Marine Bivalve Mytilus Edulis Research Articles

Heavy Metal Determination of Bivalves in Cagayan Valley, Philippines

Level of heavy metals like Cadmium (Cd) and Lead (Pb) in bivalves has been intensively studied during recent years as these hazardous substances could be accumulated in the biota and has been a hot issue in marine environmental studies. By consuming the shellfish, risk of bivalve related diseases may increase. And this shellfish poisoning is a concern to public health. This research study aims to determine if the Bivalves in Cagayan Valley, Philippines is safe to consume. The Freshwater clam (Corbicula fluminea) and the Marine mussel (Mytilus edulis) in Cagayan Valley, Philippines was collected for this study. The byssus and shells were removed, leaving only soft tissues to be used for the analysis and they were categorized into two. Graphite Furnace- Atomic Absorption Spectrophotometer (GFAAS) was used to determine the concentrations of Cadmium (Cd) and Lead (Pb). The results showed that the Freshwater bivalves Corbicula fluminea has a concentration 0.006 μg/g of Lead (Pb) and a concentration 0.016 μg/g. of Cadmium (Cd) while for Marine bivalves Mytilus edulis, the concentration of Pb was 0.011 μg/g and the concentration of Cd levels was 0.015 μg/g. The test results showed that the heavy metals, lead, and cadmium, were at low levels when referred to guidelines on heavy metals for food safety by different countries, particularly Malaysia. Thus, the results that were found were quite lower and there are no health risks to the people when consuming these bivalves collected from the province of Cagayan. Based on the results of the study conducted, the researchers recommend using different bivalve species to know the levels of heavy metals on bivalve species, investigate lead and cadmium heavy metals concentrations of one species collected in different areas/locations in Cagayan Valley and investigate the lead and cadmium heavy metal concentration of different bivalves in a regular basis i.e., monthly, or quarterly for at least 1 year.

Biomarker-based assessment of sublethal toxicity of organic UV filters (ensulizole and octocrylene) in a sentinel marine bivalve Mytilus edulis

The global occurrence of organic UV filters in the marine environment is of increasing ecotoxicological concern. Here we assessed the toxicity of UV filters ensulizole and octocrylene in the blue mussels Mytilus edulis exposed to 10 or 100 μg l−1 of octocrylene and ensulizole for two weeks. An integrated battery of biochemical and molecular biomarkers related to xenobiotics metabolism and cellular toxicity (including oxidative stress, DNA damage, apoptosis, autophagy and inflammation) was used to assess the toxicity of these UV filters in the mussels. Octocrylene (but not ensulizole) accumulated in the mussel tissues during the waterborne exposures. Both studied UV filters induced sublethal toxic effects in M. edulis at the investigated concentrations. These effects involved induction of oxidative stress, genotoxicity (indicated by upregulation of DNA damage sensing and repair markers), upregulation of apoptosis and inflammation, and dysregulation of the xenobiotic biotransformation system. Octocrylene induced cellular stress in a concentration-dependent manner, whereas ensulizole appeared to be more toxic at the lower (10 μg l−1) studied concentration than at 100 μg l−1. The different concentration-dependence of sublethal effects and distinct toxicological profiles of ensulizole and octocrylene show that the environmental toxicity is not directly related to lipophilicity and bioaccumulation potential of these UV filters and demonstrate the importance of using bioassays for toxicity assessment of emerging pollutants in coastal marine ecosystems.

Effects of hypoxia and reoxygenation on intermediary metabolite homeostasis of marine bivalves Mytilus edulis and Crassostrea gigas

