition induced by DA; this effect was dependent on both time and dose. At a DA concentration of 5 x 10(-7) M, the effect of YFAFPRQamide appeared within 20 min and became maximal within 40-60 min; the mean EC50 at these times was 4.7 x 10(-11) M. If the concentration of DA was increased to 10(-6) M, the maximal effect of the peptide was delayed to 50 min, and the mean EC50 increased to 1.1 x 10(-7) M. Particle transport by the frontal cilia was inhibited by 5-hydroxytryptamine (5HT); the mean EC50 was 5.7 x 10(-7) M. Again, only YFAFPRQamide had an antagonistic effect on the 5HT-induced inhibition. At a 5HT concentration of 10(-6) M, the effects of YFAFPRQamide did not appear until 45 min; the mean EC50 was 10(-6) M. When radioimmunoassayed with an SCP antiserum, the elution profile of a gill extract overlapped those of the SCP-related peptides that had previously been identified in extracts of whole animals. These data suggest that all three SCP analogs occur in the gill. Immunohistochemistry of the gill, carried out with a monoclonal antibody raised to SCPB, stained many varicose neuronal fibers. Most of these were associated with the gill musculature, but a sparse innervation of the filaments underlying the cilia was also observed. Some fluorescent nerve cell bodies were also seen in the gill tissue. Our results are consistent with the hypothesis that YFAFPRQamide modulates branchial activities--muscular as well as ciliary--that are associated with feeding.

Calcium and small organic molecules (e.g., tyrosine, MW 181 Da) introduced into the extrapallial fluid (EPF) of the quahog Mercenaria mercenaria exhibit rapid fluxes across the outer mantle epithelium and are distributed throughout the circulatory system within 3 h. Larger molecules (e.g., bovine serum albumin, MW 66,000 Da) are less readily exchanged between EPF and blood. The protein compositions of blood plasma and EPF are different, with at least seven protein bands expressed more prominently in the EPF. Equilibrium dialysis experiments reveal that Ca2+ constitutes only 2% of the total Ca in plasma; most of the Ca (85%) is bound to macromolecules, and the remaining 13% is present as dialyzable low molecular weight moieties. This distribution cannot be explained by speciation of inorganic Ca alone, since the MINTEQA2 equilibrium speciation model predicts that 79%-86% of the Ca should be present as Ca2+, with the remainder as CaSO4 (20%-13%). However, inclusion of a weakly Ca-binding organic molecule (log10 Ka approximately 2 M-1) into MINTEQA2 could fully reconcile modeling with experimental measurements. Results suggest that calcium transport in blood plasma and EPF is mediated by a suite of proteins and small organic ligands with a low affinity for Ca.

The origin of hemocytes, the circulating “blood cells” of bivalve molluscs, including hard clams (Mercenaria mercenaria) has not been identified (1, 2). Proliferation of hemocytes, however, can be recognized through their increased numbers in diseased animals. Proliferating cell nuclear antigen (PCNA), or cyclin, is a protein produced during the late G1 and S phases of the cell cycle (3, 4). Using antibodies that recognize PCNA in mice, we attempted to identify the origin of hemocytes in the hard shell clams. Quahog parasite unknown (QPX) is a protist that causes severe inflammation and mortality in infected clams (5, 6). We attempted to induce hemocyte proliferation by exposing clams to QPX in a 10-l water column in which 12 ml of undiluted QPX culture (at a concentration of 7p10 cells/ml) were added every 10 days; by injecting QPX between the membranous mantles and the right valves, 3 cm ventral anterior to the siphon and into the pericardial cavities (0.25 ml of undiluted QPX culture); and by injecting an inert particle (India ink, 1:10 dilution in sterile seawater [7, 8]) into the pericardial cavities. The controls consisted of two groups of clams. One group was injected with sterile seawater in the pericardial cavities; the other was untreated. Groups were sampled at 24 h, and at 1, 4, and 8 weeks after the start of the experiment. At sampling, the animals were shucked, fixed in 10% neutral buffered formalin (NBF) for 24 h, and embedded in paraffin. Sections were cut (4–6 mm), mounted onto positively charged slides (Fisherbrand, Superfrost/Plus and ProbeOn Plus slides) and stained either with hematoxylin and eosin (H&E) (9) or with anti-PCNA with a hematoxylin counterstain (Zymed, PCNA Staining Kit). Clams injected with QPX in the pericardial cavities showed mild focal inflammation associated with viable and necrotic QPX organisms. At 2 months post-injection, viable QPX organisms were no longer identified. QPX organisms and associated inflammation were not observed in clams injected in the mantle cavity. After 2 months of water column exposure, only very rare infection by QPX organs with minimal inflammation was observed in mantle tissue. India ink injection caused a minimal inflammatory response. Pools of injected ink in the tissues and vascular spaces were either engulfed by individual hemocytes or surrounded and sequestered by hemocytes (encapsulation), forming thin-walled granulomas (6, 10). Numerous individual hemocytes containing India ink were eliminated from the clams by diapedesis over lumenal epithelial surfaces (Fig. 1A). Thick-walled granulomas (6, 10) were also identified in the gills, pericardial sacs, and other 1 Worcester Polytechnic Institute, Worcester, MA.

