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PubMed2006

Larval development of Brachidontes solisianus (Bivalvia, Mytilidae), with notes on differences between its hinge system and that of the mollusk Perna perna.

This work, which is part of a study program on meroplankton larvae, aims to gain more in-depth knowledge about planktonic larvae. This study began with the mollusk Brachidontes solisianus (Bivalvia-Mytilidae), which is abundant on the rocky shores of the Cabo Frio region (state of Rio de Janeiro, Brazil). Brachidontes solisianus larvae were grown under controlled conditions for a period of 26 days and were fed with Isochrysis galbana and Tetraselmis chui. The temperature was kept at 26 degrees C and the saltiness at 28. Images of the larvae were taken daily with a light camera and measured with a micrometric lens until settlement occurred. The average size of the first D-shaped veliger stage was 90 microm in length and 70 microm in height, while the size in the last stage before settlement (pediveliger) was 273 microm in length and 257 microm in height. The comparative study of the hinge system involved the most abundant intertidal species of the study area: Brachidontes solisianus and Perna perna. The B. solisianus species were found to have more visible denticles at the extremities of the provinculum, whereas the denticles of the P. perna species occur along the entire provinculum.

Animals↗
PubMed2000

[Genetic connections between some species of Mytilidae (Mollusca: Bivalvia) from the northern part of the Pacific Ocean].

In 1978 and 1999, seven and eight species of Mytilidae (Mollusca: Bivalvia) were analyzed using gel electrophoresis. Mean heterozygosity per individual (Hobs and Hexp) and genetic distances (Rogers' DR, Nei's DN, and others) were estimated for 21 and 24 allozyme loci. Mytilus modiolus had the highest variation among the species examined. Genetic distances were lowest for the M. trossulus-M. galloprovincialis species pair: DR = 0.147, DN = 0.078. Overall, five species of the genera Mytilus and Crenomytilus were genetically closer to each other (DR = 0.147, DN = 0.078) than to the remaining three species of this group (DR = 0.807, DN = 2.243). The relationships among the species were examined using cluster analysis and parsimony methods. The densest clusters in the dendrograms consisted of (1) M. trossulus and M. galloprovincialis and (2) M. coruscus, M. californianus, and M. grayanus. These two clusters form a larger cluster (3), which comprises all representatives of the nominal genus Mutilus and C. grayanus. The Mytilus-Crenomytilus cluster is consecutively joined by Adula falcatoides, Mytilus modiolus, and Septifer keenae. According to Nei's genetic distances DN, the time of divergence between M. trossulus and M. galloprovincialis is 0.8-1.6 Myr; between M. californianus and C. grayanus, it is approximately 9 Myr; and between M. coruscus and the latter pair, it is 13 Myr before present. Two representatives of the Mytilus ex gr. edulis complex diverged from the Mytilus-Crenomytilus group of large-size Pacific species about 20 Myr ago. These results are in good agreement with paleontological data and indicate a relatively recent origin of the Mytilus ex gr. edulis complex. The results obtained can be used in systematics and phylogeny of modern Mytilidae.

Animals↗
PubMed1990

Differentiation of the vitelline coat and the polarized site of sperm entrance in the egg of Unio elongatulus (Mollusca, Bivalvia).

We studied the differentiation of the polarized site of sperm entrance in the egg of a freshwater bivalve, Unio elongatulus. As previously shown, in this egg model the property of sperm recognition and binding is restricted to a region characterized by a wrinkled surface which surrounds a truncated cone or crater region, at the vegetal pole of the egg. The crater is formed during oogenesis at a site opposite the oocyte attachment to the ovarian wall. It first appears as a small bleb, and later detaches, leaving in the oocyte an open narrow process filled with an orderly array of microtubules. Here the vitelline coat differentiates from the rest of the oocyte. The role of the microtubules in the formation of the region and the differential distribution of the vitelline coat components is discussed. The synthesis during development of fucosyl containing glycoproteins and their presence in an electrophoretic pattern of isolated vitelline coats were also studied using Lotus tetragonolobus (LTA) conjugated with fluorescein and peroxidase.

Animals↗
PubMed2004

Mitochondrial DNA polymorphisms and sperm motility in Mytilus edulis (Bivalvia: Mytilidae).