Marine benthic invertebrates are frequently exposed to fluctuating oxygen levels resulting in hypoxia-reoxygenation (H/R) stress in the intertidal, estuarine and shallow coastal habitats. H/R stress can strongly affect the organisms' physiological performance due to the negative shifts in bioenergetics and redox balance. H/R stress commonly leads to the depletion of energy substrates and accumulation of anaerobic end products, but the effects of H/R stress on the homeostasis of the intermediate nitrogenous compounds are not well understood. We studied the effects of the short-term and long-term hypoxia (1 and 6 days, respectively) and subsequent reoxygenation on the metabolite profiles of free amino acids (FAAs), as well as the intermediates of the urea cycle and purine metabolism in two species of hypoxia-tolerant intertidal bivalves, the blue mussels Mytilus edulis and the Pacific oysters Crassostrea gigas. Accumulation of succinate was assessed to determine the role of anaerobiosis in the metabolic responses to H/R stress. Our study showed that the more hypoxia-tolerant of the two studied species (C. gigas) had lower rate of succinate accumulation during hypoxia (indicating stronger metabolic rate suppression) and was better able to maintain the homeostasis of nitrogenous intermediates during H/R stress compared with the less hypoxia-tolerant M. edulis. Furthermore, analysis of the metabolite profiles indicate that the oysters maintain high levels of cytoprotective compounds (such as taurine and GABA), accumulate lower levels of potential prooxidants (such as succinate and hypoxanthine) and experience less damage to oxidation-prone thiol-containing amino acids such as cysteine, homocysteine and methionine during hypoxia and reoxygenation compared with the blue mussels. This study indicates a potentially important role of intermediate metabolite homeostasis in the tolerance to prolonged hypoxia and H/R stress in marine organisms and opens avenue for further testing of this hypothesis in a broader comparative framework.

Effects of intermittent hypoxia on cell survival and inflammatory responses in the intertidal marine bivalves Mytilus edulis and Crassostrea gigas.

Hypoxia is a major stressor in estuarine and coastal habitats, leading to adverse effects in aquatic organisms. Estuarine bivalves such as blue mussels (Mytilus edulis) and Pacific oysters (Crassostrea gigas) can survive periodic oxygen deficiency but the molecular mechanisms that underlie cellular injury during hypoxia-reoxygenation are not well understood. We examined the molecular markers of autophagy, apoptosis and inflammation during short-term (1 day) and long-term (6 days) hypoxia and post-hypoxic recovery (1 h) in mussels and oysters by measuring the lysosomal membrane stability, activity of a key autophagic enzyme (cathepsin D) and mRNA expression of the genes involved in the cellular survival and inflammation, including caspase 2, 3 and 8, Bcl-2, BAX, TGF-β-activated kinase 1 (TAK1), nuclear factor kappa B1 (NF-κB) and NF-κB activating kinases IKKα and TBK1. Crassostrea gigas exhibited higher hypoxia tolerance, as well as blunted or delayed inflammatory and apoptotic response to hypoxia and reoxygenation as shown by the later onset and/or the lack of transcriptional activation of caspases, BAX and the inflammatory effector NF-κB, compared with M. edulis Long-term hypoxia resulted in upregulation of Bcl-2 in the oysters and mussels, implying activation of anti-apoptotic mechanisms. Our findings indicate the potential importance of the cell survival pathways in hypoxia tolerance of marine bivalves, and demonstrate the utility of the molecular markers of apoptosis and autophagy for the assessment of sublethal hypoxic stress in bivalve populations.

The effects of ZnO nanostructures of different morphology on bioenergetics and stress response biomarkers of the blue mussels Mytilus edulis

Biofouling causes massive economical losses in the maritime sector creating an urgent need for effective and ecologically non-harmful antifouling materials. Zinc oxide (ZnO) nanorod coatings show promise as an antifouling material; however, the toxicity of ZnO nanorods to marine organisms is not known. We compared the toxicity of suspended ZnO nanorods (NR) with that of ZnO nanoparticles (NP) and ionic Zn2+ in a marine bivalve Mytilus edulis exposed for two weeks to 10 or 100 μg Zn L−1 of ZnO NPs, NRs or Zn2+, or to immobilized NRs. The multi-biomarker assessment included bioenergetics markers (tissue energy reserves, activity of mitochondrial electron transport system and autophagic enzymes), expression of apoptotic and inflammatory genes, and general stress biomarkers (oxidative lesions, lysosomal membrane stability and metallothionein expression). Exposure to ZnO NPs, NRs and Zn2+ caused accumulation of oxidative lesions in proteins and lipids, stimulated autophagy, and led to lysosomal membrane destabilization indicating toxicity. However, these responses were not specific for the form of Zn (NPs, NR or Zn2+) and showed no monotonous increase with increasing Zn concentrations in the experimental exposures. No major disturbance of the energy status was found in the mussels exposed to ZnO NPs, NRs, or Zn2+. Exposure to ZnO NPs and NRs led to a strong induction of apoptosis- and inflammation-related genes, which was not seen in Zn2+ exposures. Based on the integrated biomarker response, the overall toxicity as well as the pro-apoptotic and pro-inflammatory action was stronger in ZnO NPs compared with the NRs. Given the stability of ZnO NR coatings and the relatively low toxicity of suspended ZnO NR, ZnO NR coating might be considered a promising low-toxicity material for antifouling paints.

