Bivalve Molluscs Research Articles

Heavy metals accumulation in bivalve mollusks collected from coastal areas of southeast China

The distribution of six heavy metal and metalloids (As, Cd, Cr, Hg, Ni and Pb) was analyzed in 597 bivalve mollusks (8 species) collected from coastal areas of southeast China. Target hazard quotient, total hazard index, and target cancer risk were calculated to evaluate potential human health risks from bivalve consumption. The mean concentrations of As, Cd, Cr, Hg, Ni and Pb were 1.83, 0.581, 0.111, 0.0117, 0.268 and 0.137 mg kg−1 wet weight in bivalves. The average estimated daily intakes for As, Cd, Cr, Hg, Ni and Pb were 1.156, 0.367, 0.07, 0.007, 0.167 and 0.087 μg kg−1 body weight/day. Health risk assessment showed that there was no non-carcinogenic health risk to general residents to these metals from consumption of bivalves. Cd intake through mollusks posed a potential cancer risk. Accordingly, regular monitoring for heavy metals, especially Cd is recommended with respect to potential contaminant on marine ecosystems.

The story of Dreissena polymorpha (Pallas, 1771) (Mollusca Bivalvia) in Europe and Italy and observations on the origin of these populations

The story of Dreissena polymorpha (Pallas, 1771) (Mollusca Bivalvia) in Europe and Italy and observations on the origin of these populations

THE LEVEL OF NONSPECIFIC IMMUNE COMPLEXES AND OXIDATIVE PROCESSES IN THE TISSUES OF BIVALVE MOLLUSKS-INVADERS OF THE GORKY RESERVOIR

The content of nonspecific immune complexes and the intensity of oxidative processes in the tissues of invasive bivalve molluscs Dreissena polymorpha , D. bugensis , and Corbicula fluminea of the Gorky Reservoir were studied. Comparative analysis revealed differences in the quantitative parameters of immune complexes and malondialdehyde between C. fluminea and Dreissenidae. The identified interspecies differences seem to be associated both with the distinctive features of the lifestyle and morphological and physiological parameters, and with the adaptive capabilities of the body associated with the efficiency of the immune and antioxidant systems.

Anomaly Detection in Biological Early Warning Systems Using Unsupervised Machine Learning

The use of bivalve mollusks as bioindicators in automated monitoring systems can provide real-time detection of emergency situations associated with the pollution of aquatic environments. The behavioral reactions of Unio pictorum (Linnaeus, 1758) were employed in the development of a comprehensive automated monitoring system for aquatic environments by the authors. The study used experimental data obtained by an automated system from the Chernaya River in the Sevastopol region of the Crimean Peninsula. Four traditional unsupervised machine learning techniques were implemented to detect emergency signals in the activity of bivalves: elliptic envelope, isolation forest (iForest), one-class support vector machine (SVM), and local outlier factor (LOF). The results showed that the use of the elliptic envelope, iForest, and LOF methods with proper hyperparameter tuning can detect anomalies in mollusk activity data without false alarms, with an F1 score of 1. A comparison of anomaly detection times revealed that the iForest method is the most efficient. These findings demonstrate the potential of using bivalve mollusks as bioindicators in automated monitoring systems for the early detection of pollution in aquatic environments.

Effect of the Concentration of Cations (Ca2+, Mg2+, Na+, and K+) in Water on the Level of Oxidative Processes in the Tissues of Bivalves of the Family Dreissenidae

The results of studying the influence of the content of Ca2+, Mg2+, Na+, and K+ cations in water on the level of lipid peroxidation products and antioxidants in the tissues of bivalve mollusks, D. bugensis and D. polymorpha, are presented. Mollusks were caught in four water areas of the Gorky Reservoir, which differ in the concentrations of Ca2+, Mg2+, Na+, and K+ cations. A correlation relationship has been established between the quantitative parameters of cations in water and the intensity of peroxide processes, on the one hand, and the level of general antioxidant activity in mollusk tissues, on the other. Statistically significant interspecific differences in the studied parameters have been recorded in mollusks from areas with an increased concentration of cations.