The system of mitochondrial DNA (mtDNA) inheritance in Mytilus and other bivalves, termed doubly uniparental inheritance (DUI), is novel among animals. Males pass on their male transmitted (M-type) mtDNA from fathers to their sons whereas females pass on their female transmitted (F-type) mtDNA from mothers to both sons and daughters. Thus, Mytilus males contain two distinct types of mtDNA. Interestingly, sperm contains only the paternal mtDNA. Phylogenetic analysis has shown that some female types have been able to switch their route of inheritance. These "recently masculinized" mitochondrial genomes behave as a typical M-type in that they are transmitted from generation to generation through sperm. Because the "recently masculinized" and "standard" male mitotypes in M. edulis exhibit approximately 8.7% amino acid sequence divergence, we hypothesized that these differences could affect mitochondrial, and hence sperm, functions. Furthermore, since recently masculinized mitotypes have been shown to replace standard male types periodically over evolutionary timescales, we tested the hypothesis that sperm swimming speeds would be greater for males with recently masculinized M-type genomes. Sperm activity was videotaped, digitized and tracked. A linear mixed effects model found no significant difference in linear velocities or curvilinear speeds between the mitotypes suggesting that swimming speeds are similar for both in the period shortly after spawning.

Animals↗
PubMed1997

Morphological characterization of the hemocytes of the clam, Ruditapes decussatus (Mollusca: Bivalvia).

Hemocytes play an important role in internal defence in molluscs. The morphology of hemolymph cells was studied for the first time in Ruditapes decussatus. Two main types of hemocytes (hyalinocytes and granulocytes) exist in R. decussatus. Three types of granulocytes were identified by light microscopy, in accordance with the presence of basophilic or acidophilic granules or a mixture of both in the cytoplasm. The existence of hyalinocytes and granulocytes was confirmed by electron microscopy. Some monoclonal antibodies (MABs) raised against hemocytes of Crassostrea gigas showed cross-reactivity with the total population of hemocytes of R. decussatus; however, none of the MABs raised against hemocytes of Mytilus edulis showed cross-reactivity. The MABs assayed did not allow us to distinguish hemocyte subpopulations.

Animals↗
PubMed1997

Experimental field studies with Mya arenaria (Bivalvia) on the induction and effect of hematopoietic neoplasia.

A field experiment was conducted from 1991 to 1992 to examine induction and impact of hematopoietic neoplasia on the marine bivalve Mya arenaria in southeastern Massachusetts. Clams were collected from Little Buttermilk Bay and separated into three size classes (20-29, 30-39, and 40-49 mm shell length) in the laboratory. These sizes span the range of adults found in the population. A random subsample of these clams was taken to estimate disease prevalence at the start of the experiment, and this was found to be </=10% in all size classes. Remaining clams were assigned randomly to two groups: Control and Treated. "Controls" were injected with filtered seawater, while "Treated" clams were injected with hemocytes extracted from diseased individuals. Injection of diseased hemocytes was performed to increase disease prevalence in the Treated group. Clams were returned to New Bedford Harbor, a more contaminated field location, where hematopoietic neoplasia is more prevalent, in January 1991, and characteristics of both groups were monitored for 555 days. Among Controls, probability of survival was size-dependent, with higher survival rates in larger clams. Treated clams had a lower probability of survival than Controls, and the magnitude of treatment effect increased with size class. The impact on survival was evident after 89 days, but it was first shown to be statistically significant after 189 days. Among Controls, probability of disease was strongly season-dependent, increasing in the large size class from 0.19 in spring to 0.50 in summer. During summer, Treated clams had a higher probability of being diseased than Controls. Among survivors, no significant sublethal effects due to treatment were detected in the field experiment. Experimental manipulation of disease prevalence may be a useful tool in future studies. In addition to results pertaining to disease, this study obtained long-term growth information, by size class, on somatic and reproductive tissue and shell size.

Analysis of Variance↗
PubMed2000

Phylogenetic relationships among mytilidae (Bivalvia): 18S rRNA data suggest convergence in mytilid body plans.

