Gastropoda: A class in the phylum MOLLUSCA comprised of SNAILS and slugs. The former have coiled external shells and the latter usually lack shells.Snails: Marine, freshwater, or terrestrial mollusks of the class Gastropoda. Most have an enclosing spiral shell, and several genera harbor parasites pathogenic to man.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.Biomphalaria: A genus of planorbid freshwater snails, species of which are intermediate hosts of Schistosoma mansoni.Lymnaea: A genus of dextrally coiled freshwater snails that includes some species of importance as intermediate hosts of parasitic flukes.Nematocyst: A double-walled capsule found in jellyfish and other CNIDARIA whose functions include prey capture, defense, locomotion, and attachment. Nematocysts contain toxic CNIDARIAN VENOMS which are injected into the victim via a barbed tubule.Fasciola: A genus of trematode liver flukes of the family Fasciolidae. Two species of this genus are F. hepatica and F. gigantica. The parasites are found in the liver and gallbladder and associated ducts in mammals and occasionally man. F. gigantica occurs rarely in man.RNA, Ribosomal, 18S: Constituent of the 40S subunit of eukaryotic ribosomes. 18S rRNA is involved in the initiation of polypeptide synthesis in eukaryotes.Disease Vectors: Invertebrates or non-human vertebrates which transmit infective organisms from one host to another.Phylogeny: The relationships of groups of organisms as reflected by their genetic makeup.Population Density: Number of individuals in a population relative to space.BrazilEcosystem: A functional system which includes the organisms of a natural community together with their environment. (McGraw Hill Dictionary of Scientific and Technical Terms, 4th ed)Seasons: Divisions of the year according to some regularly recurrent phenomena usually astronomical or climatic. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)DNA, Ribosomal: DNA sequences encoding RIBOSOMAL RNA and the segments of DNA separating the individual ribosomal RNA genes, referred to as RIBOSOMAL SPACER DNA.Reproduction: The total process by which organisms produce offspring. (Stedman, 25th ed)Sequence Analysis, DNA: A multistage process that includes cloning, physical mapping, subcloning, determination of the DNA SEQUENCE, and information analysis.MuseumsZoology: The study of animals - their morphology, growth, distribution, classification, and behavior.Classification: The systematic arrangement of entities in any field into categories classes based on common characteristics such as properties, morphology, subject matter, etc.Checklist: Aid for consistent recording of data such as tasks completed and observations noted.Deoxyribonucleases, Type II Site-Specific: Enzyme systems containing a single subunit and requiring only magnesium for endonucleolytic activity. The corresponding modification methylases are separate enzymes. The systems recognize specific short DNA sequences and cleave either within, or at a short specific distance from, the recognition sequence to give specific double-stranded fragments with terminal 5'-phosphates. Enzymes from different microorganisms with the same specificity are called isoschizomers. EC 3.1.21.4.Helix (Snails): A genus of chiefly Eurasian and African land snails including the principal edible snails as well as several pests of cultivated plants.France: A country in western Europe bordered by the Atlantic Ocean, the English Channel, the Mediterranean Sea, and the countries of Belgium, Germany, Italy, Spain, Switzerland, the principalities of Andorra and Monaco, and by the duchy of Luxembourg. Its capital is Paris.Roman World: A historical and cultural entity dispersed across a wide geographical area under the political domination and influence of ancient Rome, bringing to the conquered people the Roman civilization and culture from 753 B.C. to the beginning of the imperial rule under Augustus in 27 B.C. The early city built on seven hills grew to conquer Sicily, Sardinia, Carthage, Gaul, Spain, Britain, Greece, Asia Minor, etc., and extended ultimately from Mesopotamia to the Atlantic. Roman medicine was almost entirely in Greek hands, but Rome, with its superior water system, remains a model of sanitation and hygiene. (From A. Castiglioni, A History of Medicine, 2d ed pp196-99; from F. H. Garrison, An Introduction to the History of Medicine, 4th ed, pp107-120)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.Biology: One of the BIOLOGICAL SCIENCE DISCIPLINES concerned with the origin, structure, development, growth, function, genetics, and reproduction of animals, plants, and microorganisms.Neurophysiology: The scientific discipline concerned with the physiology of the nervous system.Memory, Long-Term: Remembrance of information from 3 or more years previously.