C

C4 pathway Also called the Hatch-Slack pathway of photosynthesis; CO₂ is initially fixed in mesophyll cells into malate and aspartate.

cadre Sclerotized mouth lining of a pentastomid.

caecum Intestine; also see cecum.

calabar swelling Transient subcutaneous nodule, provoked by the filarial nematode Loa loa.

Calcaneus calc = heel bone.

Calcarea The class of sponges whose members are small and possess monaxon, triaxon, or tetraaxon calcium carbonate spicules.

calcareous Made of calcium carbonate.

calcareous ooze A type of biogenous sediment that is made of the calcium carbonate shells and skeletons of marine organisms.

calciferous glands Glands in an earthworm that secrete calcium ions into the gut.

calcitonin A thyroid hormone that lowers calcium and phosphate levels in the blood; also called thyrocalcitonin.

calcium carbonate (CaCO₃) A mineral that is the major component of the shell, skeleton, and other parts of many organisms.

callose A complex carbohydrate found in the sieve areas of sieve-tube elements; particularly abundant at the time of injury.

callus An undifferentiated group of cells formed as a response to wounding (as at the base of a stem) or in tissue culture.

calorie Unit of heat defined as the amount of heat required to heat 1 g of water from 14.5 to 15.5C; 1 cal = 4.184 joules in the International System of Units.

Calorie Amount of heat energy required to raise the temperature of 1,000 g of water 1C.

calotte "Head" end of a dicyemid mesozoan.

Calvin Cycle Biochemical pathway in photosynthesis in which carbon from atmospheric CO₂ is fixed and reduced into carbohydrate.

calypter Squama or lobe in the anal angle of a dipteran wing.

calyx 1. A boat-shaped or cuplike central body of an entoproct or crinoid. The body and tentacles of an entoproct. 2. A cuplike set of ossicles that support the crown of a sea lily or feather star (class Crinoidea, phylum Echinodermata).

CAM See Crassulacean acid metabolism.

Cambrian A geological period of the Paleozoic beginning about 590 million years ago and lasting about 85 million years, during which time many divisions of protists occurred in the oceans.

camerostome Ventral groove in the propodosoma of soft ticks wherein lies the capitulum.

campestral Characteristic of rural locations, especially open country and grasslands.

campodeiform Insect larva with well-defined head and thoracic appendages; typically predatory.

Canaliculus A small canal.

cancellous Having a spongy or porous structure.

cancer Invasive, out-of-control cell growth that results in malignant tumors.

canine canis = a dog. A tooth.

cannulation The introduction of a substance to a tissue (e.g., an area of the brain) via hollow electrode, fine tube (cannula), or needle.

canopy The upper portion of a population of plants; the term is usually associated with forests and agricultural crops.

capillary A small blood vessel that connects an arteriole and a venule; the functional unit of the circulatory system.

capillary pores Small spaces in the soil that become filled with a fluid (such as water) because of the adhesion of particles to the matrix (solid substrate) and the cohesion of the water molecules to themselves.

capitate caput = head; ate = like.

capitulum Anterior of two basic body regions of a mite or tick. Also called a gnathosoma.

capsid The protein coat of a virus.

capsule (1) A simple fruit that develops from a compound ovary with two or more carpels; capsules dehisce in many ways. example: cotton. (2) The sporangium of a bryophyte.

captacula Tentacles extending from head of scaphopod molluscs, used in feeding.

captive breeding Raising plants or animals in zoos or other controlled conditions to produce stock for subsequent release into the wild.

carageenan A polysaccharide extracted from red algae and used for many industrial products.

carapace Structure formed by posterior and lateral extension of dorsal sclerites of the head in many Crustacea, usually covering and/or fusing with one or more thoracic somites; considered as arising from a fold of head exoskeleton. Also a dorsal sclerotized plate often covering the idiosoma of acarines. The dorsal portion of the shell of a turtle. Formed from a fusion of vertebrae, ribs, and dermal bone.

