Consumption of diatoms and diatom filtrates by the tentaculate deposit-feederEupolymnia nebulosa (Annelida: Polychaeta)

Rates of organic uptakes of three live diatoms (Nitzschia acicularis, Nitzschia sp. andNavicula incerta), and of three corresponding filtrates by the deposit-feeding polychaeteEupolymnia nebulosa (Montagu) were measured under similar experimental conditions. Worms used during this study were collected by SCUBA diving at Port-Vendres in shallow water (7 m deep) during the summer of 1986. Uptake rates of live diatoms were affected both by length of the experiments and by the nature of the food offered. The highest rate of uptake (11.8 10^–4 mg algal ash-free dry wt mg^–1 worm dry wt h^–1) was recorded during a short-term experiment (4 h) with the smallest diatom (Nitzschia sp.). The lowest rate (1.1 10^–4 mg algal ash-free dry wt mg^–1 worm dry wt h^–1) was recorded during a long-term experiment (48 h) with the largest diatom (Nitzschia acicularis). Filtrates ofN. acicularis were more readily utilized than those ofNitzschia sp. andNavicula incerta. Because of differences in uptake rates of algal filtrates as a function of species, it is not possible to evaluate the bias due to interaction with dissolved substances in experimental studies assessing ingestion of live benthic diatoms byE. nebulosa.     

Feeding responses of the tentaculate deposit-feederEupolymnia nebulosa (Annelida: Polychaeta): Influence of sexual maturity

Feeding responses of the tentaculate depositfeeding polychaeteEupolymnia nebulosa (Montagu) were studied by measuring rates of uptake of three different¹⁴C-labelled diatoms (unialgal cultures ofNavicula incerta Grunow,Nitzschia acicularis Wm Smith, andNitzschia sp.). Worms used during this study were collected in the harbor of Port-Vendre (Western Mediterranean) during August 1986 (immature worms) and December 1987 (mature worms). Uptake rates were affected both by the length of the experiments and by the nature of the food offered. The highest rate of uptake (2.98 10^–4 mg ashfree dry wt of algae mg^–1 dry wt of worms h^–1) was obtained during short-term experiments (4 h) with the smallest diatom (Nitzschia sp.). The lowest rate of uptake (0.21 10^–4 mg ash-free dry wt of algae mg^–1 dry wt of worms h^–1) was also obtained withNitzschia sp., but for a long-term (48 h) experiment. There was no significant difference between rates of uptake of immature and mature worms.     

Reproductive behaviour ofNereis diversicolor (Annelida: Polychaeta)

Nereis diversicolor O. F. Müller, collected on the tidal flats of the Jadebusen (North Sea, FRG) in autumn 1987 and 1988, was exposed to different temperatures in the laboratory. Results indicated that maturation was induced by temperatures above 6°C; spawning in early spring was synchronized by raising temperatures after a period of low temperatures in winter, and occurred mainly at new and full moon. During reproduction the female stays inside the burrow; the male releases sperm in front of it; the resultant larvae remain in the tube for 10 to 14 d protected by the female.     

An investigation on the anaerobic metabolism of Nephtys hombergii (Annelida: Polychaeta)

In Nephtys hombergii Savigny (Annelida: Polychaeta: Errantia), succinate and less pronounced L-alanine are accumulated as endproducts during an initial phase of anaerobiosis. In this phase aspartate is utilized as substrate for anaerobic energy production in addition to glycogen. Prolonged anaerobiosis results in the formation of propionate and acetate which, to a large extent, are excreted into the water. The concentrations of aspartate and succinate were found to remain unchanged down to a Pw_{O 2}(oxygen partial pressure in incubation water) of approximately 20 torr, indicating a fully aerobic metabolism. At a Pw_{O 2}of 15 torr characteristic changes can be observed: energy production becomes partially anaerobic. At a Pw_{O 2}of 7 torr the level of aspartate is largely reduced, but the accumulation of succinate is still significantly less than at anoxia. [In the habitat of N. hombergii, the intertidal mud flats, a Pw_{O 2}in the range from 0 torr (Pamatmat, 1968) to 12 torr (Wells and Warren, 1975) was measured.] The activities of some important enzymes involved in anaerobic energy production (among them pyruvate kinase, phosphoenolpyruvate carboxykinase and lactate dehydrogenase) were measured. Although N. hombergii has a high glycolytic capacity, no lactate dehydrogenase was detected. Instead strombine and alanopine dehydrogenases were present in comparatively high activities.     