Spatiotemporal analysis of the genetic and morphological variation of Iphigenia brasiliensis (Mollusca: Bivalvia) from the southwest tropical Atlantic

Iphigenia brasiliensis is a bivalve mollusk exploited as a shellfish and subsistence resource on the Brazilian coast, mainly in the north and northeast regions. Genetic (allozyme electrophoresis revealed eight gene loci) and morphological variations (multivariate morphometry of valves used 13 linear measurements of traditional and 19 Fourier coefficients of geometric morphometry) were studied, considering the geographic (445 km of the southwest tropical Atlantic), environmental (mangroves and channels of communication with the sea of three estuaries in the state of Rio de Janeiro), and temporal dimensions (over two years). I. brasiliensis showed high levels of genetic variation (the average number of alleles per locus ranged from 2.8 to 3.4, and the average heterozygosity ranged from 0.441 to 0.675). Bayesian analysis of population partitioning showed that the highest LnP(D) value was achieved for K = 3. These results indicated mixed ancestry, possibly oscillations in the dispersion dynamics among the different sampling groups, and temporal oscillations in the population sizes due to the anthropogenic influence on the studied estuaries. The results of morphological variation, inferred by the PERMANOVA from the Fourier analysis, indicated that a similar influence might occur in valves (also, the discriminant analysis showed that different groups could be consistently identified). In this sense, the studied populations may be organized in a dynamic of metapopulations. Finally, these are the first data on morphological and genetic variation of the species in the latitudinal, environmental, and temporal dimensions studied simultaneously, thus providing relevant information for the exploration, management, and conservation of this commercially important species.

Paleogeografické rozšírenie gaderského a ráztockého vápenca (vrchný pelsón – ilýr, hronikum, Západné Karpaty): rešerš

49 localities situated in preserved parts of the tectonic unit Hronicum were examined. The obtained data on the occurrence of brachiopods, bivalve molluscs, cephalopods, conodonts, holoturias and foraminifers in the sediments of the Upper Pelsonian – Illyrian (Jasenie, Schreyeralm, Gader, Ráztoka and unnamed crinoidal limestone) were projected into the paleogeographic scheme of the Hronicum. In the period after the disintegration of the Gutenstein platform, the Hronicum area was divided into a number of differentially synsedimentary subsiding parts. The submerged parts were the sedimentation space of the mentioned types of limestones. Non-submerged parts – carbonate platforms were a source of organodetritus for subsiding areas and a sedimentation area for the Gader Limestone.

Dynamics of fecal coliform bacteria along Canada's coast

The vast coastline provides Canada with a flourishing seafood industry including bivalve shellfish production. To sustain a healthy bivalve molluscan shellfish production, the Canadian Shellfish Sanitation Program was established to monitor the health of shellfish harvesting habitats, and fecal coliform bacteria data have been collected at nearly 15,000 marine sample sites across six coastal provinces in Canada since 1979. We applied Functional Principal Component Analysis and subsequent correlation analyses to find annual variation patterns of bacteria levels at sites in each province. The overall magnitude and the seasonality of fecal contamination were modelled by functional principal component one and two, respectively. The amplitude was related to human and warm-blooded animal activities; the seasonality was strongly correlated with river discharge driven by precipitation and snow melt in British Columbia, but such correlation in provinces along the Atlantic coast could not be properly evaluated due to lack of data during winter.

Ocean acidification stunts molluscan growth at CO2 seeps

Ocean acidification can severely affect bivalve molluscs, especially their shell calcification. Assessing the fate of this vulnerable group in a rapidly acidifying ocean is therefore a pressing challenge. Volcanic CO2 seeps are natural analogues of future ocean conditions that offer unique insights into the scope of marine bivalves to cope with acidification. Here, we used a 2-month reciprocal transplantation of the coastal mussel Septifer bilocularis collected from reference and elevated pCO2 habitats to explore how they calcify and grow at CO2 seeps on the Pacific coast of Japan. We found significant decreases in condition index (an indication of tissue energy reserves) and shell growth of mussels living under elevated pCO2 conditions. These negative responses in their physiological performance under acidified conditions were closely associated with changes in their food sources (shown by changes to the soft tissue δ13C and δ15N ratios) and changes in their calcifying fluid carbonate chemistry (based on shell carbonate isotopic and elemental signatures). The reduced shell growth rate during the transplantation experiment was further supported by shell δ13C records along their incremental growth layers, as well as their smaller shell size despite being of comparable ontogenetic ages (5–7 years old, based on shell δ18O records). Taken together, these findings demonstrate how ocean acidification at CO2 seeps affects mussel growth and reveal that lowered shell growth helps them survive stressful conditions.