Examination of Mercenaria mercenaria hemocyte preparations on glass coverslips showed that adherent, macrophage-like cells tended to form multinucleated giant cells morphologically similar to classical Langhans cells and foreign body inflammatory giant cells, as seen in vertebrates. The frequency of giant cell formation varied from clam to clam, possibly reflecting each animal's physiological state, as influenced by pollutant exposure, other environmental stressors and disease. Treatment of the hemocytes with concanavalin A promoted hemocyte aggregation and increased the rate of giant cell formation. Attempts to increase polykaryon formation by in vivo or in vitro phagocytic stimulation of the hemocytes were generally unsuccessful.

The hemocytes of the hard clam M. mercenaria were of three types: an agranulocyte, a small, and a large granulocyte. The agranulocyte, with only a thin periphery of cytoplasm surrounding the nucleus, had no visible cytoplasmic granules in living preparations but did exhibit a few centers of nonspecific esterase activity. This cell type represented 2% of the hemocyte population. The small granulocyte possessed four distinct granule types and comprised 61% of the total cell population. Large granulocytes accounted fro 37% of all hemocytes. While they contained the same four granule types identified in the small granulocyte, only one-third the total number were present. The nucleus of all three hemocyte types appeared morphologically similar. The four types of granules observed were a blunt, dot-like, a refractile and a filamentous granule. Blunt granules were identified as mitochondria, based on their ability to reduce Janus Green B to diethyl safranin, the presence of NADH dehydrogenase activity and boundary staining with Sudan black B. Dot-like granules were identified as lysosomes on the basis of neutral red staining, localization of acid phosphatase and nonspecific esterase activity and staining with Sudan black B. Refractile granules were demonstrated to be membrane-bound, lipid-filled structures that reacted positively with Sudan black B and Oil red O, respectively; these granules act as lipid storage centers. Nuclear similarity of the three cell types suggest that these cells might represent different stages of maturity, rather than three distinct cell lines. This was also indicated by the similar yet graded cytochemical reactions and the varying degree of motility and phagocytic activity demonstrated by hemocyte types.

Thirteen monthly measurements of individually marked juvenile (16 mm long) and adult (60 mm long) specimens of Mercenaria mercenaria (L.) from field plots in North Carolina demonstrated similar seasonal patterns in size-adjusted monthly growth rates in shell volume: a large absolute maximum occurred in spring (April or May) with smaller relative maxima in mid summer and late autumn. The ratio of juvenile to adult size-adjusted growth rates in shell volume was nearly constant for ten months but then increased eight-fold in December and January. This growth anomaly between size classes could not be explained by examining dry weights of soma and gonads from additional marked juvenile and adult Mercenaria that were sacrificed monthly. Juveniles differed from adults by possessing negligible gonadal mass on all dates. However, knowledge of monthly changes in adult gonadal mass did not explain a significant amount of the residual variation in the regression of monthly juvenile volumetric growth on monthly adult volumetric growth. Seasonal changes in growth of adult gonadal mass and quarterly examinations of gonad histology both suggested a winter period of negligible gametogenesis followed by a spring burst of intense reproductive activity. The best explanations for the anomalously high volumetric growth of juveniles relative to adults in December and January are: (1) winter availability of a food source accessible only to juveniles or (2) biochemical storage of energy during winter by adults in preparation for the process of rapid gametogenesis in spring. If the latter explanation is correct, adult Mercenaria exhibit a large seasonal change in the allocation of resources between somatic growth and reproduction with maximal allocation to reproduction in winter months before gonad histology and growth of gonadal mass indicate reproductive effort.