Nachweis der epitokie als fortpflanzungsmodus des polychaeten Eunice siciliensis (Polychaeta: Annelida)

Eunice siciliensis (Grube)¹ is a sedentary polychaete with separate sexes; its germ cells develop only in the posterior part of the body. In March and April, females with whitish or even dark-green oocytes, males with only few spermatogonia, and individuals with no germ cells at all were discovered in the “coralligène” of the Banyuls region (European Mediterranean Sea). In august, besides immature and sexually non-differentiated worms, mature individuals of both sexes were captured: females with dark bluish-green oocytes of diameters up to 250μm, and males with milky genital segments containing spermatozoa. Soon after isolation from the substrate, these individuals performed characteristic movements with their posterior body parts, which then autotomized, and released ova and spermatozoa. Evidence is given that the anterior, atokous body parts survive in their tubes in the “coralligène” after separation from the epitokous portions, and regenerate new genetal segments. The development of gametes observed in these regenerated segments indicates the ability of E. siciliensis to reproduce more than once during its lifetime. Not only caudal, but also prostomial regeneration was observed; the formation of a (morphologically different) secondary prostomium appears to be essential for any development of germ cells in worm fragments. E. siciliensis exhibits surprising similarities in habits and in formation of an epitokous form with Eunice viridis (Gray), the “palolo” worm of the South Pacific Ocean, but nevertheless, lacks the prominent criteria of this famous species: the ventral eye spots on each genital segment in males and females, and the paired areas with brown pigmentation on the ventral side of each epitokous segment in the males.     

An ultrastructural study of Crassostrea angulata (Mollusca,Bivalvia) spermatogenesis

The cytoplasm of Crassostrea angulata (collected from the Atlantic coast of Northern Spain, Galiza, between 1992 and 1993) spermatogonia contains a few proacrosomal dense vesicles and intermitochondrial round granulo-fibrillar dense bodies. In primary spermatocytes, large cytoplasmic spaces appear occupied by large round and more scattered granulo-fibrillar dense bodies which are intermingled with cord-like dense structures and are in close association with mitochondria and the rough endoplasmic reticulum. As a result of Golgian activity, the number of dense proacrosomal vesicles increases and a flagellum arises from the centrioles. During the second meiotic division, several round dense bodies surrounding cord-like dense structures as well as dense proacrosomal vesicles, were observed between chromosomes. During spermiogenesis, no Golgian activity was noticed, and only the rough endoplasmic reticulum was observed in close association with proacrosomal vesicles. Similar results were observed for Ostrea edulis (collected from the Atlantic coast of southern Portugal, Algarve, between 1992 and 1993). Spermatozoa of both species are of the aquasperm type, and although their ultrastructure is quite similar, silver and phosphotungstic acid-chromic acid stainings enabled us to clearly distinguish both species at the ultrastructural level. The different morphological aspects of spermatogenesis in the Pteriomorphia and the use of silver and PTA stainings in the Mollusca are reviewed and discussed.     

Le caryotype d'Aulacomya ater regia (Mollusca: Bivalvia: Mytilidae) des Iles Kerguelen

In 1983, specimens of the antarctic mussel Aulacomya ater regia Powell, 1957 were collected from the Kerguelen Islands and transported alive to the Zoological Station in Villefranche-sur-Mer, France. The chromosome complement of the mussel, as determined from branchial tissue, was found to consist of 13 pairs of chromosomes with terminal or subterminal centromeres. This species differs from the other species of Mytilidae studied up to the present in the number and the morphology of the chromosomes. A. ater regia is also unique among the known bivalves in displaying only terminal or subterminal centromeres.     

Levels of genetic polymorphism at two enzyme encoding loci in eight species of the genus Macoma (Mollusca: Bivalvia)

Levels of genetic polymorphism were surveyed at two enzyme loci (LAP, PGI) in 2 intertidal and 6 subtidal species of the bivalve genus Macoma living in the waters of the San Juan Islands (Washington and Canada). The temporal environmental variability-genetic variability hypothesis predicts that intettidal species should have greater levels of genetic polymorphism than subtidal species. This is not true for the genus Macoma. However, at the PGI locus, genetic polymorphism was proportional to niche breadth in both the intertidal and subtidal species, but only for intertidal species at the LAP locus. These results support the contention that temporal environmental variability is not necessarily important in maintaining genetic variability, but that environmental heterogeneity may select for increased polymorphism at some loci.     