Biomonitoring by using Rapid-Read Pathogenic Bacteria Indicator in Sediments and Bivalve Mollusks: Southern Gulf of Thailand, a Mangrove Area Case Study

Pathogenic bacteria groups can be applied to be rapid bioindicator for environmental assessment. The objective of study was to monitor 5 groups of indicator and pathogenic bacteria (Escherichia coli/ total coliform, Salmonella spp., Vibrio spp., Bacillus spp. and Clostridium spp.) in surface water sediments collected before monsoon and after monsoon season from 6 areas located in a Thepha District, Songkhla province mangrove closed to Southern gulf of Thailand. Each collected area were selected in criteria of totally different in environment parameter and tide. The relative levels of total coliforms, and E. coli, were typically increased in rainy season (July) compared with winter and summer at most sites. In parallel, the highest number of Vibrio spp. was found in summer (April). The highest number of E. coli and Coliform were detected during rainy season at the estuary area with low oxygen dissolved, the average numbers were 6.6×103 and 3.8×105 CFU/g, respectively. Coliform number shows negative correlate with dissolved oxygen (r2 = 0.756, p < 0.05). In addition, total coliform, Bacillus spp. and Clostridium spp. were found in bivalve mollusks during rainy season but the total was not over standard. A very strong positive correlation was found between the temperature and the number of Vibrio spp. and Bacillus spp. The number presence of Vibrio spp. has a strong positive correlation with pH, the number of Bacillus spp. and number of Clostridium spp. In contrast, Vibrio spp. number was strongly negative correlated with water salinity (r2 = 0.632, p < 0.05). Salmonella species were detected only 2 area around shrimp farm in between December of a year-round. In this study area, there are no evidence that the number of Salmonella and Clostridium species founded related to changing of season. This is the first baseline data as an alternative guide concept for the determination of bacterial indicators. Pathogenic bacteria number can be applied to be a key factors for a rapid health assessment for villager around study area that related to EIA in the near future. HIGHLIGHTS The common problem in biomonitoring process in environment are limit of biological indicator and less data collected to establish relative between bioindicator and environmental parameters Key pathogenic bacteria groups were selected and analyzed conducted in order to find the rapid-read method for biomonitoring and assessment This is the first baseline data as an alternative guide concept for the determination of bacterial indicators. Pathogenic bacteria number can be applied to be a key factors for a rapid health assessment for villager around study area that related to EIA in the near future GRAPHICAL ABSTRACT

Live-Dead Shifts in Molluscan Functional Diversity in Coastal Alabama

Abiotic and biotic environmental factors shape species behavioral, physiological, and morphological traits. Shifts in the diversity of these functional traits therefore can serve as an indicator of spatial and temporal changes in environmental conditions. In recent centuries, the delivery of nutrients to coastal ecosystems has increased markedly through changing waste management and land-use practices. Nutrient enrichment has increased rates of primary productivity, resulting in greater organic accumulation on the seafloor and the development of hypoxic conditions in some areas, due to the aerobic decomposition of phytoplankton blooms. Anthropogenic eutrophication and associated hypoxia have been monitored annually in the northern Gulf of Mexico for over four decades, with an emphasis on areas surrounding the Mississippi River Delta. To further understand how anthropogenic eutrophication affects functional diversity in benthic marine communities, we collected live and dead assemblages of bivalve mollusks from surficial sediments at five stations along the -20 meters isobath in coastal Alabama. Bivalves were categorized into functional groups using information about their mobility, fixation, feeding type, substrate preference, and body size. Consistent with our hypotheses, preliminary results indicate a temporal shift from benthic communities dominated primarily by epifaunal and infaunal suspension-feeding species to communities characterized primarily by deposit feeders, many of which dwell on the seafloor surface. Ongoing analyses will help identify the functional traits that are most sensitive to these changing environmental conditions. Understanding functional diversity shifts in the recent past can provide insight into how anthropogenic eutrophication may further impact benthic marine ecosystems in the future.

