Bivalvia: A class in the phylum MOLLUSCA comprised of mussels; clams; OYSTERS; COCKLES; and SCALLOPS. They are characterized by a bilaterally symmetrical hinged shell and a muscular foot used for burrowing and anchoring.Mytilidae: A family of marine MUSSELS in the class BIVALVIA.Mollusca: A phylum of the kingdom Metazoa. Mollusca have soft, unsegmented bodies with an anterior head, a dorsal visceral mass, and a ventral foot. Most are encased in a protective calcareous shell. It includes the classes GASTROPODA; BIVALVIA; CEPHALOPODA; Aplacophora; Scaphopoda; Polyplacophora; and Monoplacophora.Pectinidae: A large family of mollusks in the class BIVALVIA, known commonly as scallops. They possess flat, almost circular shells and are found in all seas from shallow water to great depths.Unionidae: A family of freshwater mussels in the class BIVALVIA. They differ from ZEBRA MUSSELS in that they are larger and posses a larval stage called glochidia, which requires attachment to the GILLS or fins of particular species of FISHES.Gills: Paired respiratory organs of fishes and some amphibians that are analogous to lungs. They are richly supplied with blood vessels by which oxygen and carbon dioxide are exchanged directly with the environment.Perna: A genus of freshwater mussel in the family MYTILIDAE, class BIVALVIA. It is found in tropical and warm temperate coastal waters. Most species have green in their shells.Symbiosis: The relationship between two different species of organisms that are interdependent; each gains benefits from the other or a relationship between different species where both of the organisms in question benefit from the presence of the other.Rivers: Large natural streams of FRESH WATER formed by converging tributaries and which empty into a body of water (lake or ocean).Atlantic OceanDNA, Mitochondrial: Double-stranded DNA of MITOCHONDRIA. In eukaryotes, the mitochondrial GENOME is circular and codes for ribosomal RNAs, transfer RNAs, and about 10 proteins.Phylogeny: The relationships of groups of organisms as reflected by their genetic makeup.Sequence Analysis, DNA: A multistage process that includes cloning, physical mapping, subcloning, determination of the DNA SEQUENCE, and information analysis.RNA, Ribosomal, 16S: Constituent of 30S subunit prokaryotic ribosomes containing 1600 nucleotides and 21 proteins. 16S rRNA is involved in initiation of polypeptide synthesis.Molecular Sequence Data: Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.DNA, Ribosomal: DNA sequences encoding RIBOSOMAL RNA and the segments of DNA separating the individual ribosomal RNA genes, referred to as RIBOSOMAL SPACER DNA.Bacteria: One of the three domains of life (the others being Eukarya and ARCHAEA), also called Eubacteria. They are unicellular prokaryotic microorganisms which generally possess rigid cell walls, multiply by cell division, and exhibit three principal forms: round or coccal, rodlike or bacillary, and spiral or spirochetal. Bacteria can be classified by their response to OXYGEN: aerobic, anaerobic, or facultatively anaerobic; by the mode by which they obtain their energy: chemotrophy (via chemical reaction) or PHOTOTROPHY (via light reaction); for chemotrophs by their source of chemical energy: CHEMOLITHOTROPHY (from inorganic compounds) or chemoorganotrophy (from organic compounds); and by their source for CARBON; NITROGEN; etc.; HETEROTROPHY (from organic sources) or AUTOTROPHY (from CARBON DIOXIDE). They can also be classified by whether or not they stain (based on the structure of their CELL WALLS) with CRYSTAL VIOLET dye: gram-negative or gram-positive.Evolution, Molecular: The process of cumulative change at the level of DNA; RNA; and PROTEINS, over successive generations.Fresh Water: Water containing no significant amounts of salts, such as water from RIVERS and LAKES.Acari: A large, subclass of arachnids comprising the MITES and TICKS, including parasites of plants, animals, and humans, as well as several important disease vectors.Corbicula: A genus of freshwater clams, in the family Corbiculidae, class BIVALVIA. It originated in Asia but was introduced in North America and is now found throughout the United States.Spisula: A genus of surf clams in the family Mactridae, class BIVALVIA. They are often used in EMBRYOLOGY research.Echinostomatidae: A family of flukes (TREMATODA) characterized by a collar of spines at their anterior end. The body is elongated and is covered with spines, and the two suckers are usually close together. (Noble et al., Parasitology: the Biology of Animal Parasites, 6th ed, p183)Karyotyping: Mapping of the KARYOTYPE of a cell.In Situ Hybridization, Fluorescence: A type of IN SITU HYBRIDIZATION in which target sequences are stained with fluorescent dye so their location and size can be determined using fluorescence