Effects of Environmental Factors on Byssal Thread Formation in Some Members of the Family Mytilidae from the Sea of Japan

The ability to attach repeatedly to a substrate (glass, boulders, sand) in three common mussel species of the upper sublittoral zone of the Sea of Japan, Grayan's mussel Crenomytilus grayanus, the Korean mussel Mytilus coruscus, and northern horse mussel Modiolus modiolus, was studied under experimental conditions. It was found that during 120 h of the experiment C. grayanus and M. modiolus produced more byssal threads than M. coruscus. A decrease in the water temperature from 20 to 0°C slowed the rate of production of byssal threads down to full passivity in some experimental mollusks. This was more typical of M. coruscus and less typical of C. grayanus. Renewed threads differed in their length, thick, size of the adhesive plate, and strength. M. coruscus formed the shortest, thickest, and strongest threads with rather a large adhesive disk. The observed differences are discussed from the position of morphophysiological adaptations of species for colonization of different natural substrata under contrasting conditions of the upper sublittoral zone.     

Sperm Ultrastructure of Two Mollusk Species Geukensia demissa and Modiolus modiolus (Mytilidae, Bivalvia)

Sperm ultrastructure was studied in two Atlantic species of bivalve mollusks Geukensia demissa and Modiolus modiolus (Mytilidae). These spermatozoa have a classic structure common for species with external fertilization: the head of the spermatozoon of G. demissa and M. modiolus consists of an acrosome, including an acrosomal vesicle and periacrosomal material, a nucleus, and a middle part with two mutually perpendicular centrioles, surrounded by a ring of spherical mitochondria. The spermatozoa of G. demissa and M. modiolus differ in the general shape and size of the head (M. modiolus, 5.8 × 4 m; G. demissa, 4.2 × 2.5 m), as well as the structure of the acrosome and the number of mitochondria (M. modiolus, 8–12; G. demissa, 5–6). The spermatozoa of the Atlantic species M. modiolus and M. modiolus (M. kurilensis) from the Sea of Japan are close in ultrastructure, but differ in the number of mitochondria. This could possibly be a reason to consider M. modiolus from the Sea of Japan as a separate subspecies, M. modiolus kurilensis. In ultrastructure, the spermatozoa of G. demissa differ significantly from the spermatozoa of M. modiolus, but are similar to the spermatozoa of species of the genus Brachidontes.     

Purification of a novel nitric oxide inhibitory peptide derived from enzymatic hydrolysates of Mytilus coruscus

Shellfish contain significant levels of high quality protein and are therefore a potential source for biofunctional high-value peptides. To purify a novel anti-inflammatory peptide from Mytilus coruscus (M. coruscus), we applied enzymatic hydrolysis and tangential flow filtration (TFF) and investigated its nitric oxide inhibitory property. To prepare the peptide, eight proteases were employed for enzymatic hydrolysis. Flavouzyme hydrolysates, which showed clearly superior nitric oxide inhibitory activity on lipopolysaccharide (LPS)-stimulated RAW264.7, were further purified using a TFF system and consecutive chromatographic methods. Finally, a novel anti-inflammatory peptide composed of 10 amino acid residues was obtained, and the sequence was identified as Gly-Val-Ser-Leu-Leu-Gln-Gln-Phe-Phe-Leu at N-terminal position. The peptide from M. coruscus effectively inhibited nitric oxide production on macrophage cells. This is the first report of an anti-inflammatory peptide derived from the hydrolysates of M. coruscus.     

Three species of Mytilus and their hybrids identified in a Scottish Loch: natives, relicts and invaders?