Parasite Dynamics: One Pattern and Multiple Possible Causes

How is parasitism likely to respond to anthropogenic global change? Digenean trematode prevalence among bivalve mollusk hosts in multiple coastal environments has been linked to sea-level rise on centennial and millennial time scales. Previous efforts have ruled out the influence of changing diversity, community structure, taphonomy, and salinity (fossil-based proxy) on this pattern but, until recently, we have not been able to address the role of other abiotic environmental factors. Here we present the results of stable isotope analyses (δ18O and δ13C) of the shallow marine bivalve Chamelea gallina from the Holocene and modern northern Adriatic (Italy) and trace element analysis of the estuarine bivalves Potamocorbula amurensis and Corbicula formosana from the Holocene Pearl River (China) delta using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Generalized Linear Models (GLM) of 1,297 δ18O and δ13C analyses from 57 C. gallina valves derived from 11 modern death assemblages and four Holocene core samples reveal that elevated trematode prevalence is associated with relatively negative δ18O values, relatively positive δ13C values, and a high correlation between δ18O and δ13C values. We interpret this to mean that trematode prevalence is higher during warm temperatures with minimal freshwater influence. GLMs of 3,295 LA-ICP-MS spot analyses on 48 valves from the two estuarine species (a separate GLM for each taxon), derived from 12 cored samples from Pearl River deposits, reveal a strong association between trematode prevalence and elevated Ba/Ca ratios and low species richness, which we interpret as high parasitic infestation of an oligotypic community in hypoxia-dominated environments. Taken together, the results suggest that parasitic patterns are linked to sea-level rise and geochemical insights point toward case-specific causal factors that are going to be more widespread due to anthropogenic climate change.

Impacts of Ocean Deoxygenation on Marine Benthos in the Gulf of Mexico

Ocean deoxygenation is a growing concern globally. Oxygen is less soluble in warm water, and warming temperatures also result in the slowdown of ocean circulation which limits oxygen delivery to deeper waters. Anthropogenic eutrophication has also contributed to the development of hypoxic conditions in many coastal areas. Here we investigate biodiversity structure along an environmental gradient in the Gulf of Mexico to see how patterns of spatiotemporal turnover can inform future biotic response of benthos to ocean deoxygenation. Live and dead assemblages of bivalve mollusks were collected at 15 stations offshore Louisiana, Alabama, and Florida. Abundance and body size data were collected, and specimens were classified functionally using information about feeding, attachment, life position, and body size. Environmental conditions were characterized using multi-decadal mean sea surface temperature (SST), dissolved oxygen (DO), and net primary productivity (NPP), and grain size data from our field samples. Stations in the north-central Gulf affected by Mississippi River discharge are characterized by higher NPP, lower DO, and higher percentages of silt and clay than stations in the northeastern Gulf. Both taxonomic and functional diversity significantly covary with this environmental gradient, with the lowest diversities observed at stations in the core of Louisiana’s “dead zone.” Analyses of spatiotemporal turnover patterns reveal shifts in the dominant feeding mode, with hypoxic environments containing a greater abundance of deposit and mixed feeders, compared with more oxygenated environments that host an abundance of suspension feeders and are characterized by a greater variety of feeding ecologies. Live-dead analyses reveal a shift in taxonomic and functional diversity in coastal Louisiana, that appears to coincide with the onset of anthropogenic eutrophication in these coastal settings.

Transcriptomic analysis provides molecular insights into immune response of Ruditapes philippinarum under Vibrio parahaemolyticus challenge

Ruditapes philippinarum is one of the most commercially important bivalve shellfish. However, the clam aquaculture industry has faced a great challenge due to Vibrio parahaemolyticus in recent years. In this study, we performed RNA-seq to profile the transcriptome of hepatopancreas tissue in the R. philippinarum with resistant individuals (survival group, VpS) and susceptible individuals (moribund group, VpM) after V. parahaemolyticus infection. A total of 1082 and 1876 differentially expressed genes were identified in the VpS group and VpM group after infection, respectively. The KEGG analysis reveal that immune related functional genes were significantly enriched in AMPK (5’-AMP-activated protein kinase), mTOR (mammalian target of rapamycin) signaling pathway, Autophagy and Lysosome, and phagosome in the hepatopancreas of Manila clams under V. parahaemolyticus challenge. For the RNA-seq validation, we verified 14 immune related DEGs by real-time quantitative PCR (qPCR). In addition, histological observation of hepatopancreas from Manila clam after V. parahemolyticus challenge was conducted and inflammatory response in tissues were appeared from the pathological morphology. The results obtained in this work provide valuable insights into the immune function of R. philippinarum under V. parahaemolyticus challenge.