carbaminohemoglobin Compound formed by the union of carbon dioxide and hemoglobin.

carbohydrate Compounds of carbon, hydrogen, and oxygen having the generalized formula (CH₂O)n; aldehyde or ketone derivatives of polyhydric alcohols, with hydrogen and oxygen atoms attached in a 2:1 ratio.

carbon (C ) An element that is an essential constituent of all organic compounds.

carbon cycle The circulation and reutilization of carbon atoms, especially via the processes of photosynthesis and respiration.

carbon dating A procedure used to determine the age of fossils.

carbon dioxide (CO₂) A colorless gas that is required in the process of photosynthesis.

carbon fixation The conversion of inorganic carbon into energy-rich organic carbon, usually by photosynthesis.

carbon monoxide (CO ) Colorless, odorless, nonirritating but highly toxic gas produced by incomplete combustion of fuel, incineration of biomass or solid waste, or partially anaerobic decomposition of organic material.

carbon sink Places of carbon accumulation, such as in large forests (organic compounds) or ocean sediments (calcium carbonate); carbon is thus removed from the carbon cycle for moderately long to very long periods of time.

carbon skeleton The central portion of any organic molecule consisting only of the carbon molecule.

carbon source Originating point of carbon that reenters the carbon cycle; cellular respiration and combustion.

carbonic acid Atmospheric CO₂ dissolved in water to yield H₂CO₃, a weak acid.

Carboniferous A geological period of the Paleozoic beginning approximately 360 million years ago and lasting about 85 million years. During this time forests appeared and became dominant, composed of arborescent club mosses, horsetails, and ferns. Their extinction resulted in the formation of coal deposits.

carboxyl The acid group of organic molecules _COOH.

carboxyl group An acid group attached to a molecule; _COOH.

carcinogens Substances that cause cancer.

cardiac Belonging or relating to the heart.

cardiac muscle Specialized type of muscle tissue found only in the heart.

cardioactive glycoside Sugar-containing molecules with an active compound that affects the heartbeat.

cardiovascular system See circulatory system.

carinate Having a keel, in particular the flying birds with a keeled sternum for the insertion of flight muscles.

carnauba wax A high quality, hard industrial wax extracted from the carnauba palm tree.

carnivore One of the flesh-eating mammals of the order Carnivora. Also, any organism that eats animals. Adj., carnivorous.

carotene A red, orange, or yellow pigment belonging to the group of carotenoids; precursor of vitamin A.

carotenoids Class of plant pigments that includes carotenes and xanthophylls; most are yellow, orange, or red.

Carotid karos = stupor; L. carot = a carrot.

Carpal karpos = wrist.

carpel The reproductive unit of angiosperms composed of a placental surface and ovules. A component of the gynoecium.

carpellate A unisexual flower having carpels but no stamens.

carpospore spores produced by the carposporophyte form of red algae

carposporophyte A diploid generation found in the red algae. It produces non-motile carpospores.

carrageenan Gelatinous material extracted from the walls of some red algae and used in a variety of commercial and industrial products.

Carrion's disease Bacterial disease transmitted by sand flies. See also Oroya fever and verruga peruana.

carrying capacity Maximum number of a population that can be supported by the environment over a given period of time.

cartilage Type of connective tissue in which cells are located within lacunae and are separated by a semisolid matrix. Provides a site for muscle attachment, aids in movement of joints, and provides support.

cartilaginous fishes Fishes with a skeleton made of cartilage: sharks, rays, skates, and ratfishes (or chimaeras).

caryopsis Simple, dry, indehiscent fruit with a single seed that is fused to the ovary wall. Also called a grain. Example: wheat.

cash crops Crops that are sold rather than consumed or bartered.