Buffering capacities (β) (measured in slykes = micromoles of base required to titrate the pH of 1 g wet weight of tissue by one pH unit between pH 6 and pH 7) due to nonbicarbonate buffers were measured for the tissues of three marine molluscs, the oyster, Crassostrea virginica, the cherrystone clam, Mercenaria mercenaria, and the channeled whelk, Busycotypus canaliculatum. In general β was higher in muscle tissues (adductors, foot, heart, radular retractor) than in the gill and mantle, but hepatopancreas of the whelk had a β two- to threefold higher than that of any other whelk tissue. Selected tissues (gill of oyster, catch adductor of clam, heart and hepatopancreas of whelk) showed a significant increase in buffering capacity when tissues were isolated from animals held under anoxic conditions compared with control aerobic animals; however, no consistent effect of environmental anoxia was found, nor was buffering capacity related to the tissue levels of succinate accumulated during anaerobiosis. Tissue...

The hematological parameters of Mercenaria mercenaria of similar size from two geographical areas as well as the morphology and behavior of their leucocytes were studied. On the basis of qualitative and quantitative characteristics, three types of leucocytes, designated as granulocytes, fibrocytes, and hyalinocytes, can be distinguished in both living and stained preparations.A correlation matrix computed between all parameters considered has revealed an insignificant correlation between the dimensions of whole animal and the differential count, packed cell volume, and total cell count as well as an insignificant correlation between the hematological parameters themselves. The only exception is that there is a positive correlation between the packed cell volume and the total cell count.

The extrapallial fluid (EPF), the fluid component of the shell-forming system of molluscs, has been examined for its effect on the rate of CaCO3 crystal formation in vitro. The medium was an artificial inorganic extrapallial fluid supersaturated with respect to CaCO3. EPF of the bivalves Crassostrea virginica and Mercenaria mercenaria strongly inhibited CaCO3 crystallization in high dilution. The inhibitory material had negatively charged groups as indicated by the removal of inhibition subsequent to passage through a DEAE-Sephadex column and the restoration of inhibition in material eluted from the column with 2.0 M NaCl. Polyaspartic and polyglutamic acids with COO- groups also inhibited crystal formation whereas polyamino acids lacking those groups and free amino acids were without effect. The inhibition by the acidic polyamino acids suggests that polypeptides known to be present in EPF are one possible cause of inhibition of crystal formation by EPF. Mg present in EPF was also strongly inhibitory. The...

TLC analysis of the neutral lipids in the hemolymph cells and serum of twelve specimens of Mercenaria mercenaria was performed. The serum fractions contained sterols (81%), free fatty acids (6%), sterol esters (11%), and a small amount of triglyceride (2%). Absolute amounts of chloesterol and triglyceride were 5.2-7.5 mg/100 ml and about 1 mg/100 ml, respectively. More total lipid and nearly all triglyceride was found to be in the cell fraction of the hemolymph. Cholesterol comprised 18% of the hemolymph cell sterols and 13% of the serum sterols.The five major fatty acids, in order of decreasing abundance, in the sera of specimens of Mercenaria mercenaria harvested in March and June from Buzzards Bay, Massachusetts, were C20:5, C16:0, C22:6, C18:1, and C20:1. A total of 22 fatty acids were resolved with tentative identification made for all of them. Standard deviations of the per cent composition of the major fatty acids were greater among specimens harvested in June than among those harvested in March.Th...