Nearly complete sequences were determined for small-subunit (18S) rRNA genes from seven species representative of four subfamilies of Mytilidae: Modiolus modiolus and M. auriculatus (Modiolinae); Lithophaga lithophaga and L. nigra (Lithophaginae); Musculus senhousie and M. discors (Crenellinae); and Hormomya domingensis (Mytilinae). Small-subunit rRNA gene sequences were also determined for Solemya reidi (Subclass Protobranchia), Mya arenaria (Subclass Heterodonta), and Elliptio complanata (Subclass Paleoheterodonta) as outgroup taxa. Phylogenetic analyses including these and other nearly complete bivalve small-subunit rRNA sequences demonstrate support for the monophyly of the family Mytilidae and the subfamilies Crenellinae and Lithophaginae. However, the subfamilies Mytilinae and Modiolinae appear polyphyletic. Likelihood, parsimony, and distance analyses support the placement of H. domingensis (Mytilinae) in a clade with G. demissa (Modiolinae). This clade is distinct from those containing other species traditionally assigned to these two subfamilies. Kishino-Hasegawa tests support these nontraditional relationships, suggesting that the mytiliform and/or modioliform body plans have evolved independently in at least two mytilid lineages.

Animals↗
PubMed1981

Monoamine precursor uptake in ganglia of a mollusc Anodonta cygnea L. (Bivalvia) An autoradiographic and ultrastructural study.

In vitro-uptake and localization of 3H-5 hydroxytryptophan and 3H-dihydroxyphenylalanine have been investigated by means of light microscopic autoradiography in the central nervous system of the freshwater mussel, Anodonta cygnea L. Accumulation of the labelled monoamine precursors could be observed both over neuronal perikarya and neuropil in the ganglia. 3H-5-hydroxytryptophan and 3H-dihydroxyphenylalanine were taken up by neurons characterized by a small size (10-20 micrometer), a polygonal form and an intense staining with toluidine blue. Labelled axon branches situated either in the neuropil or between nerve cells in the cortex exhibited only a moderate activity, frequently of a diffuse character. After pretreatment fro 24 h with colchicine, silver grains were also seen over a neuronal perikarya and some axon profiles. This shows that local uptake of the monoamine precursors and, presumably, the synthesis of the monoamines takes place both at perikaryal and axonal/terminal level. The nerve cells accumulating the monoamine precursors contain a nucleus with rich chromatin content and a deeply invaginate nuclear envelope. Further ultrastructural characteristics of these neurons are their well-developed rough endoplasmic reticulum system, a great number of mitochondria and glycogen granules, and the presence of dense-cored vesicles of different types. All those features are responsible for the electron-dense appearance of the cytoplasm.

5-Hydroxytryptophan↗
PubMed1983

Enkephalin-like immunoreactivity in the pedal ganglion of Mytilus edulis (Bivalvia) and its proximity to dopamine-containing structures.

The presence of enkephalin-like immunoreactivity in the pedal ganglion of the bivalve mollusc Mytilus edulis has been demonstrated. Enkephalin-like immunoreactivity is highly localized in those intraganglionic regions rich in dopamine-containing structures. In addition, FMRF-NH2-like (Phe-Met-Arg-Phe-HN2) immunoreactivity was found to occur in intraganglionic regions that are devoid of enkephalin-like immunoreactivity. The differential topographic distribution of these peptidergic immunoreactivities suggests involvement in separate functions. By contrast, the closeness of enkephalin-like immunoreactivity to dopamine histofluorescence supports previous data demonstrating biochemical and physiological links between these two systems.

Animals↗
PubMed1976

Cytochemical and immunofluorescence investigations of insulin-like producing cells in the intestine of Mytilus edulis L. (Bivalvia).

Insulin-like immunoreactivity can be localized to cells of the intestine in the area of the hepatopancreas of Mytilus edulis L. No cross-reactivity can be obtained with anti-glucagon, anti-gastrin, anti-pentagastrin or anti-caerulin. The cells containing the substance immunoreactive to mammalian anti-insulin, can be restrained with paraldehyde-fuchsin.

Animals↗
PubMed1977

The nacreous layer in Mytilus, Nucula, and Unio (Bivalvia). Crystalline composition and nucleation of nacreous tablets.