Casparian strip Water-impermeable strip of suberin found in the transverse and radial walls of endodermal cells.

caste One of the polymorphic forms within an insect society, each caste having its specific duties, as queen, worker, soldier, and so on.

catabolic Chemical reactions that release energy by degrading complex compounds into simpler ones.

catabolism Destructive metabolism; process in which complex molecules are reduced to simpler ones.

catadromous Refers to fishes that migrate from fresh water to the ocean to spawn.Compare anadromous.

catalysis An increase in the velocity of a chemical reaction or process produced by the presence of a substance that is not consumed in the net chemical reaction or process.

catalyst A substance that accelerates a chemical reaction but does not become a part of the end product.

catastrophic systems Dynamic systems that jump abruptly from one seemingly steady state to another without any intermediate stages.

catkin Inflorescence of unisexual flowers.

Cauda Tail.

caudal Having to do with, or toward, the tail of an animal.

caudal fin The posterior, or tail, fin of fishes.

caudal peduncle The area where the caudal fin joins the rest of a fish's body.

caudal Constituting, belonging to, or relating to a tail.

Caudofoveata The class of molluscs characterized by a wormlike shell-less body and scalelike calcareous spicules; lack eyes, tentacles, statocysts, crystalline style, foot, and nephridia. Deep-water marine burrowers. Chaetoderma.

caveolae The invaginated vesicles and pits in potocytosis.

Cavum cavus = hollow. Cavity.

cDNA See complementary DNA.

cecum 1. Each arm of the blind-ending Y-shaped digestive tract of trematodes (phylum Platyhelminthes). 2. A region of the vertebrate digestive tract where fermentation can occur. It is located at the proximal end of the large intestine.

cecum, caecum A blind pouch at the beginning of the large intestine; any similar pouch.

celiac koilia = belly.

cell Minute biological compartments within which the processes of life are carried out.

cell body Portion of a nerve cell that includes a cytoplasmic mass and a nucleolus, and from which the nerve fibers extend.

cell culture (tissue culture)The culture of single cells or tissues to form callus and then to develop whole plants asexually.

cell cycle The regular sequence of events during which a cell grows, prepares for division, duplicates its contents, and divides to form two daughter cells.

cell enlargement The expansion in volume of a cell typically as a result of increasing turgor pressure.

cell plate Double membrane across the equator of a dividing cell that develops from the phragmoplast; it marks where the new cell walls will form.

cell wall The rigid outermost layer of the cells found in plants, some protists, and most bacteria. Found in plants composed principally of cellulose.

cell-mediated immune response Immune response involving cell surfaces only, not antibody production, specifically the TH1 arm of the immune response. Contrast humoral immune response.

cell-mediated immunity (CMI) Immunity in which antigen is bound to receptor sites on the surface of sensitized T lymphocytes that have been produced in response to prior immunizing experience with that antigen and in which manifestation is through macrophage response with no intervention of antibody.

cellular immune response Binding of antigen with receptor sites on sensitized T lymphocytes to cause release of lymphokines that affect macrophages, a direct response with no intervention of antibody. Also, the entire process by which the body responds to an antigen, resulting in a condition of cell-mediated immunity.

cellular respiration The process in which a cell breaks down sugar or other organic compounds to release energy used for cellular work; may be anaerobic or aerobic, depending on the availability of oxygen.

cellulase An enzyme that breaks down cellulose.

cellulose Chief polysaccharide constituent of the cell wall of green plants and some fungi; an insoluble carbohydrate (C₆H₁₀O₅)n that is converted into glucose by hydrolysis.

cement glands Glands in a male acanthocephalan that produce secretions sealing the female reproductive tract after copulation.

cementation Compacting and natural "gluing together" of sedimentary deposits to form sedimentary rocks.