Laboratory studies were conducted to compare growth rates of the estuarine sand shrimp Crangon septemspinosa on various natural and artificial diets. Field studies examined the types of food consumed by the shrimp.In nature, 85% of the material in the stomach is organic debris; sand, crustacean parts, copepods, plant material and polychaetes make up the remainder. Some of the organic debris results from trituration of ingested tissues, but an undetermined portion is ingested as detritus.In the laboratory, shrimp grow rapidly on diets of Artemia salina, Mercenaria mercenaria and hard-boiled egg. Fish meal, copepods, beef liver, tropical fish food, agar enriched with glycogen, bacteria, and Spartina alterniflora detritus with associated microflora are also utilized, but growth is retarded.Crangon septemspinosa utilizes a variety of foods. The shrimp have a preference for animal tissues of marine origin and grow best on these foods, but they have the ability to utilize food of microbial and terrestrial origins.

1. The mean setting dates for larvae of Venus (Mercenaria) mercenaria grown at constant temperatures of 30.0°, 27.0°, 24.0°, 21.0° and 18.0° C. were found to lie on an almost perfectly straight line according to equation Y' = - 1.00 X + 37.91, where Y' is the predicted setting date and X is the temperature.2. There were no significant differences among the five temperature groups with respect to mean length of larvae at time of setting.3. There was no apparent relationship between maximum length of larvae at time of setting and temperature.4. The correlation between mean width and mean length of larvae at time of setting was very high (r = .95).5. No apparent relationship was found between shape of larvae (i.e., ratio of mean length to mean width) at time of setting and temperature.6. The average daily growth increment for all cultures at given temperatures under the conditions prevailing during the experiments was determined.7. The rate of growth of larvae of the southern clam, Venus (Mercenaria) campech...

In the summers of I909 and I9IO, while engaged in the study of the parasites of fishes at the laboratory of the Bureau of Fisheries, Woods Hole, Mass., I examined a number of invertebrates for larval stages of trematodes. The results of these examinations, although rather meagre with respect to the number of species found, are not without interest. The following species of mollusks were examined: Crepidula fornicata, C. plana, Ilyanassa obsoleta, Littorina littoria, L. rudis, Modiolus plicatulus, Mya arenaria, Mytilus edulis, Neverita duplicata, Pecten irradians, Purpura lapillus, Urosalpinx cineria, Venus mercenaria. Besides these several species of crustaceans were examined, also one annelid, Hydroides dianthus. Larval trematodes were found in only two species of mollusks, viz. Ilyanassa obsoleta and Pecten irradians. No trematode parasites were found in any of the crustaceans. A sporocyst found in the annelid, Hydroides dianthus, has already been reported.2

Rapid progress in studies of the morphology, physiology and ecological requirements of lamellibranch larvae, as well as other forms, can be achieved only if these organisms are easily available for study. This is seldom so in the case of lamellibranchs because the majority have a breeding period of comparatively brief duration lasting only a few months (Lebour, 1938; Thorson, 1946). During this period the larvae can be collected in plankton tows but, unfortunately, the early stages of many lamellibranchs are so alike in size and appearance that it is often impossible to distinguish with any degree of certainty the larvae of different species, or even genera. Thus, unless these larvae can be grown to metamorphosis their specific identity may remain in doubt. It is preferable, therefore, to work with larvae raised in the laboratory from fertilized eggs because in that case their identity cannot be questioned. In obtaining material for morphological and physiological studies of larvae the advantages of the direct method, i.e., the method of raising larvae in the laboratory, over the indirect method of collecting them in plankton and often only guessing their identity, are clear. However, because lamellibranch larvae are small, and because their free-swimming period is relatively long, they are difficult to culture. As a result, with the exception of a few successful attempts, mostly confined to commercially important species, such as oysters and mussels, few lamellibranchs have been grown in laboratories past the early veliger stage (Thorson, 1946). Therefore, the need for a simple but reliable method for culturing them is, of course, obvious. It is hoped that the simple but efficient method described in this article for conditioning the hard shell clam, V. mercenaria, to spawn out of season and for culturing its larvae will be applicable to many other species of lamellibranchs permitting their successful cultivation in the laboratory, where their morphological features and various aspects of behavior can be studied under controlled conditions. Realizing the importance of having a good supply of larvae for studies of the life history of Venus mercenaria, Belding (1912) tried to raise them in the laboratory. He was not successful because most of the larvae in his cultures died either before they reached the straight hinge veliger stage or soon afterwards. Belding concluded that there was no practical method for raising hard shell clams to the setting stage because of the small size and delicate nature of the eggs. Several years later, nevertheless, Wells (1927) succeeded in growing clam larvae to the setting stage. Wells, however, was mostly interested in oysters and did not continue the clam work.