Etching with the glutaraldehyde-acetic acid solution reveals that the nacreous tablets in Mytilus, Nucula, and Unio are composed of four crystal individuals which occur in two structurally different pairs and which are probably cyclically twinned. In Mytilus, one pair consists of horizontal lamellae, whereas the other pair lacks the lamellae. The lamellar pair of crystals is considerably less soluble in the etching solution than the non-lamellar pair. In the less-soluble crystal pair of Nucula and Unio, the lamellar structure is absent. In all three genera, the nucleation of new nacreous tablets invariably takes place on the top surface of the less-soluble crystal individuals. The stack-like growth of the nacreous tablets in the marginal region of the shell in Nucula is probably related to the exceptionally large-sized, less-soluble crystal individuals in the nacreous tablets of this region.

Acetates↗
PubMed1996

Phylogenetic analysis of Veneridae (Bivalvia): comparison of molecular and palaeontological data.

An approximately 400-bp-long portion of the 16s rRNA gene sequence has been determined for the venerid clams Chamelea gallina (Chioninae), Dosinia lupinus (Dosiniinae), Pitar rudis, Callista chione (Pitarinae), Tapes decussatus, T. philippinarum, Venerupis (= Paphia) aurea (Tapetinae), and Venus verrucosa (Venerinae). Neighbor-joining and maximum parsimony trees support the results of traditional classification methods at the subfamily level but do not support the concept of a genus Tapes. The transversion divergence rate estimated on the basis of the palaeontological record for the C. gallina/V. verrucosa separation and for the Pitarinae is very close (0.14-0.16% per Myr, respectively) to that of ungulates and cetaceans, while the Tapetinae exhibit a much higher (0.36% per Myr) rate.

Animals↗
PubMed1999

The small-subunit rRNA gene sequences of venerids and the phylogeny of bivalvia.

The complete nucleotide sequence of the 18S subunit of ribosomal DNA (rDNA) was determined for the venerid clams Callista chione (Pitarinae) and Venus verrucosa (Venerinae). Comparison of the new sequences with the published sequences of 1 annelid, 2 gastropods, 2 polyplacophorans, and 19 bivalves showed that when the annelids are used as outgroup the gastropods diverge from the bivalves, which form a cluster including the polyplacophorans. When the gastropods alone were compared with the bivalves, the latter split in two groups corresponding to the two subclasses of Heterodonta and Pteriomorpha. The former include two taxa that diverged early, Galeomma and Tridacna, while the Veneridae and Mactridae form two sister groups. In contrast to previous reports and in line with morphological data, the Ostreidae are included in the Pteriomorphia and form a monophyletic group.

Animals↗
PubMed2004

Unique evolution of Bivalvia arginine kinases.

The clams Pseudocardium, Solen, Corbicula and Ensis possess a unique form of arginine kinase (AK) with a molecular mass of 80 kDa and an unusual two-domain structure, a result of gene duplication and subsequent fusion. These AKs also lack two functionally important amino acid residues, Asp(62) and Arg(193), which are strictly conserved in other 40-kDa AKs and are assumed to be key residues for stabilizing the substrate-bound structure. However, these AKs show higher enzyme activity. The cDNA-derived amino acid sequences of 40-kDa AKs from the blood clam Scapharca broughtonii and the oyster Crassostrea gigas were determined. While Asp(62) and Arg(193) are conserved in Scapharca AK, these two key residues are replaced by Asn and Lys, respectively, in Crassostrea AK. The native enzyme from Crassostrea and both of the recombinant enzymes show an enzyme activity similar to that of two-domain clam AKs and at least twofold higher than that of other molluskan AKs. Although the replacement of Asp(62) or Arg(193) by Gly in normal AK causes a considerable decrease in V(max) (6-15% of wild-type enzyme) and a two- to threefold increase in K(m) for arginine, the same replacement in Scapharca AK had no pronounced effect on enzyme activity. Together with the observation that bivalve AKs are phylogenetically distinct from other molluskan AKs, these results suggest that bivalve AKs have undergone a unique molecular evolution; the characteristic stabilizing function of residues 62 and 193 has been lost and, consequently, the enzyme shows higher activity than normal.

Amino Acid Sequence↗