Effects of a common pharmaceutical, atorvastatin, on energy metabolism and detoxification mechanisms of a marine bivalve Mytilus edulis

Biologically active compounds from pharmaceuticals cause concern due to their common occurrence in water and sediments of urbanized coasts and potential threat to marine organisms. Atorvastatin (ATO), a globally prescribed drug, is environmentally stable and bioavailable to marine organisms; however, the physiological and toxic effects of this drug on ecologically important coastal species are yet to be elucidated. We studied the effect of ATO (˜1.2 μg L−1) on bioenergetics (including whole-organism and mitochondrial respiration, as well as tissue energy reserves and mRNA expression of genes involved in mitochondrial biogenesis and fatty acid metabolism in the gills and the digestive gland) of a keystone bivalve Mytulis edulis (the blue mussel) from the Baltic Sea. Xenobiotic detoxification systems including activity and mRNA expression of P-glycoprotein, and Phase I and II biotransformation enzymes (cytochrome P450 monooxygenase CYP1A and glutathione transferase, GST) were also assessed in the gill and digestive gland of the mussels. Exposure to ATO caused rapid uptake and biotransformation of the drug by the mussels. Standard metabolic rate of ATO-exposed mussels increased by 56% indicating higher maintenance costs, yet no changes were detected in the respiratory capacity of isolated mitochondria. ATO exposure led to ˜60% decrease in the lysosomal membrane stability of hemocytes and ˜3-fold decrease in the whole-organism P-glycoprotein-driven and diffusional efflux of xenobiotics indicating altered membrane properties. The digestive gland was a major target of ATO toxicity in the mussels. Exposure of mussels to ATO led to depletion of lipid, carbohydrate and protein pools, and suppressed transcription of key enzymes involved in mitochondrial biogenesis (peroxisome proliferator-activated receptor gamma coactivator 1-alpha PGC-1α) and fatty acid metabolism (acetyl-CoA carboxylase and CYP4Y1) in the digestive gland. No bioenergetic disturbances were observed in the gills of ATO-exposed mussels, and elevated GST activity indicated enhanced ATO detoxification in this tissue. These data demonstrate that ATO can act as a metabolic disruptor and chemosensitizer in keystone marine bivalves and warrant further investigations of statins as emerging pollutants of concern in coastal marine ecosystems.

Transcriptomic approach: A promising tool for rapid screening nanomaterial-mediated toxicity in the marine bivalve Mytilus edulis—Application to copper oxide nanoparticles

The extensive development of nanotechnologies will inevitably lead to the release of nanomaterials (NMs) in the environment. As the aquatic environments represent the ultimate sink for various contaminants, it is highly probable that they also constitute a reservoir for NMs and hence aquatic animals represent potential targets. In a regulatory perspective, it is necessary to develop tools to rapidly screen the impact of NMs on model organisms, given that the number of NMs on the market will be increasing. In this context High Throughput Screening approaches represent relevant tools for the investigation of NM-mediated toxicity. The objective of this work was to study the effects of copper oxide nanoparticles (CuONPs) in the marine bivalve Mytilus edulis, using a transcriptomic approach. Mussels were exposed in vivo to CuONPs (10 μg·L−1CuO NPs) for 24 h and analysis of mRNA expression levels of genes implicated in immune response, antioxidant activities, cell metabolism, cell transport and cytoskeleton was investigated by qPCR on hemocytes and gills. Results showed common effects of CuONPs and its ionic counterpart. However, greater effects of CuONPs on GST, SOD, MT, Actin, ATP synthase gene expressions were observed compared to ionic form indicating that toxicity of CuONPs is not solely due to the release of Cu2+. Even though M. edulis genome is not fully characterized, this study provides additional knowledge on the signaling pathways implicated in CuONP-mediated toxicity and demonstrates the reliability of using a qPCR approach to go further in the cellular aspects implicated in response to NPs in marine bivalves.

Effect of ultra-sonication and its use with sodium hypochlorite as antifouling method against Mytilus edulis larvae and mussel.