Variability of the frequency of male neoteny in Ostrea puelchana (Mollusca: Bivalvia)

Ostrea puelchana (D'Orbigny), a larviparous oyster from the Atlantic coast of South America, comprises two types of individuals: (1) adults which live for several years and become sexually developed after one year, these show a rhythmic successive hermaphroditism with male, hermaphroditic and female phases; (2) neotenic individuals settled on the adults, which live for only about one year and function exclusively as males. Adult oysters were collected in February 1982 from a natural bed in the San Matias Gulf, Argentina, and were transferred to two sites 200 km to the south of their original habitat, where they were maintained under culture conditions. At the beginning of the study, 17% of adult oysters were observed bearing neotenic individuals. After two years, the number of adults in the female phase had decreased, and neotenic individuals had entirely disappeared. The presence of female-phase adults would seem to be necessary for the existence of neotenic males. Further analysis of the results revealed high adult density to be directly associated with greatly decreased numbers of adults in the female phase; this may play a role in the decrease of neotenic individuals.     

Uptake,binding and clearance of divalent cadmium in Glycera dibranchiata (Annelida: Polychaeta)

The bloodworm Glycera dibranchiata Ehlers, 1968 accumulates cadmium through the general body surface and the intestine. Absorption through the gut accounts for cadmium which rapidly binds to coelomic proteins. Intracoelomic injection of ¹⁰⁹Cd demonstrates that cadmium binds readily to hemoglobin and other proteins. The degree of cadmium binding is pH-dependent. The apparent pK of binding sites in body wall and musculature homogenates is 5.39. Cadmium ions injected into the coelom at 7 g g^-1 tissue increase proline incorporation rates into the positively charged hemoglobin (cathode fraction) by 15-fold in 3 days. A 3-fold increase of proline incorporation was observed in the anode hemoglobin fraction over the same time period. Radioactivity in various protein fractions decreases at different rates after injection of ¹⁰⁹Cd. Comparisons between the function of mammalian metallothionein and the coelomic fluid proteins of G. dibranchiata as a detoxification mechanism are discussed.     

Rates of seasonal sediment reworking in Axiothella rubrocincta (Polychaeta: Maldanidae)

Sediment reworking rates of Axiothella rubrocincta (Johnson, 1901) (Polychaeta: Maldanidae) were measured in situ in Tomales Bay, California (USA), from August, 1969 through July, 1970. On the average, each adult worm (approximate fresh weight=1 g) reworks about 5 g dry sediment d^-1 at a mean temperature of 13.4°C and a mean salinity of 31.8.Reworking rates are positively correlated with temperature and salinity, and negatively with sediment organic carbon, sedimentation rates and grain size. An inverse correlation exists between sediment reworking rates (g dry sediment g^-1 wet wt of worm d^-1) and g wet weight of worm. Sediment parameters deseribing unworked sediments are not significantly different from those for fecal sediments. Although these data suggest this species to be a non-selective deposit-feeder, it is more likely that it is faculatively selective.     

Digestion and assimilation of protein by Mytilus trossulus (Bivalvia: Mollusca) fed mixed carbohydrate/protein microcapsules

Cross-linked walled protein microcapsules have previously been developed and shown to be ingested, digested and assimilated by suspension-feeding bivalves. In this study, we examined the effect of adding carbohydrate to protein capsules on the utilization of encapsulated protein by mussels (Mytilus trossulus) in a series of in vitro enzyme incubations and an in vivo feeding experiment. Two types of carbohydrate (amylose and maltodextrin) were separately encapsulated at a carbohydrate to protein ratio of 1:1 by weight. In vitro carbohydrate and protein leakage rates from mixed carbohydrate/protein capsules were low [e.g. <4% (24h)^-1] compared to previously reported leakage rates for protein capsules [e.g. 5 to 20% (24h)^-1]. Proteolytic breakdown of mixed carbohydrate/protein capsules by mussel-style extracts was similar to that for protein capsules, when the encapsulated carbohydrate was amylose, a straight-chain (-1,4-linkage) polysaccharide; however, capsules containing maltodextrin, which is partially comprised of -1,6-linkages, were not as readily digestible in vitro. In contrast to results from in vitro enzyme assays, maltodextrin/protein capsules were utilized in vivo by mussels with similar efficiencies to those for protein and amylose/protein capsules. These findings demonstrate that utilization of microencapsulated protein by mussels cannot be accurately predicted from results of in vitro enzyme assays. Importantly, up to 50% of the dry weight of cross-linked walled protein microcapsules can be replaced with carbohydrate without significantly affecting encapsulated protein digestion and assimilation efficiencies for M. trossulus.     