Cenozoic A geological era beginning 65 million years ago and extending to the present, characterized by major adaptive radiation of specialized life forms and formation of biomes.

central bud The main bud in a cluster located at one position.

central cell Also known as the polar cell, this is the binucleated cell in the center of an embryo sac containing the two haploid polar nuclei.

central dogma The relationship among the steps from DNA to the production of a protein. The synthesis of messenger RNA from DNA, and the movement mRNA out of the nucleus (transcription). Carries the genetic code into the cytoplasm. Within the cytoplasm, ribosomes and transfer RNA convert this genetic code in messenger RNA into a protein (translation).

central nervous system (CNS) That part of the nervous system that is condensed and centrally located; for example, the brain and spinal cord of vertebrates and the brain and ganglia of insects.

central place foragers Animals that collect more than one food item at a time and bring the items to a central location for storage or feeding to offspring.

central rift valley A depression in the mid-ocean ridge .

central vacuole A membrane-enclosed sac that takes up most of the volume of a mature plant cell.

centrifugal force The force that tends to push a body away from the center of rotation.

centriole A minute cytoplasmic organelle usually found in the centrosome and considered to be the active division center of the animal cell; organizes spindle fibers during mitosis and meiosis. Same structure as basal body or kinetosome.

centrolecithal Pertaining to an insect egg with the yolk concentrated in the center.

centrolecithal egg Type of egg found in many arthropods, in which the nucleus is located centrally in a small amount of nonyolky cytoplasm, surrounded by a large mass of yolk. After fertilization and some nuclear divisions, the nuclei migrate to the periphery to proceed with superficial cleavage, the yolk remaining central.

centromere Constricted region of a mitotic chromosome that holds sister chromatids together; also the site on the DNA where the kinetochore forms and then captures microtubules from the mitotic spindle.

centrosome Minute body in cytoplasm of many plant and animal cells that contains one or two centrioles and is the center of dynamic activity in mitosis.

Centrum kentron = center.

Cephalaspidomorphi The class of vertebrates characterized by the absence of paired appendages and the presence of sucking mouthparts with teeth and a rasping tongue. Lampreys.

cephalic Having to do with, or toward, the head of an animal.

cephalization The development of a head with an accumulation of nervous tissue into a brain.

Cephalochordata The subphylum of chordates whose members possess a laterally compressed, transparent body. They are fishlike and possess all four chordate characteristics throughout life. Amphioxus.

cephalogaster Contractile organ in adult epicaridean isopods that functions in sucking blood and perhaps in respiration.

cephalopods Octopuses, squids, and other molluscs that possess a foot modified into arms that surround the head.

cephalothorax A body division found in many Arachnida and higher Crustacea, in which the head is fused with some or all of the thoracic segments.

cerata Fingerlike projections along the dorsal sides of some nudibranches.

cerato- keras = horn.

cercaria Juvenile digenetic trematode, produced by asexual reproduction within a sporocyst or redia. Cercaria are freeswimming and have a digestive tract, suckers, and a tail. They develop into a metacercaria.

cerci Appendages on the 11th abdominal somite of some insects; usually sensory.

cercomer Posterior, knoblike attachment on a procercoid or cysticercoid. It usually bears the hooks of the oncosphere.

cereals Members of the grass family that yield a large amount of grain rich in carbohydrates, fats, proteins, and vitamins.

cerebellum Portion of the brain that coordinates skeletal muscle movement. Part of the metencephalon, it consists of two hemispheres and a central vermis.

cerebrum The main portion of the brain, occupying the upper part of the cranial cavity; its two hemispheres are united by the corpus callosum; forms the largest part of the central nervous system in mammals.

cervical Relating to a neck.

cervicis cervix = neck; deer.

Cestoidea The class of platyhelminthes that has members that are all parasitic with no digestive tract; have great reproductive potentials. Tapeworms.

cetaceans (order Cetacea)Marine mammals with anterior flippers, no posterior limbs, and a dorsal fin: whales, dolphins, and porpoises.

chaetognaths See arrow worms.

chaetotaxy Taxonomic study of the location and arrangement of bristles on an insect. Especially important in the order Diptera.

chaff Bracts surrounding a cereal grain; removed during threshing.