Biofouling is a stubborn problem in cooling systems where using raw water from lakes, rivers, and sea. The effect of ultrasound and its sequential application with sodium hypochlorite (chlorination) upon marine bivalve Mytilus edulis (blue mussel), a massive fouling organism, has been studied and discussed here. The results obtained from the work carried out have shown that 42kHz ultrasound is better than 28kHz in accordance with veliger larvae mortality. The 42kHz ultrasound has enhanced the mortality rate of veliger larvae than only free-residual chlorination up to 99%. On the other side, the 14-mm size mussel was less resistance than 25-mm size mussel to 42kHz ultrasonication, among the studied two sizes (14 and 25mm) of the blue mussel. Lethal time (100%) have decreased by 1-12% used for the sequential action of 42kHz ultrasonic followed by free-residual chlorination compare with only free-residual chlorination treatment. The obtained results are put forward that the application of ultra-sonication before chlorination can reduce the mussel extinct time up to 12%. Obviously, this result will provide a possible use of ultra-sonication with famous chlorination antifouling treatment and eventually can decrease the chlorine exposure time and dose. It could discharge low chlorine by-products that may provide an environment friendly way.

Sensitivity of the mussel Mytilus edulis to substrate‑borne vibration in relation to anthropogenically generated noise

© 2015 Inter-Research. Many anthropogenic activities in the oceans involve direct contact with the seabed (for example pile driving), creating radiating particle motion waves. However, the consequences of these waveforms to marine organisms are largely unknown and there is little information on the ability of invertebrates to detect vibration, or indeed the acoustic component of the signal. We quantified sensitivity of the marine bivalve Mytilus edulis to substrate-borne vibration by exposure to vibration under controlled conditions. Sinusoidal excitation by tonal signals at frequencies within the range 5 to 410 Hz was applied during the tests, using the 'staircase' method of threshold determination. Thresholds were related to mussel size and to seabed vibration data produced by anthropogenic activities. Clear behavioural changes were observed in response to the vibration stimulus. Thresholds ranged from 0.06 to 0.55 m s -2 (acceleration, root mean squared), with valve closure used as the behavioural indicator of reception and response. Thresholds were shown to be within the range of vibrations measured in the vicinity of anthropogenic operations such as pile driving and blasting. The responses show that vibration is likely to impact the overall fitness of both individuals and mussel beds of M. edulis due to disruption of natural valve periodicity, which may have ecosystem and commercial implications. The observed data provide a valuable first step to understanding the impacts of such vibration upon a key coastal and estuarine invertebrate which lives near industrial and construction activity, and illustrate that the role of seabed vibration should not be underestimated when assessing the impacts of noise pollution.

Immunotoxicity of heavy metals (silver, cadmium, mercury and lead) on marine bivalve Mytilus edulis: in vitro exposure of hemocytes

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Identification of Reproduction-Specific Genes Associated with Maturation and Estrogen Exposure in a Marine Bivalve Mytilus edulis

BackgroundWhile it is established that vertebrate-like steroids, particularly estrogens (estradiol, estrone) and androgens (testosterone), are present in various tissues of molluscs, it is still unclear what role these play in reproductive endocrinology in such organisms. This is despite the significant commercial shellfishery interest in several bivalve species and their decline.Methodology/Principal FindingsUsing suppression subtraction hybridisation of mussel gonad samples at two stages (early and mature) of gametogenesis and (in parallel) following controlled laboratory estrogen exposure, we isolate several differentially regulated genes including testis-specific kinases, vitelline lysin and envelope sequences.ConclusionsThe differentially expressed mRNAs isolated provide evidence that mussels may be impacted by exogenous estrogen exposure.

Oxygen consumption, ammonia excretion, and filtration rate of the marine bivalve Mytilus edulis exposed to methamidophos and omethoate

In this study, the oxygen consumption, ammonia excretion, and filtration rate were monitored in Mytilus edulis in response to administration of the two pesticides, methamidophos and omethoate. Five sublethal concentrations (1, 10, 50, 100, and 200 µgL−1) were administered over 96 h. Oxygen consumption rates increased following administration of all concentrations of methamidophos for 96 h and to the lower concentrations of omethoate (1, 10, and 50 µg L−1) from 6 to 24 h. Over 24 h, oxygen consumption decreased significantly. Ammonia excretion rates were higher than the control after 36 h of exposure to methamidophos, while reduction was observed when M. edulis was exposed to omethoate. The O:N ratios increased when the animals were first exposed to these two pesticides and then decreased at all the concentrations. At the concentrations of 100 and 200 µgL−1, the O:N ratio was below 30 after 72 h. The filtration rate of M. edulis decreased with the increasing concentration of pesticide exposure.