Three species of the mussel, Mytilus, occur in the North Atlantic region, M. edulis, M. galloprovincialis and M. trossulus, and hybrid zones are present where their distributions overlap. M. edulis is a native species in the UK. M. galloprovincialis originated in the Mediterranean and its distribution extends northwards along the Atlantic seaboard to Scotland. Baltic Sea mussels have a M. trossulus ancestry but are highly introgressed by M. edulis. In recent decades, farming of mussels on long-line rope culture systems has been introduced into Scotland. On farms in Loch Etive, a form of mussel with a fragile shell and a different shape to either M. edulis or M. galloprovincialis has been increasing in frequency over recent years. Samples of fragile shelled, normal strong shelled and intermediate mussel types were sampled from two farms in 2006 and compared with samples of M. edulis, M. galloprovincialis and M. trossulus from other sources where their species identity is well established. Abundance relative to depth, shell strength, condition index and shell morphology were analysed together with 5 allozyme loci and one nuclear DNA genetic marker (Me 15/16). The fragile shelled mussels, and many of those classed as intermediate, were identified as a mixture of M. trossulus and M. trossulus x M. edulis hybrids. This identification was strongly supported by both morphological and genetic data and is the first record of the presence of M. trossulus in UK waters. M. trossulus in Loch Etive are most likely to be a post-glacial relict population restricted to the low salinity area of the Loch that has recently increased in abundance due to commercial mussel growing activity. In addition, individual mussels of all three species and their hybrids were detected amongst Loch Etive mussels. This is the first genetic demonstration of all three species and their hybrids occurring together in one location in the Atlantic region and provides a unique opportunity to study the processes of speciation, divergence, and introgression in the genus Mytilus.     

The Substantial First Impact of Bottom Fishing on Rare Biodiversity Hotspots: A Dilemma for Evidence-Based Conservation

This study describes the impact of the first passage of two types of bottom-towed fishing gear on rare protected shellfish-reefs formed by the horse mussel Modiolus modiolus (L.). One of the study sites was trawled and the other was scallop-dredged. Divers collected HD video imagery of epifauna from quadrats at the two study sites and directed infaunal samples from one site.The total number of epifaunal organisms was significantly reduced following a single pass of a trawl (90%) or scallop dredge (59%), as was the diversity of the associated community and the total number of M. modiolus at the trawled site. At both sites declines in anthozoans, hydrozoans, bivalves, echinoderms and ascidians accounted for most of the change. A year later, no recovery was evident at the trawled site and significantly fewer infaunal taxa (polychaetes, malacostracans, bivalves and ophuroids) were recorded in the trawl track.The severity of the two types of impact reflected the undisturbed status of the habitats compared to previous studies. As a ‘priority habitat’ the nature of the impacts described on M. modiolus communities are important to the development of conservation management policy and indicators of condition in Marine Protected Areas (EU Habitats Directive) as well as indicators of ‘Good Environmental Status’ under the European Union Marine Strategy Framework Directive.Conservation managers are under pressure to support decisions with good quality evidence. Elsewhere, indirect studies have shown declines of M. modiolus biogenic communities in fishing grounds. However, given the protected status of the rare habitat, premeditated demonstration of direct impact is unethical or illegal in Marine Protected Areas. This study therefore provides a unique opportunity to investigate the impact from fishing gear whilst at the same time reflecting on the dilemma of evidence-based conservation management.     

Molecular and morphological evidence of hybridization between native Ruditapes philippinarum and the introduced Ruditapes form in Japan

Marine aquaculture and stock enhancement are major causes of the introduction of alien species. A good example of such an introduction is the Japanese shortneck clam Ruditapes philippinarum, one of the most important fishery resources in the world. To meet the domestic shortage of R. philippinarum caused by depleted catches, clams were imported to Japan from China and the Korean peninsula. The imported clam is an alien species that has a very similar morphology, and was misidentified as R. philippinarum (hereafter, Ruditapes form). We genotyped 1,186 clams of R. philippinarum and R. form at four microsatellite loci, sequenced mitochondrial DNA (COI gene fragment) of 485 clams, 34 of which were R. variegatus, and measured morphometric and meristic characters of 754 clams from 12 populations in Japan and China, including the Ariake Sea and Tokyo Bay, where large numbers of R. form were released. Our analyses confirmed that R. form was from the genus Ruditapes, and the genetic differentiation between R. philippinarum and R. form was distinct, but small, compared with five bivalve outgroups. However, R. form had distinct shell morphology, especially larger numbers of radial ribs on the shell surface, suggesting that R. form might be a new Ruditapes species or a variation of R. philippinarum that originated from southern China. A genetic affinity of the sample from the Ariake Sea to R. form was found with the intermediate shell morphology and number of radial ribs, and the hybrid proportion was estimated at 51.3 ± 4.6 % in the Ariake Sea.     