Temperature-time relationships for survival of embryos and larvae of Mulinia lateralis (Mollusca: Bivalvia)

The influence of temperature over 8 time intervals on survival of cleavage stages, trochophore larvae, and straighthinge veliger larvae of Mulinia lateralis (Say) was investigated using a thermal gradient apparatus. There was a direct relationship of mortality with increased period of exposure. As the clams aged, temperature tolerance increased, with cleavage stages being most sensitive to higher temperatures and straight-hinge larvae least sensitive. Multiple-regression equations were developed to allow prediction of percentage mortalities under different conditions of temperature and time exposure. Entrainment of M. lateralis embryos and larvae in the cooling-water systems of steam-electric power plants should be as short as possible to keep mortality toa minimum.Contribution No. 550 of the Natural Resources Institute, University of Maryland, and Contribution No. 531 of the Virginia Institute of Marine Science.     

Effects of temperature on oocyte growth in the Mediterranean terebellid Eupolymnia nuebulosa (Annelida: Polychaeta)

Eupolymnia nebulosa (Montagu) is a widely distributed terebellid polychaete that builds its tubes on the coastal shelf in areas with mixed soft and hard bottoms. From a long-term survey in the Bay of Banyuls, France (NW Mediterranean), we found an advancement of the timing of the spawning period coincident with a delayed breakdown of the thermocline. We postulate that persistent high temperatures can influence gamete development by stimulating oocyte growth, resulting in earlier spawning. During 1992 and 1993, we used a between-individuals experimental approach to assess the possible effect of temperature on oocyte growth based on: (1) determination of the growing fraction of the oocyte population (i.e. oocyte net growth); (2) identification of differences in oocyte growth-rate among females; (3) comparison of non-significantly different size-distributions of the growing oocyte fraction (net oocyte size-distributions) at the beginning of the experiments with those at the end. No effect of temperature on oocyte growth was detectable at the population level, but a positive individual response to prolonged high temperature was evident. Thus, the lack of a significant response by the population to prolonged high temperature does not imply a lack of individual response. We propose a model of oocyte-growth dynamics based on temperature that incorporates previous observations of extended oogenesis and oocyte growth during periods of both increasing and decreasing temperature and on the scattered pattern of oocyte size-distributions at the onset of spawning. Received: 4 November 1996 / Accepted: 18 January 1997     

Co-ordinated rhythms of digestion,absorption and excretion in Mytilus edulis (Bivalvia: Mollusca)

Sequential alternation of extracellular digestion in the stomach and intracellular digestion in the diverticula appears widespread among bivalves. The present study documents some physiological consequences of such processes in Mytilus edulis L. collected during 1981 from Whitsand Bay, Cornwall, England. Pronounced temporal fluctuations in faecal deposition are described that relate, in terms of amplitude and period, to both sinusoidal rhythmicity established for ammonia excretion and changes in the morphology of digestive tubules. Although at least partially synchronised among replicate groups of mussels, these cycles bore no consistent relationship with exogenous influences. Hourly fluctuation in the net absorption efficiency for nitrogen, as evidenced by the mean percentage ±2 SE, measured over 24 h sampling periods, was considerable (16.0±53.7, 49.3±10.9 and 52.8±6.6 for mussels acclimated in March, June and October, respectively). This variation in absorption derived from an inverse relationship between the percentage nitrogen within faeces and the rate of faecal egestion. Accordingly, peaks of faecal deposition presumably represented the pulsed remnants of intracellular digestion. Co-ordinated rhythms of digestion, absorption and excretion were thus evident in M. edulis. These processes displayed seasonally dependent periodicities of approximately 8, 3 and 4 h in March, June and October, respectively. It was concluded that, at least for M. edulis, this previously unquantified rhythmicity of physiological processes warrants careful consideration during assays commonly undertaken in the complication of nutrient and energy budgets.     

Cysteine-glutathione disulfide, the sperm-release pheromone of the marine polychaete Nereis succinea (Annelida: Polychaeta)

Summary. In the marine polychaete Nereis succinea (Frey & Leuckart 1847) a sex pheromone was isolated from the coelomic fluid of sexually mature females and identified by NMR studies and independent synthesis. This pheromone is released by the females during reproduction together with eggs and coelomic fluid into the free water column and induces sperm release of surrounding males. Its structure was ascertained as L-cysteine-glutathione disulfide. It exhibited a response threshold of 0.6 · 10⁻⁷ M. Received 15 July 1997; accepted 25 November 1997.     