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.Mytilus: A genus of marine mussels in the family MYTILIDAE, class BIVALVIA. The species MYTILUS EDULIS is the highly edible common mussel.Estivation: In certain living species, a period of dormancy during the summer months marked by decreased metabolism.Electronic Mail: Messages between computer users via COMPUTER COMMUNICATION NETWORKS. This feature duplicates most of the features of paper mail, such as forwarding, multiple copies, and attachments of images and other file types, but with a speed advantage. The term also refers to an individual message sent in this way.Animal Shells: The hard rigid covering of animals including MOLLUSCS; TURTLES; INSECTS; and crustaceans.Cercaria: The free-swimming larval forms of parasites found in an intermediate host.Diatoms: The common name for the phylum of microscopic unicellular STRAMENOPILES. Most are aquatic, being found in fresh, brackish, and salt water. Diatoms are noted for the symmetry and sculpturing of their siliceous cell walls. They account for 40% of PHYTOPLANKTON, but not all diatoms are planktonic.Ponds: Inland bodies of standing FRESHWATER usually smaller than LAKES. They can be man-made or natural but there is no universal agreement as to their exact size. Some consider a pond to be a small body of water that is shallow enough for sunlight to reach the bottom.Lichen Nitidus: A chronic inflammatory disease characterized by shiny, flat-topped, usually flesh-colored micropapules no larger than the head of a pin. Lesions are localized in the early stages, found chiefly on the lower abdomen, penis, and inner surface of the thighs. Distribution may become generalized as the disease progresses.Facial DermatosesNorth AmericaSelf-Fertilization: The fusion of a male gamete with a female gamete from the same individual animal or plant.Peroxisomes: Microbodies which occur in animal and plant cells and in certain fungi and protozoa. They contain peroxidase, catalase, and allied enzymes. (From Singleton and Sainsbury, Dictionary of Microbiology and Molecular Biology, 2nd ed)Digestive System: A group of organs stretching from the MOUTH to the ANUS, serving to breakdown foods, assimilate nutrients, and eliminate waste. In humans, the digestive system includes the GASTROINTESTINAL TRACT and the accessory glands (LIVER; BILIARY TRACT; PANCREAS).Pleurobranchaea: A genus of side-gilled sea slugs in the family Pleurobranchidae, superorder GASTROPODA. They are opportunistic voracious feeders but prefer the sea anemone.Minor Planets: Small solar system planetary bodies including asteroids. Most asteroids are found within the gap lying between the orbits of Mars and Jupiter.Turnera: A plant genus of the family Turneraceae, order Violales, subclass Dilleniidae, class Magnoliopsida.Calcium Carbonate: Carbonic acid calcium salt (CaCO3). An odorless, tasteless powder or crystal that occurs in nature. It is used therapeutically as a phosphate buffer in hemodialysis patients and as a calcium supplement.SwedenMagnesium Oxide: Magnesium oxide (MgO). An inorganic compound that occurs in nature as the mineral periclase. In aqueous media combines quickly with water to form magnesium hydroxide. It is used as an antacid and mild laxative and has many nonmedicinal uses.Electron Transport Complex IV: A multisubunit enzyme complex containing CYTOCHROME A GROUP; CYTOCHROME A3; two copper atoms; and 13 different protein subunits. It is the terminal oxidase complex of the RESPIRATORY CHAIN and collects electrons that are transferred from the reduced CYTOCHROME C GROUP and donates them to molecular OXYGEN, which is then reduced to water. The redox reaction is simultaneously coupled to the transport of PROTONS across the inner mitochondrial membrane.PubMed: A bibliographic database that includes MEDLINE as its primary subset. It is produced by the National Center for Biotechnology Information (NCBI), part of the NATIONAL LIBRARY OF MEDICINE. PubMed, which is searchable through NLM's Web site, also includes access to additional citations to selected life sciences journals not in MEDLINE, and links to other resources such as the full-text of articles at participating publishers' Web sites, NCBI's molecular biology databases, and PubMed Central.