Studies on the prolonged storage of Metarhizium anisopliae conidia: effect of temperature and relative humidity on conidial viability and virulence against mosquitoes

The shell lengths, dried shell weights, soft tissue wet weights, and soft tissue dry weights were ascertained for noninfected Ilyanassa obsoleta and for the same snail species naturally infected with the following digeneans: Himasthla quissetensis, Zoogonus lasius, Cercaria dipterocerca, Lepocreadium setiferoides, Microphalloides nassicola, Stephanostomum tenue, and Microbilharzia variglandis. Analyses of the data obtained indicate that infection with all of the trematodes listed above causes neither enhanced growth of soft tissues nor accelerated lengthening of the shell. However, snails infected with sporocysts of Z. lasius have significantly heavier shells than do noninfected snails. These data suggest that infection with Z. lasius may have caused enhanced growth in the form of increased calcium deposition in the shell of I. obsoleta, possibly as a result of parasitic castration. In addition, the mean dry weight of the soft tissues of snails infected with M. variglandis, when normalized for shell length, is significantly lower than that of noninfected snails, possibly as a result of parasite-induced pathology. Finally, comparisons among infected snails indicate a trend toward increased soft tissue dry weight in snails infected with L. setiferoides, although the mean dry weight of these snails does not differ significantly from the mean dry weight of noninfected snails.     

Ontogeny and evolution within the Myophorellidae (Bivalvia): Paedomorphic trends

The role of heterochronic phenomena in molluscan evolution is insufficiently understood but potentially significant. The aim of this paper is to explore some paedomorphic trends in the evolution of the Myophorellidae (Bivalvia: Trigoniida). Early ontogeny of general shell shape and ornamentation of one species of Steinmanella was analyzed and compared to data obtained for three species of Myophorella: two belonging to the subgenus M. (Promyophorella) (one from the Jurassic and one from the Cretaceous) and one belonging to the Jurassic M. (Myophorella). For general shell shape, a geometric morphometric analysis was performed on lateral views of the shells. Regarding ornamentation, flank costal disposition on the marginal carina, tubercle separation and relative development of the sub-commarginal subset of flank costae were quantified. A qualitative analysis was also performed. A two-trend shell shape development is considered as primitive. The first trend is marked by a relative reduction of the posterior margin together with a relative elongation of the shell. A tangential opisthogyrate growth component characterizes the second trend. There is a transitional stage where both trends interact. Early flank ornamentation is characterized by two or three sub-commarginal costae, continuous through the area, after which oblique costae with fine tubercles start to form. The subgenus M. (Myophorella) evolved by paedomorphic retention of juvenile shell shape and ornamentation, resulting in a large shell with coarse tubercles. Shell morphology in Steinmanella evolved by paedomorphic suppression of the primitive second trend in the development of the shell, resulting in an orthogyrate shell shape, and the retention of juvenile ornamentation (coarse tubercles, more sub-commarginal costae, juvenile rates of costal disposition). The paedomorphic (most likely by deceleration) retention of juvenile shell morphology within the Myophorellidae seems to have been recurrent within the group, resulting in many cases of convergence, and obscuring the phylogenetic relationships among its species.     