Freshwater Mussel,Lamellidens Marginalis (Lamarck) (Mollusca: Bivalvia: Unionidae) As an Indicator of River Pollution

Abstract

Analyses were made of heavy metals, manganese, nickel, copper, zinc and lead in water samples and soft body, shell and different tissues (gills, digestive glands, mantle and viscera) of the Unionid mussel, Lamellidens marginalis collected from two tributaries of the Cauvery river. Water samples from Station I contained higher concentrations of the metals than those from Station II. the concentration of metals in water at both stations were in the descending order: Mn > Zn > Pb > Ni > Cu. However, the concentrations of metals in the soft body were in the descending order: Zn > Mn > Pb > Ni > Cu at both stations in all size groups of mussels tested. the concentration of zinc maintained a linear relationship with the size of the mussels, but manganese showed a reverse trend. Small size (4-5 cm) mussels accumulated more manganese (105.5 μg.g^?1 dry wt.) than larger ones (7-8 cm; 6.5 μg.g^?1 dry wt.). Both young and old is accumulate the same level of lead, copper and nickel in the soft body. the order of concentrations of metals (Mn, Pb, Zn, Ni and Cu) in the shell of mussels from both stations coincided with the order of concentrations of background water except for lead. the accumulation of lead was higher in shell (30.4-36.2 μg.g^?1 dry wt.) than in soft body (6.4-12.0 μg.g^?1 dry wt.). the pattern of concentration of metals in the various tissues reveal that the digestive glands have greater ability than other tissues to concentrate most metals under study. the concentration factors for soft body, shell and different tissues are presented. the advantages in using the common mussel for biomonitoring of contaminants in water is also discussed.     

Some aspects of the thermal tolerance of Trichomya hirsuta (Mollusca: Bivalvia) of Eastern Australia

The upper temperature tolerance range for Trichomya hirsuta L. is described for acclimation temperatures of 10° to 32°C at 30% S. Changes in thermal resistance with time are described along with the incipient lethal temperatures. The eurythermicity for the species is 240.7 C°-squared. The ultimate upper incipient lethal temperature is 35.1°C. Definition of the incipient sublethal temperature is given, and is equal to 32°C. Diet effects are shown not to be significant in short-term lethal experiments, but indicate that unfed mussels reduce their resistance after prolonged exposure to high temperatures. Size was also shown to have no effect on resistance and tolerance. A comparison of the tolerance triangle of T. hirsuta with those of the temperate species Mytilus edulis and Mya arenaria revealed that the 24-h LT₅₀ minus 2.2 C° approximates the incipient lethal temperature. The eurythermicities of the temperate species are Mytilus edulis, 363 C°-squared; and Mya arenaria, 415 C°-squared.     

Measurement of the adenylate energy charge in Nereis diversicolor and Nephtys sp. (Polychaeta: Annelida):

ATP-content and adenylate energy charge (AEC) ratios were determined in two polychaete species (Neries diversicolor and Nephytys sp.), sampled in ten stations along the heavily polluted Western Scheldt estuary (N. Belgium, S. Holland). The samples were taken between 27 December 1982 and 6 January 1983. Nereis diversicolor was also sampled in an unpolluted brackish water pond, and subjected to artificial stress by drying the organisms on filter paper. Adenine nucleotide levels were determined using the firefly bioluminescence reaction. The light emission was measured with the integration mode. As the Constant Light Signal reagent used contained AMP and probably ADP itself, both myokinase and pyruvatekinase had to be inactivated before the assay. The use of pepsin in acidic conditions to denaturate these enzymes is discussed. For both N. diversicolor and Nephtys sp., a significant relation between ATP-content and fresh weight is found in most samples. Within each species, ATP-content per g fresh weight is dependent on the sampling method, but it is not significantly different between stations. It is higher in Nephtys sp. from the W. Scheldt (130. 8 10^-5 g ATP/g fresh weight) than in N. diversicolor from the Dievengat (83.9 10^-5 g ATP/g fresh weight). This value in turn is significantly higher than that for N. diversicolor in the W. Scheldt (64.0 10^-5 g ATP/g fresh weight). In the drying experiment, AEC gradually decreases with increasing drying time. In the field, AEC is generally high and not significantly different between the three populations. AEC ratios also do not differ between stations within each population. It is argued that field monitoring of AEC in invertebrates is not valuable as a pollution assessment tool for two reasons. In polluted stations, only pollutant-resistant species will be found, and there is evidence that the maintenance of a stable population is impossible when the individuals constantly have low AECs.