Chagas' disease Disease of humans and other mammals caused by Trypanosoma cruzi.

chagoma Reddish nodule that forms at the site of entrance of Trypanosoma cruzi into the skin.

chain reaction A self-sustaining reaction in which the fission of nuclei produces subatomic particles that cause the fission of other nuclei.

chalazal Ovule end opposite the micropyle.

chalimus Specialized, parasitic copepodid, found in the copepod order Siphonostomatoida; attached to its host by an anterior "frontal filament" that is secreted by the frontal gland.

chaotic systems Systems that exhibit variability, which may not be necessarily random, yet whose complex patterns are not discernible over a normal human timescale.

chaparral A relatively dry biome that occurs in the southwestern United States. Plants are low and shrubby and have tough, waxy leaves. Animals include insects, rodents, rabbits, lizards, snakes, and mule deer.

character A component of phenotype (including specific molecular, morphological, behavioral or other features) used by systematists to diagnose species or higher taxa, or to evaluate phylogenetic relationships among different species or higher taxa, or relationships among populations within a species.

character displacement The process by which two closely related species interact so as to cause one or both of them to diverge evolutionarily in one or more traits.

charging. In protein synthesis, a reaction catalyzed by tRNA synthetase, in which an amino acid is attached to its particular tRNA molecule.

charophytes A group of green algae characterized by calcified filaments that have nodes and internodes.

chelate Condition of an arthropod appendage in which the subterminal podomere bears a distal process to form a pincer with the terminal podomere; sometimes (incorrectly) used to describe the subchelate condition.

chelicera One of a pair of the most anterior head appendages on the members of the subphylum Chelicerata, which include spiders, ticks, and mites; generally the most important feeding appendages in these groups.

Chelicerata The subphylum of arthropods whose members have a body that is divided into prosoma and opisthoma. The first pair of appendages are feeding appendages called chelicerae. Spiders, scorpions, mites, and ticks.

chelipeds Pincerlike first pair of legs in most decapod crustaceans; specialized for seizing and crushing.

chemical bond The force that holds molecules together.

chemical element A substance that cannot be separated into different substances by ordinary chemical methods; see element.

chemical synapse A synapse at which neurotransmitters released by one neuron diffuse across an extracellular gap to influence a second neuron's activity.

chemiosmosis The process whereby a proton gradient and an electrochemical gradient are generated by electron transport and then used to drive ATP synthesis by oxidative phosphorylation.

chemistry The science dealing with the elements and atomic relations of matter, and various elemental compounds. The study of the properties of substances and how substances react with one another.

chemoautotroph An organism utilizing inorganic compounds as a source of energy.

chemolithoautotroph An organism that synthesizes organic matter by oxidizing inorganic compounds.

chemoreceptor A receptor that is stimulated by the presence of certain chemical substances.

chemosynthesis Autotrophic synthesis of organic compounds by certain bacteria; uses energy from inorganic compounds.

chemosynthetic (chemoautotrophic) bacteria Autotrophic bacteria (such as the sulfur bacteria) that use energy by releasing it from particular chemical compounds.

chemotaxis Orientation movement of cells or organisms in response to a chemical stimulus.

chemotaxonomy Using the identification of groups of chemical compounds as genetic indicators in the establishment of taxonomic relationships.

chemotroph An organism that derives nourishment from inorganic substances without using chlorophyll.

chiasma A decussation or X-shaped crossing; the places where pairs of homologous chromatids remain in contact during late prophase to anaphase of the first meiotic division. The chiasma indicates where an exchange of homologous segments has taken place between nonsister chromatids by crossing over.

chief cel l Cell of a gastric gland that secretes various digestive enzymes, including pepsinogen.

chigger Mite of the family Trombiculidae. Also, sometimes applied to Tunga penetrans, the chigoe flea.