Characterization of a novel shell matrix protein with vWA domain from Mytilus coruscus

ABSTRACT

Mollusk shell is a product of biomineralization with excellent mechanical properties, and the shell matrix proteins (SMPs) have important functions in shell formation. A vWA domain-containing protein (VDCP) was identified from the shell of Mytilus coruscus as a novel shell matrix protein. The VDCP gene is expressed at a high level in specific locations in the mantle and adductor muscle. Recombinant VDCP (rVDCP) showed abilities to alter the morphology of both calcite and aragonite, induce the polymorph change of calcite, bind calcite, and decrease the crystallization rate of calcite. In addition, immunohistochemistry analyses revealed the specific location of VDCP in the mantle, the adductor muscle, and the myostracum layer of the shell. Furthermore, a pull-down analysis revealed eight protein interaction partners of VDCP in shell matrices and provided a possible protein–protein interaction network of VDCP in the shell.     

The effects of sediment type on growth rate and shell allometry in the soft shelled clam Mya arenaria L

Hatchery-reared juvenile Mya arenaria L. were grown for 11 wk in replicated gravel, sand, mud, and pearl net treatments under flow-through sea-water conditions in Maine. Analyses of variance showed significant differences between sediment treatments for final shell length, dry meat weight, chondrophore growth increment, and percent shell weight. Growth of juvenile M. arenaria was more rapid in fine sediments than in coarse sediments or nets.Regression slopes of shell length-shell height and shell length-shell depth varied significantly between sediment treatments. Slower-growing clams from nets and gravel were more globose than clams from sand or mud treatments. Clams grown in sand were longer and narrower than those from mud. Differences in growth rates and shell form were attributed primarily to the physical properties of the substrata, and their effects on the scope for growth of M. arenaria.     

Assessment of the adaptation capabilities of the bivalves Modiolus modiolus (Linnaeus, 1758) and Crenomytilus grayanus (Dunker, 1853) under increased levels of heavy metals in the environment

The active biomonitoring method was used to examine the changes in heavy-metal (Fe, Zn, Cu, Cd, Mn, Pb, and Ni) contents in the organs (muscle, gonads, mantle, gills, digestive gland, and kidney) of the mussels Crenomytilus grayanus and Modiolus modiolus. The dynamics of trace element concentrations in mussel organs during the experiment were compared with their subcellular distribution. The defense strategy of M. modiolus consisted of the threshold accumulation of toxic metals in all organs followed by their excretion, whereas the strategy of C. grayanus involved short-term isolation from adverse environmental influence. Under chronic pollution, in C. grayanus the main loads occurred in the digestive gland and kidney. Under acute changes in environmental conditions, the processes of regulation (detoxification/excretion) of Fe, Mn, and Pb in this species were impaired substantially.     

Identification of Meloidogyne Species on the Basis of Head Shape and,Stylet Morphology of the Male

Head shape and stylet morphology of males of 90 populations of M. arenaria, M. hapla, M. incognita, and M. javanica from geographic regions of the world were compared by light microscopy (LM). In addition, stylets of one population each of M. arenaria, M. incognita, and M. javanica and three different chromosomal forms of M. hapla race A and two of race B were excised and examined with a scanning electron microscope (SEM). Differences among species occurred in both head and stylet morphology. Head morphology differed in size and shape of the head cap, annulation of the head region, and width of the head region relative to the first body annule. Differences in stylets occurred in size and shape of the cone, shaft, and knobs. All populations of M. hapla, except one, had similar head morphology, but stylet morphology was different between cytological races A and B. Populations of M. javanica varied with respect to the presence of head annulations. Head shape and stylet morphology of males are recommended as additional characters useful in the identification of root-knot nematodes.     