Effects of temperature on scope for growth and accumulation of Cd, Co, Cu and Pb by the marine bivalve Mytilus edulis

In many aquatic organisms including Mytilus edulis, the role of temperature on bioaccumulation of metals is still not clearly understood. In this study, uptake and accumulation of Cu, Co, Cd and Pb in mussels were investigated at different temperatures (6-26 degrees C). Results from exposure of isolated gills showed a positive relationship between temperature and metal uptake. But in whole organism experiments, only the accumulations of non-essential metals (Cd, Pb) showed a similar trend while the two essential metals Co and Cu were independent and inversely related to temperature, respectively. With exception of Cu, elimination process appeared to be independent of temperature. The study also showed that neither changes in scope for growth (SFG) of mussels nor chemical speciation could fully account for the observed temperature-effects. Overall, these results suggest that fundamentally (i.e. at epithelial membranes), temperature-effects on uptake are largely due to changes in solution chemistry and physical kinetics, which favours higher uptake at high temperature. But at whole organism level, complex physiological responses appears to mask the relationship, particularly for biologically essential metals like copper.

Influence of age and size on pumping activity and stress resistance in the marine bivalve Mytilus edulis L.

We studied age and size dependence of pumping and respiration rates, mortality during prolonged air exposure and the changes in behavioural response to cyclic salinity fluctuations combined with elevated temperatures in the White Sea blue mussels Mytilus edulis L. Five age groups (2–9 years) and three size groups: small (S, mean wet tissue mass 0.12 g), medium (M, mean wet tissue mass 0.39 g) and large (L, mean wet tissue mass 0.78 g) were analysed. Respiration rate was measured in closed respirometers. Pumping rate was determined by a laser beam to monitor the changes in water level when the inhalant and exhalant siphons were in separate compartments of the aquarium. To study their response to environmental stress, the mussels were subjected to cyclic salinity fluctuations at normal (10 °C) and elevated (20 °C) temperatures. Two parameters were noted: (1) the salinity at which shell valves either opened or closed at both temperatures, and (2) intra-individual variation of the behavioural response to salinity changes at both temperatures. Size and age affect physiological processes in the blue mussel. The responses of M. edulis to environmental stress including low salinity, elevated temperature and air exposure as well as respiration rate are generally size-dependent. Effects of age on sensitivity to low salinity and survival in air are minor. Pumping rates of mussels are significantly affected by both size and age of the animals. The disproportional decrease of pumping rate is observed at the age of about 7–8 years old.

Rapid assessment of organophosphorous/carbamate exposure in the bivalve mollusc Mytilus edulis using combined esterase activities as biomarkers

Carboxylesterases in bivalve molluscs exhibit greater sensitivity to organophosphorous and carbamate pesticides than acetylcholinesterase and are present at higher levels. The aim of the present study was to combine measurement of both acetylcholinesterase and carboxylesterase activities in the marine bivalve Mytilus edulis in order to detect the effects of pesticide exposure. Spectrophotometric assays in microtitreplate format were optimised for use with M. edulis haemolymph and tissue homogenate samples. This permitted the nature and distribution of the enzymes to be determined. One predominant pharmacological form of activity consistent in its patterns of activation and inhibition with acetylcholinesterase was identified in the haemolymph with an apparent K m for acetylthiocholineiodide of 1.33 mM. Carboxylesterase activity in the tissues was characterised by its preferential hydrolysis of the substrate analogue phenylthioacetate. Concentration-dependent inhibition of both activities was demonstrated following in vitro incubation with diisopropylfluorophosphate (DFP), paraoxon and eserine in the range 0.1–3.0 mM. When M. edulis ( n=10) were exposed for 24 h to concentrations of eserine or paraoxon of 0.05–1.0 mM, the percentage inhibition of acetylcholinesterase was in each case greater than for carboxylesterase and reached statistical significance at lower concentrations. In all exposures, a proportion of carboxylesterase activity was present which remained resistant to inhibition by either organophosphorous or carbamate compounds. The ecotoxicological significance of these findings for the environmental monitoring of pesticide exposure is discussed.

Oxidative-stress: comparison of species specific and tissue specific effects in the marine bivalves Mytilus edulis (L.) and Dosinia lupinus (L.)