1. The pH range for normal embryonic development of oysters was 6.75 to 8.75, and for clams, 7.00 to 8.75.2. More than 68% of the larvae of both clams and oysters survived at pH 6.25 to 8.75. The lower pH limit for survival of oyster larvae was 6.00 and for clam larvae, 6.25.3. The pH range for normal growth was 6.75 to 8.50 for clam larvae and 6.75 to 8.75 for oyster larvae. The rate of growth of both species dropped rapidly at pH levels below 6.75.4. The optimum pH for growth was 7.50 to 8.00 for clam larvae and 8.25 to 8.50 for oyster larvae.5. At pH 9.00 to 9.50 the percentage of eggs that developed normally, the percentage of larvae that survived, and the percentage increase in mean length of both species decreased rapidly.

1. Continuous kymograph recordings of the opening and closing of the valves of common quahogs, Venus mercenaria, secured from the Virginia coast and from Woods Hole, Massachusetts were made during February, March, April, June, and December, 1953.2. The activity records of these clams maintained under constant laboratory conditions show a persisting diurnal rhythm with maxima and minima occurring in the afternoon and early morning, respectively. There is some evidence that the pattern of the diurnal cycle varies with the time of year.3. A persisting tidal rhythm is also evident. In the group of animals for which correlations with actual tidal phases could be made, it was seen that the times of minimal activity in this cycle correspond closely with the times of low tide in the area from which the animals were collected.4. The summation of these two cycles, diurnal and tidal, is responsible for an observed lunar cycle. The phases of the lunar cycle are probably set directly by the tides to which the animals ...

The inorganic composition of the extrapallial fluids of Mercenaria mercenaria, Mytilus edulis and Crassostrea virginica was significantly different from sea water. Calcium was the principal ion bound in the extrapallial fluids. This binding was accomplished by a non-dialyzable component that appeared to be a glycoprotein.

The literature on Pelecypoda mollusks contains but few accounts of systematic studies of the changes occurring in the gonads of an animal throughout the entire year. This phase of investigation of sexual phenomena in mollusks, though neglected so far, is, however, of considerable importance and interest because, if properly carried out, it could assist greatly in the understanding of the phenomena of change of sex in some forms or add to the knowledge of the alternation of sexual phases in others. Amemiya (1929) reported a very interesting case of sex change in the Japanese oyster, 0. gigas, which was previously considered dioecious. His method consisted of making a hole in the shell of an oyster and removing through it a small piece of gonad for determination of sex. Following this the oysters were placed in cages and returned to the water for a period of one year, at the end of which they were re-examined. Meanwhile, no samples were taken for histological studies to determine what cellular changes precede the reversal of sex. Nelson (1928) gave a more or less detailed description of changes occurring in the gonads of the adult 0. virginica from April until June, but did not continue his studies through the post-spawning time and season of hibernation. In other studies dealing with sexual phenomena of the genus Ostrea, a systematic description of changes occurring in the gonads of adult animals throughout the year is also lacking. This paper deals with the changes occurring in the gonads of adult clams (Venus mercenaria) at different seasons of the annual cycle. The animals were studied for three successive years. Samples for this study were collected at bi-weekly intervals from the clam beds located near Charles Island, Long Island Sound. The depth of the water over the beds was 8-12 feet at mean low water. Since the calendar's new year, occurring in the middle of winter, coincides with the prolonged period of the animal's inactivity, it is thought convenient in this study to consider the beginning of a new year from the ecological point of view, i.e., after the completion of