Chilopoda The class of uniramous arthropods whose members have one pair of legs per segment and whose body is oval in cross section. Centipedes.

chinampas Long, narrow strips of land bordered on three sides by irrigation canals which can produce several crops per year.

chitin 1.The polysaccharide found in the exoskeleton of arthropods.2. High molecular weight polymer of N-acetyl glucosamine linked by 1,4-b-glycosidic bonds.

chitons (class Polyplacophora)Molluscs that have a shell divided into eight overlapping plates.

chlamydospore Thick-walled dormant spore in fungi.

chloragogen tissue Cells covering the dorsal blood vessel and digestive tract of annelids; function in glycogen and fat synthesis and urea formation.

chlorenchyma Parenchyma tissue containing chloroplasts as in the leaf mesophyll.

chloride cells Cells in the gills of fishes that are involved in the excretion of excess salts.

chlorinated hydrocarbons (or organochlorides)Nonbiodegradable and synthetic chemical pollutants used as pesticides.

chlorocruorin A greenish iron-containing respiratory pigment dissolved in the blood plasma of certain marine polychaetes.

chlorofluorocarbons (CFCs)Chemicals used in sprays and other products that affect the ozone layer.

chlorogogen cells Modified peritoneal cells, greenish or brownish, clustered around the digestive tract of certain annelids; apparently they aid in elimination of nitrogenous wastes and in food transport.

chlorophyll Green pigment found in plants and in some animals; necessary for photosynthesis.

Chlorophyta A division of protists commonly referred to as the green algae. May be unicellular, multicellular, or coenocytic.

chloroplast A plastid containing chlorophyll and usually other pigments, found in cytoplasm of plant cells.

Choana choane = funnel. Nasal passage.

choanocyte One of the flagellate collar cells that line cavities and canals of sponges.

choanomastigote Like a promastigote but with the flagellum emerging from a collarlike process, as in Crithidia spp.

cholesterol Steroid that is an integral part of cell membranes and a precursor to other steroidal compounds in animals.

cholinergic Type of nerve fiber that releases acetylcholine from axon terminal.

Chondrichthyes The class of vertebrates whose members are fishlike, possess paired appendages and a cartilaginous skeleton, and lack a swim bladder. Skates, rays, and sharks.

Chorda A cord or string.

chordamesoderm Tissue in the amphibian gastrula that forms between ectoderm and endoderm in the dorsal lip region of the blastopore; develops into the mesoderm and notochord.

Chordata A phylum of animals whose members are characterized by a notochord, pharyngeal gill slits, a dorsal tubular nerve cord, and a postanal tail.

chordates Animals that display a hollow dorsal nerve cord, gill slits, and a notochord. Includes the protochordates and the vertebrates.

chorion The outer of the double membrane that surrounds the embryo of reptiles, birds, and mammals; in mammals it contributes to the placenta.

chorioptic mange Disease caused by mites of the genus Chorioptes.

choroid Delicate, highly vascular membrane; in vertebrate eye; the layer between the retina and sclera.

chromaffin tissue Specialized endocrine cells located near the kidneys.

chromatid A replicated chromosome joined to its sister chromatid by the centromere; separates and becomes daughter chromosome at anaphase of mitosis or anaphase of the second meiotic division.

chromatin Nuclear material that gives rise to chromosomes during mitosis; complex of DNA, histones, and nonhistone proteins.

chromatoid bar Masses of RNA, visible with light microscopy, in young cysts of Entamoeba spp.

chromatophore Pigment cell, usually in the dermis, in which usually the pigment can be dispersed or concentrated.

chromomere One of the chromatin granules of characteristic size on the chromosome; may be identical with a gene or a cluster of genes.

chromonema A convoluted thread in prophase of mitosis or the central thread in a chromosome.

chromoplast Membrane-bound organelle containing pigments other than chlorophyll; the pigments may be yellow, orange, or red.

chromosome Rodlike structure that appears in the nucleus of a cell during mitosis; contains the genes responsible for heredity. Structure composed of a very long DNA molecule and associated proteins that carries part (or all) of the hereditary information of an organism.

chronic effects Long-lasting results of exposure to a toxin; can be a permanent change caused by a single, acute exposure or a continuous, low-level exposure.

chronic food shortages Long- term undernutrition and malnutrition; usually caused by people's lack of money to buy food or lack of opportunity to grow it themselves.

chrysalis The pupal case of a butterfly that forms from the exoskeleton of the last larval instar.