Evidence for extreme sequence divergence between the male‐ and female‐transmitted mitochondrial genomes in the bivalve mollusc,Modiolus modiolus (Mytilidae)

Marine mussels of the family Mytilidae, as well as a number of other bivalves, have a unique system of mitochondrial DNA inheritance called doubly uniparental inheritance (DUI). DUI is characterized by the presence of an ‘F’ mitochondrial genome that is transmitted through mothers to daughters and sons, and an ‘M’ mitochondrial genome that is transmitted only from fathers to sons. In this paper, we demonstrate that DUI exists in the horse mussel, Modiolus modiolus (Linnaeus, 1758) and compare the pattern of molecular evolution of the M and F types in this species. Total DNA was isolated from M. modiolus male and female gonad tissues, as well as from spawned sperm cells. From these DNA samples, partial mitochondrial DNA fragments were amplified from both cytochrome c oxidase subunit I (cox1), and 16S ribosomal RNA (rrnL) genes. Based on cox1 and rrnL sequences, heteroplasmy was observed in M. modiolus and characterized by the resolution of two mitotypes: an F mitotype present in tissues of both males and females, and an M mitotype present in spawned sperm. Using standardized p‐distance and Tamura‐Nei values, M. modiolus is found to display the highest M/F conspecific sequence divergence for any member of the family Mytilidae (i.e. 38% M/F sequence divergence, which is 9% higher than any other intraspecific M/F comparison for the family Mytilidae when standardized using p‐distances across all taxa observed). Sequence analysis also indicated that the M. modiolus M mitotype evolves significantly faster than its conspecific F type. The findings discussed herein broaden the range of mytilid species known to exhibit DUI and they also establish a new threshold for the genetic divergence of male mytilid mitochondrial genomes.     

Morphological Comparison of Head Shape and Stylet Morphology of Second-stage Juveniles of Meloidogyne Species

Head shape and stylet morphology of second-stage juveniles of one population each of M. incognita, M. javanica, M. arenaria, and M. hapla were compared by light microscopy. Excised stylets of each species were also compared by scanning electron microscopy (SEM). Differences in head morphology were observed only between M. hapla and the other three species. In SEM, differences in stylet size, shape, and relative distance of the dorsal esophageal gland orifice to the base of the stylet were evident. Differences in stylet morphology between M. incognita and M. javanica could not he detected by light microscopy, but M. arenaria and M. hapla could be distinguished from each other and from the other two species. Head shape and styler morphology of second-stage juveniles are considered useful taxonomic characters.     

Features of the shell morphology of Mytilus trossulus (Bivalvia: Mytilidae) in the fouling of the alga Sargassum pallidum (Phaeophyceae: Sargassaceae)

The features of ontogenetic variation in the shell shape of the bivalve Mytilus trossulus were studied based on material that was collected from different biotopes in the Vostok Bay of the Sea of Japan in 2011. It was revealed that the mollusks had different shell shapes in rock populations and in foulings of artificial substrates but all the developmental changes fall within formerly recorded peculiarities. It is shown that significant deviations from the typical form of the shell are characteristic to mollusks from the fouling of thalli of the brown algae Sargassum pallidum that inhabit shallow water at surf-exposed rocky headlands. The mollusks from this biotope were characterized by numerous traces of deformations of the shell, an atypically skewed growth of the rear edge, and a significant excess (20–25%) of the width over the shell height. It was revealed that the recorded features of shell morphology are apparently associated with features of mussel habitation in an environment with active hydrodynamics.     

Filamentous Growth of Mucor rouxii Under Nitrogen

The form of growth of Mucor rouxii (National Regional Research Laboratory 1894) under nitrogen is dependent on inoculum size. With a large inoculum (10⁶ spores inoculated per ml), the morphology consists mainly of swollen spores with some filaments and yeastlike cells. At lower inoculum levels growth is filamentous. The morphology of this strain on incubation under nitrogen and the dependence of the form of growth on inoculum size are similar to those found previously for other strains of M. rouxii.     