microscopy. This staining is sufficiently distinct that the hybridization signal can be seen both in metaphase spreads and in interphase nuclei.Heterochromatin: The portion of chromosome material that remains condensed and is transcriptionally inactive during INTERPHASE.Spermatozoa: Mature male germ cells derived from SPERMATIDS. As spermatids move toward the lumen of the SEMINIFEROUS TUBULES, they undergo extensive structural changes including the loss of cytoplasm, condensation of CHROMATIN into the SPERM HEAD, formation of the ACROSOME cap, the SPERM MIDPIECE and the SPERM TAIL that provides motility.Axoneme: A bundle of MICROTUBULES and MICROTUBULE-ASSOCIATED PROTEINS forming the core of each CILIUM or FLAGELLUM. In most eukaryotic cilia or flagella, an axoneme shaft has 20 microtubules arranged in nine doublets and two singlets.Sperm Tail: The posterior filiform portion of the spermatozoon (SPERMATOZOA) that provides sperm motility.Sperm Motility: Movement characteristics of SPERMATOZOA in a fresh specimen. It is measured as the percentage of sperms that are moving, and as the percentage of sperms with productive flagellar motion such as rapid, linear, and forward progression.Mytilus: A genus of marine mussels in the family MYTILIDAE, class BIVALVIA. The species MYTILUS EDULIS is the highly edible common mussel.Mytilus edulis: A species of mussel in the genus MYTILUS, family MYTILIDAE, class BIVALVIA, known as the common mussel. It has a bluish-black shell and is highly edible.Marine Biology: The study of the origin, structure, development, growth, function, genetics, and reproduction of organisms which inhabit the OCEANS AND SEAS.Muscle Proteins: The protein constituents of muscle, the major ones being ACTINS and MYOSINS. More than a dozen accessory proteins exist including TROPONIN; TROPOMYOSIN; and DYSTROPHIN.Genome, Mitochondrial: The genetic complement of MITOCHONDRIA as represented in their DNA.Materia Medica: Materials or substances used in the composition of traditional medical remedies. The use of this term in MeSH was formerly restricted to historical articles or those concerned with traditional medicine, but it can also refer to homeopathic remedies. Nosodes are specific types of homeopathic remedies prepared from causal agents or disease products.Paleontology: The study of early forms of life through fossil remains.North AmericaBiological Evolution: The process of cumulative change over successive generations through which organisms acquire their distinguishing morphological and physiological characteristics.Journal Impact Factor: A quantitative measure of the frequency on average with which articles in a journal have been cited in a given period of time.BooksMicrobiology: The study of microorganisms such as fungi, bacteria, algae, archaea, and viruses.Internet: A loose confederation of computer communication networks around the world. The networks that make up the Internet are connected through several backbone networks. The Internet grew out of the US Government ARPAnet project and was designed to facilitate information exchange.Students: Individuals enrolled in a school or formal educational program.Computer-Assisted Instruction: A self-learning technique, usually online, involving interaction of the student with programmed instructional materials.Cardiidae: A family of bivalve MOLLUSKS with heart-shaped shells, commonly known as cockles. Unlike most BIVALVES, cockles are hermaphroditic.Ostreidae: A family of marine mollusks in the class BIVALVIA, commonly known as oysters. They have a rough irregular shell closed by a single adductor muscle.Shellfish: Aquatic invertebrates belonging to the phylum MOLLUSCA or the subphylum CRUSTACEA, and used as food.South Australia: A state in south central Australia. Its capital is Adelaide. It was probably first visited by F. Thyssen in 1627. Later discoveries in 1802 and 1830 opened up the southern part. It became a British province in 1836 with this self-descriptive name and became a state in 1901. (From Webster's New Geographical Dictionary, 1988, p1135)Encyclopedias as Topic: Works containing information articles on subjects in every field of knowledge, usually arranged in alphabetical order, or a similar work limited to a special field or subject. (From The ALA Glossary of Library and Information Science, 1983)GreenlandMongolia: The country is bordered by RUSSIA on the north and CHINA on the west, south, and east. The capita is Ulaanbaatar.Tooth: One of a set of bone-like structures in the mouth used for biting and chewing.Fossils: Remains, impressions, or traces of animals or plants of past geological times which have been preserved in the earth's crust.Hydrology: Science dealing with the properties, distribution, and circulation of water on and below the earth's surface, and atmosphere.