This study describes a novel approach to the objective of identifying a suitable biomarker of oxidative-stress in marine animals and evaluates an established assay under controlled experimental conditions in vivo and in vitro. Live animals and tissue homogenates of the euryoxic blue mussel Mytilus edulis (L.), and the stenoxic smooth artemis Dosinia lupinus (L.), were exposed to oxidative-stress generated using a 60Co γ-radiation source. In live organisms, mortality-rates were significantly different between species. M. edulis showed zero mortality and D. lupinus 30% mortality over 18 h. Protein-carbonyl (PCO) content was determined by colourimetric assay (total protein-carbonyl) or immunodetection (for individual proteins) in four tissue types: digestive gland, mantle, adductor muscle and foot. In tissue homogenates, digestive gland and adductor muscle of both species showed significant increases (greater for D. lupinus) in PCO content following irradiation in vitro. All tissues from live animals (with the exception of M. edulis mantle and adductor muscle of D. lupinus which died under irradiation) showed significantly different levels of PCOs following irradiation; D. lupinus PCO levels were increased whilst in M. edulis PCO content decreased. In D. lupinus which died during irradiation, PCO content was greater than in those D. lupinus which survived, particularly in the adductor muscle, the former were inceased by 74% above controls. The findings support the hypothesis that species-specific adaptations to euryoxic and stenoxic environments, and metabolic requirements of different tissues, should result in differing ROS defences.

Uptake of heavy metals in isolated gills of the marine bivalve Mytilus edulis

Uptake of heavy metals in isolated gills of the marine bivalve Mytilus edulis

Extracellular Ca2+ entry and Ca2+ release from inositol 1,4,5-trisphosphate-sensitive stores function at fertilization in oocytes of the marine bivalve Mytilus edulis.

An oocyte of the marine bivalve Mytilus edulis, which is arrested at metaphase I, reinitiates meiosis at fertilization. The fertilized oocyte shows increases in intracellular Ca2+ ([Ca2+]i) comprising three different phases: an initial large [Ca2+]i transient, a subsequent low but sustained [Ca2+]i elevation, and repetitive small [Ca2+]i transients. In this study, we have investigated the sources and mechanisms of the sperm-induced [Ca2+]i increases. Application of methoxyverapamil (D-600), an inhibitor of voltage-dependent Ca2+ influx, suppressed the initial [Ca2+]i transient but did not affect the following two phases of [Ca2+]i changes. Injection of heparin, an antagonist of the inositol 1,4,5-trisphosphate (IP3) receptor, inhibited the later two phases without much affecting the initial transient. Combined application of D-600 and heparin almost completely abolished the three phases of the sperm-induced [Ca2+]i changes. Furthermore, Ca2+ influx caused by seawater containing excess K+ was blocked by D-600 but not by heparin, and IP3-induced Ca2+ release caused by photolysis of injected 'caged' derivatives of IP3 was blocked by heparin but not by D-600. These results strongly suggest that two types of Ca2+ mobilization systems, the extracellular Ca2+ entry responsible for an initial [Ca2+]i transient and the IP3 receptor-mediated Ca2+ release responsible for the following two phases of [Ca2+]i changes, function at fertilization of Mytilus oocytes.

Developmental stability is not disrupted by extensive hybridization and introgression among populations of the marine bivalve molluscs Mytilus edulis (L.) and M. galloprovincialis (Lmk.) from south-west England

Developmental stability is not disrupted by extensive hybridization and introgression among populations of the marine bivalve molluscs Mytilus edulis (L.) and M. galloprovincialis (Lmk.) from south-west England

A neuroimmunoregulatory-like mechanism responding to stress in the marine bivalve Mytilus edulis

Mytilus edulis has been the subject of recent studies to determine whether the relationship between the immune and nervous systems seen in vertebrates also exists in invertebrates. In the present study the effects of experimentally induced “stressful” stimuli on immunoactive hemocytes were studied in this mollusc. This subpopulation of invertebrate blood cells, resembling vertebrate granulocytes, has been previously shown to produce and react to opioid peptides. Their activation, like that of vertebrate immunocytes, expresses itself in distinctive conformational changes preceding cellular mobilization. The cellular response to “stress” observed is the same as that to the administration of exogenous mammalian opioid peptides. This strongly suggests that under the conditions of stressful stimuli, the immune/defense system can be alerted by endogenous neuropeptides. The involvement of opioids in neuroimmunoregulatory phenomena appears to have a long evolutionary history.