Genetics and taxonomy of Chilean smooth-shelled mussels, Mytilus spp. (Bivalvia: Mytilidae)

It has been previously established that native smooth-shelled mussels in southern South America possess close evolutionary affinities with Northern-Hemisphere Mytilus edulis L. 1758 (McDonald et al. (1991) [5]). This result has since been challenged by authors claiming that Chilean mussels should be considered a local subspecies of M. galloprovincialis Lmk. 1819. Moreover, morphological, physiological, ecotoxicological and molecular genetic studies on Chilean smooth-shelled mussels still frequently refer to ‘M. chilensis’ Hupé 1854, even though the previous discovery of alien M. galloprovincialis and considerable heterogeneity in shell morphology among samples collected along the Chilean shores raise concerns that different Mytilus spp. species might have been included under ‘M. chilensis’. Here we reviewed the molecular and morphological data available on smooth-shelled mussels from Chile in an attempt to clarify both their genetic composition and their taxonomic status. Using multivariate analysis on sample × allozyme-frequency matrices, we confirmed the widespread occurrence of the Southern-Hemisphere form of M. edulis along the shores from the North Patagonia region of Chile to the southern tip of the South American continent. The populations sampled in southern central Chile showed some evidence of slight introgression from Southern-Hemisphere M. galloprovincialis. Morphological characterization of a sample from Dichato in southern central Chile was consistent with its previous genetic identification as Mediterranean M. galloprovincialis. The occurrence of Southern-Hemisphere M. galloprovincialis in Punta Arenas at the southern tip of the South American continent was also reported. Southern-Hemisphere M. edulis, including native Chilean smooth-shelled Mytilus, should be assigned subspecific rank and named M. edulis platensis d’Orbigny 1846.     

Comparative Analysis of Subcellular Distribution of Heavy Metals in Organs of the Bivalve Mollusks <Emphasis Type="Italic">Crenomytilus grayanus</Emphasis> and <Emphasis Type="Italic">Modiolus modiolus</Emphasis> in a Continuously Polluted Environment

The distribution of Zn, Fe, Ni, Cu, Mn, Cd, and Pb in subcellular fractions, and of Cd, Zn, and Cu in cytoplasm proteins of the kidney and digestive gland of the mussels Crenomytilus grayanus and Modiolus modiolus, sampled from contaminated and conditionally clean areas, was studied. It was found that, in a contaminated environment, the organs of mussels were more highly enriched with metals. It was shown that essential trace elements were accumulated mostly in the cytosol of organs of both molluscan species from contaminated areas, whereas in the background areas the trace elements were associated mostly with membrane structures in Gray's mussel, C. grayanus, and with the cytosol in M. modiolus, the northern horse mussel. The lead was bound mostly to membrane structures in organs of both mussel species at all stations. The method of gel chromatography enabled us to isolate metallothionein-like proteins from the kidney of the northern horse mussel sampled in contaminated areas, whereas their concentration in the kidney of Gray's mussels was lower than the limiting error of the method. It is supposed that in the kidney of Gray's mussel the synthesis of metallothionein-like proteins was quenched by the integrated effect of the accumulated metals.     

Parataxonomic review of the Upper Cretaceous dinosaur eggshells belonging to the oofamily Megaloolithidae from India and Argentina

The eggshell oospecies from India and Argentina are compared and reviewed in detail. These eggshells resemble each other in having a nodular outer surface ornamentation and clearly arched growth lines of the shell units. Microstructurally, the eggshell oospecies belonging to the oofamily Megaloolithidae shows fan-like shell units, which are sharply separated from each other throughout the thickness of the eggshell and can be traced up to the surface of the eggshell. Comparisons between four oospecies from India and Argentina reveal three groupings, which show similarities between megaloolithids of both countries: (1) Megaloolithus jabalpurensis, M. matleyi and M. patagonicus; (2) M. cylindricus, M. rahioliensis and Tipo 1d; and (3) M.megadermus and Tipo 1e. The other two types of eggshell oospecies from India and Argentina show partially fused external nodes and shell units. As a result, growth lines enter into the adjacent shell units with a marked concavity. A new oogenus Fusioolithus have been erected due to fusion between shell units and tubospherulitic morphotype, which include two new oospecies F. baghensis and F. berthei. Till date, morphostructurally, a total of 15 eggshell oospecies belonging to different oofamilies have been recorded from India and seven oospecies from Argentina.