D-amino acid peptides as antimicrobial agents against vibrio-associated diseases in aquaculture

Vibriosis is one of the most usual infection diseases in bivalve mollusks, particularly affecting seeds and larvae, which are more susceptible than adults to these bacterial infections. The devastating effect of vibriosis in shellfish hatcheries is aggravated by the increasing resistance of many Vibrio species to traditional antibiotics, highlighting the need to find new antimicrobial agents. Antimicrobial peptides (AMPs) are a promising alternative, however, their low stability can be a handicap for their practical application. In this study, the 3D structure and the stability of a synthetic all-D-amino acid peptide (D-Caerin) to proteases and extreme pH conditions have been analyzed and compared with its corresponding natural L-enantiomer peptide, Caerin 1.1. Moreover, the antimicrobial activity of D-Caerin has been tested in vitro against the control bacteria Micrococcus luteus CECT 245; and four Vibrio species: Vibrio aestuarianus CECT 625 T, Vibrio anguillarum CECT 522 T, Vibrio harveyi CECT 525 T and Vibrio tapetis CECT 4600 T, which are among the most representative causative agents of vibriosis in aquaculture. Our results demonstrate that D-Caerin contains two left-handed alpha helices, and is more stable and effective against the bacterial species tested than its corresponding natural L- counterpart. The bioactivity of D-Caerin has also been tested in vivo, in clam seeds infected with a mixed inoculum of these vibrio species. These preliminary assays show that D-Caerin-treated specimens exhibit higher survival rates after infection, demonstrating the superior stability of D-Caerin and its effectiveness against vibriosis-causative agents.

The Prevalence of Bacteria Commonly Related to the Production of Mussels and Oysters in Saldanha Bay

Bivalve molluscs are a good source of high quality protein and perform important ecological functions. Their ability to bioaccumulate materials in their soft tissues makes them suitable aquatic species for biomonitoring of environmental conditions. The discharge of treated and untreated sewage into the bivalve-growing areas is a concern. The aim of this study was to investigate the prevalence of bacterial microbiota in shellfish farms in Saldanha Bay harbour using pathogens commonly associated with shellfish-related foodborne disease outbreaks. Seawater and mussel samples were collected from five sampling points located in three sampling locations. Oyster samples were collected from the harbour deck immediately after harvesting by the farmers. The most probable number (MPN) method was used to enumerate E. coli and faecal coliforms. Cultural methods were used for the detection of Salmonella and Vibrio spp. The E. coli concentrations for 15 March and 14 July are <0.18 MPN/100 ml at all sampling sites and for 25 August, <0.18 MPN/100 ml for all sampling sites except sampling site SP2 (0.2 MPN/100 ml). Spikes were observed on the total MPN counts in winter. Salmonella and Vibrio spp. were not detected. However, other bacterial species were identified through their phenotypic profile using the VITEK 2 system. Based on the low E. coli-MPN concentrations, the study concluded that the molluscs were safe for human consumption. Further studies need to be conducted on the bacterial species identified.

Systematic Survey of Vibrio spp. and Salmonella spp. in Bivalve Shellfish in Apulia Region (Italy): Prevalence and Antimicrobial Resistance

The emergence of antimicrobial resistance (AMR) is increasingly common across the globe and aquatic ecosystems could be considered a reservoir of antibiotic-resistant bacteria. This study aimed to determine prevalence and antibiotic susceptibility of the potential pathogenic bacteria Salmonella spp. and Vibrio spp. in bivalve molluscs intended for human consumption, collected over a period of 19 months along the northern coast of Apulia region. The AMR profile was also determined in non-pathogenic Vibrio species, common natural inhabitants of seawater and a useful indicator for the surveillance of AMR in the environment. The current study presents data on the AMR of 5 Salmonella and 126 Vibrio isolates by broth microdilution MIC. Multidrug resistance (MDR) was observed in one S. Typhimurium strain towards sulfamethoxazole, trimethoprim, tetracycline, gentamicin, and ampicillin and in 41.3% of the Vibrio strains, mostly towards sulphonamides, penicillin, and cephems. All Vibrio isolates were sensitive to azithromycin, chloramphenicol, tetracycline, amoxicillin/clavulanic acid, gentamicin, streptomycin, amikacin, and levofloxacin. The AMR phenomenon in the investigated area is not highly worrying but not entirely negligible; therefore, in-depth continuous monitoring is suggested. Results concerning the antibiotic agents without available specific clinical breakpoints could be useful to upgrade the MIC distribution for Vibrio spp. but, also, the establishment of interpretative criteria for environmental species is necessary to obtain a more complete view of this issue.