1. A new apparatus, by means of which the shell activities of many bivalve mollusks can be measured and recorded, is described.2. The analysis of 399 daily records of shell activities of 47 clams, subjected to temperatures ranging from — 1.0° to 28.0° C., showed that the length of time which the animals remain open partly depends upon the temperature of the surrounding water.3. For the majority of clams hibernation begins soon after the water temperature decreases to 5.0° and 6.0° C. At lower temperatures the clams may remain completely closed for very long periods. No shell movements were exhibited, and no disposal of ejecta occurred.4. Within the temperature range of 3.9° to 10.9° C., the average period of openness increased from 4 to 88 per cent of the total time, showing a correlation with the rise of temperature.5. There was no correlation between the duration of openness of the clam shells and the temperature increase from 11.0° to 27.9° C. Within this temperature range the shells were open from 69 ...

1. A method of preparing and employing the isolated heart of the quahog, Venus mercenaria, for the bio-assay of acetylcholine (Ach) is described.2. The activities of choline and certain choline esters; of betaine and its ethyl ester; and of triethylcholine and triethyl-acetylcholine on the isolated Venus heart are compared. In further understanding the fundamental mode of action of Ach, the most significant observation was that the substitution of ethyl groups for methyl on the nitrogen of choline and Ach resulted in a complete loss of activity determined by observation on the amplitude of heart beat.

The growth and reproductive biology of the adult female stone crab, Menippe mercenaria, an economically important species in Florida, have never been investigated in the laboratory. These morphogenetic processes are influenced both by hormones and by seasonal changes in the environment. This study seeks to survey the relation between these processes, their endocrine control, and the changing environmental conditions provided in nature. Special attention has been paid to the interrelationship between growth and reproduction. This aspect has been studied by Bauchau (1961), Cheung (1966) and DA©meusy(1964, 1965a, 1965b and 1965c) in Carcinus mcienas, a boreal species. The present study employs adult female specimens of M. mercenaria since they continue to grow after reach ing sexual maturity, unlike Callinectes in which growth ceases at maturity (Truitt, 1939). The relationship between growth and reproduction was defined by (1) observ ing the occurrence of molting and spawning in a sample of the wild population; and (2) removing the eyestalks at different stages of the molting cycles and during intermolt periods occurring at different times of the year, because the eyestalks contained endocrine factors regulating these processes. Results of this study also yielded information on the life history of this species. MATERIALS AND METHODS

The heart of Venus is sensitive to acetylcholine in dilutions of 10–12 during the spring and 10–9 during the fall. It is useful as a test material for acetylcholine assay.Acetylcholine appears to leave the contracting mechanism intact and to act on the pacemaker and conducting mechanisms of this myogenic heart.Stimulation of the visceral ganglion causes inhibition in diastole resembling the effect of acetylcholine.Atropine is very toxic to the heart. In non-toxic concentrations it antagonizes neither the effect of acetylcholine nor of nerve inhibition.Fluid from a heart inhibited by visceral ganglion stimulation often depresses the beat of an eserinized test heart.Eserine prolongs the inhibition due to acetylcholine and that due to nerve stimulation. It appears likely that acetylcholine is liberated as the normal cardiac inhibitory agent in Venus.

1. Examination of the developing gonads of young clams from Long Island Sound, at two-week intervals during the first year of life, shows that a primary bisexual gonad is formed in each individual when the animal reaches the size of 4-6 mm.2. The primary gonads form from associations of germinal cells in the connective tissue, not immediately beneath the body walls but at some distance from them, at the level of the heart or slightly below it. A lumen soon appears in each gonad follicle and the germinal cells begin to proliferate rapidly.3. The primary gonad contains the antecedent cells of both sexes but the protandric nature of the primary gonad becomes manifested by the rapid proliferation of the spermatogenic cells.4. This species is not strictly protandric because few individuals develop into females without passing through a functional male phase.5. Functional sperniatozoa have been observed in the gonads of young clams, collected in October and November when only 5-7 mm. long. In some cases dischar...