Gamma-aminobutyric acid (GABA) suppresses hemocyte phagocytosis by binding to GABA receptors and modulating corresponding downstream pathways in blood clam, Tegillarca granosa

Although accumulating data demonstrated that gamma-aminobutyric acid (GABA), an inhibitory neurotransmitter, plays an important regulatory role in immunity of vertebrates, its immunomodulatory function and mechanisms of action remain poorly understood in invertebrates such as bivalve mollusks. In this study, the effect of GABA on phagocytic activity of hemocytes was evaluated in a commercial bivalve species, Tegillarca granosa. Furthermore, the potential regulatory mechanism underpinning was investigated by assessing potential downstream targets. Data obtained demonstrated that in vitro GABA incubation significantly constrained the phagocytic activity of hemocytes. In addition, the GABA-induced suppression of phagocytosis was markedly relieved by blocking of GABAA and GABAB receptors using corresponding antagonists. Hemocytes incubated with lipopolysaccharides (LPS) and GABA had significant higher K+-Cl- cotransporter 2 (KCC2) content compared to the control. In addition, GABA treatment led to an elevation in intracellular Cl−, which was shown to be leveled down to normal by blocking the ionotropic GABAA receptor. Treatment with GABAA receptor antagonist also rescued the suppression of GABAA receptor-associated protein (GABARAP), KCC, TNF receptor associated factor 6 (TRAF6), inhibitor of nuclear factor kappa-B kinase subunit alpha (IKKα), and nuclear factor kappa B subunit 1 (NFκB) caused by GABA incubation. Furthermore, incubation of hemocytes with GABA resulted in a decrease in cAMP content, an increase in intracellular Ca2+, and downregulation of cAMP-dependent protein kinase (PKA), calmodulin kinase II (CAMK2), calmodulin (CaM), calcineurin (CaN), TRAF6, IKKα, and NFκB. All these above-mentioned changes were found to be evidently relieved by blocking the metabotropic G-protein-coupled GABAB receptor. Our results suggest GABA may play an inhibitory role on phagocytosis through binding to both GABAA and GABAB receptors, and subsequently regulating corresponding downstream pathways in bivalve invertebrates.

Shellfish as Biosensors in Online Monitoring of Aquatic Ecosystems: A Review of Russian Studies

The use of biological objects in monitoring the state of the environment and the changes caused by the impact of environmental pollution on marine and fresh waters is a promising tool due to a lower cost in comparison to traditional monitoring and the ability to receive immediate information about the ecosystem status. In this review, we summarize the biological information about shellfish biomonitors and the results of studies focused on the development and use of the bioindicator species in early warning systems in Russia. Since the mid-1980s, Russian specialists have developed online biomonitoring systems; as in the rest of world, there are two main approaches that are currently applied to study the physiological status of potential biosensor shellfish species and to monitor freshwater and marine systems: valvometry (registration of gaping activity in bivalve mollusks) and photoplethysmography (registration of cardiac activity in mollusks and crustaceans). Valve movement responses to stressors such as abnormal conditions and pollutants include the closure of shell valves for a long period, decrease in the average distance between valves, rapid shell opening, and higher closing frequency. Cardiac activity reactions of shellfish to stress factors include rapid increases in heart rate and stress index, higher variability in heart rate than under normal conditions, and longer periods required for heart rate recovery after stress. The most common bioindicators used to monitor environmental disturbances in marine ecosystems are blue mussels, Iceland scallops, and red king crabs in cold-water habitats and Black Sea mussels in warmer waters as well as freshwater mussels and crayfish in fresh waters.

Convergence and contingency in the evolution of a specialized mode of life: multiple origins and high disparity of rock-boring bivalves.

Evolutionary adaptation to novel, specialized modes of life is often associated with a close mapping of form to the new function, resulting in narrow morphological disparity. For bivalve molluscs, endolithy (rock-boring) has biomechanical requirements thought to diverge strongly from those of ancestral functions. However, endolithy in bivalves has originated at least eight times. Three-dimensional morphometric data representing 75 species from approximately 94% of extant endolithic genera and families, along with 310 non-endolithic species in those families, show that endolithy is evolutionarily accessible from many different morphological starting points. Although some endoliths appear to converge on certain shell morphologies, the range of endolith shell form is as broad as that belonging to any other bivalve substrate use. Nevertheless, endolithy is a taxon-poor function in Bivalvia today. This limited richness does not derive from origination within source clades having significantly low origination or high extinction rates, and today's endoliths are not confined to low-diversity biogeographic regions. Instead, endolithy may be limited by habitat availability. Both determinism (as reflected by convergence among distantly related taxa) and contingency (as reflected by the endoliths that remain close to the disparate morphologies of their source clades) underlie the occupation of endolith morphospace.