1. Twelve strains of bacteria were isolated from a moribund Venus mercenaria larva in a laboratory culture. These, ten other clones, and mixed bacteria from sea water were assayed by adding broth culture yielding 106-107 cells/ml. to beaker cultures of healthy clam larvae. Only the mixed bacterial culture from the moribund larva and two of the 12 strains isolated from it caused extensive mortality. One of the virulent clones (6-) is a species of Vibrio,the other (13-1) is a Pseudomonas species.2. Larvae exposed to virulent bacteria and simultaneously treated with antibiotics were as healthy as controls, showing that active bacteria were necessary to destroy larvae and that metabolites in the bacterial inoculum were not harmful to larvae.3. Larvae were grown free of contaminating micro-organisms by allowing washed eggs to develop in antibiotic solutions and then isolating straight-hinge larvae by pipette. Either virulent clone (106-107/ml.) destroyed 10-100% of such larvae. However, exposing the animals to...

Chromosome numbers of n = 19, 2n = 38 are reported for Mercenaria mercenaria, M. campechiensis and their F1 hybrids. Meiosis is normal in the hybrids and yields no evidence of chromosome nonhomology or structural rearrangements between the two parents. The hybrids produce functional eggs and sperm which result in normal fertilization and early embryonic divisions in reciprocal backcrosses and at least some F2' s. No gross chromosomal barrier to gene exchange appears to exist between the two species.

1. Some clam eggs developed normally in concentrations of 4.0 g./l. of clay, precipitated chalk or finely ground Fuller's earth, although the percentage developing normally decreased as the concentration of these suspended materials increased.2. In silt concentrations below 0.75 g./l. the percentage of clam eggs developing normally was not significantly different from that in control cultures but decreased progressively in successively higher concentrations.3. None of the clam eggs developed normally in silt concentrations of 3.0 or 4.0 g./l.4. Larvae resulting from clam eggs developing in high concentrations of each of the suspended materials were reared to metamorphosis after being returned to normal sea water at 48 hours.5. Clam larvae were unable to grow in concentrations of clay, chalk or Fuller's earth as high as those at which some eggs developed.6. The highest concentration of chalk was 0.25 g./l. and 0.5 g./l. was the highest concentration of clay and Fuller's earth at which clam larvae showed an...

1. Whole Venus heart homogenates hydrolyze acetylcholine and benzoylcholine at a low rate.2. The enzymatic activity of such homogenates is the sum of that contributed by amoebocytes, intestinal epithelium and heart muscle.3. Isolated amoebocytes hydrolyze acetylcholine and the enzyme responsible is inhibited by 10-4 M physostigmine, thus indicating the presence of cholinesterase.4. Recently developed histochemical procedures demonstrate serum cholinesterase and lipase in amoebocytes, intestinal epithelium and heart muscle.5. Greatest lipase activity is present in the amoebocytes and intestinal epithelium, while serum cholinesterase activity is greatest in the ventricular muscle.6. The potentiation of the action of acetylcholine on the isolated Venus heart by physostigmine is due to inhibition of serum cholinesterase in the amoebocytes and especially in the heart muscle.7. The presence of varying levels of lipase in the intestinal epithelium of Venus lends support to the suggested presence of extracellular...

Reponse a l'article de J.A. Commito «Polinices predation patterns and Mercenaria morphology models» (Am. Nat 1987, vol 129 p 449-451)

DeAngelis et al. (1985) have described a model of the evolutionary response of bivalve prey to size-selective naticid snail predation. The model analyzed "the allocation of bivalve energy among reproduction, overall growth in size, and supplementary growth in shell thickness" (p. 818). Using parameter values for Polinices duplicatus as the predator and Mercenaria mercenaria as the prey, the model predicted three optimal strategies for bivalves faced with naticid predation: (1) delayed reproduction with energy diverted into rapid growth in order to reach a size refuge; (2) early reproduction, possibly with some extra shell thickness; and (3) greatly increased shell thickness for deterring predator attacks. This model and an earlier one (DeAngelis et al. 1984) are elaborations on a general qualitative model for bivalve prey (Seed and Brown 1978). [excerpt]