Chrysophyta A division of protists consisting of golden-brown and yellow-green algae as well as the diatoms.

chylomicron A particle of the class of lipoproteins responsible for the transport of cholesterol and triglycerides from the small intestine to tissues after meals.

chyluria Lymph in the urine, characterized by a milky color.

chyme Semifluid mass of food materials that pass from the stomach to the small intestine.

ciguatera A type of poisoning found in tropical fishes. It may result from a toxin produced by a dinoflagellate.

cilia Microscopic, hairlike processes on the exposed surfaces of certain eukaryotic cells. Cilia contain a core bundle of microtubules and are capable of performing repeated beating movements. They are also responsible for the swimming of many single-celled organisms.

ciliary comb One of eight bands of cilia fused at the base that is found in comb jellies.

ciliary creeping The principal means of nemertine locomotion.

ciliary organelles Organelles of specialized function formed by the fusion of cilia.

ciliates A group of protozoans that have cilia.

Ciliophora The protozoan phylum characterized by members with simple or compound cilia at some stage in their life history; heterotrophs with a well-developed cytostome and feeding organelles; at least one macronucleus and micronucleus present. Examples: Paramecium, Stentor, Vorticella, Balantidium.

cilium A short, hair-like flagellum that is found in large numbers and used in movement, for pushing food particles, and in other functions.

in moving particles along the cell surface or, in ciliate protozoans, for locomotion.

cinclides Small pores in the external body wall of sea anemones for extrusion of acontia.

circadian Occurring at a period of approximately 24 hours.

circadian rhythms Daily cycles of activity. Circadian rhythms are usually based upon photoperiods.

circalunadian rhythm A cycle of repeating activity each lunar day, or 24.8 hours.

circannual rhythm A biological rhythm of about a year in length or period.

circle of poisons Importation of food contaminated with pesticides banned for use in this country but made here and sold abroad.

circulation cells Air movement in a circular pattern from the earth's surface up into the outer atmosphere and then back down again; produce high and low pressure systems and dictate precipitation patterns at different latitudes.

circulatory system Pertaining to the circulation. Also cardiovascular system.

circumcision The removal of all or part of the prepuce or foreskin.

cirri Any of various slender or filamentous, usually flexible appendages, such as one of the compound organelles composed of groups of fused cilia seen in certain peritrichious ciliate protozoa that are used for locomotion; an eversible penis in flatworms; a fingerlike projection of a polychete parapodium.

Cirripedia The class of crustaceans whose members are sessile and highly modified as adults. Enclosed by calcium carbonate valves. Barnacles.

cirrus A hairlike tuft on an insect appendage; locomotor organelle of fused cilia; male copulatory organ of some invertebrates.

cisternae Space between membranes of the endoplasmic reticulum within cells.

cistron A series of codons in DNA that code for an entire polypeptide chain.

citric acid cycle A series of chemical reactions in the mitochondrion by which various molecules are oxidized and energy is released from them; Krebs cycle, TCA or tricarboxylic acid cycle.

Citric Acid Cycle Another name for Krebs Cycle.

city A differentiated community with a sufficient population and resource base to allow residents to specialize in arts, crafts, services, and professional occupations.

clade A taxon or other group consisting of an ancestral species and all of its descendants, forming a distinct branch on a phylogenetic tree.

cladistics A system of arranging taxa by analysis of evolutionarily derived characteristics so that the arrangement will reflect phylogenetic relationships.

cladogram A branching diagram showing the pattern of sharing of evolutionarily derived characters among species or higher taxa.

cladophyll A stem or branch that resembles a leaf.

clamp Complex set of sclerotized bars, forming a "pinching" organ on the opisthaptor of a monogenetic trematode.

clasper A copulatory organ along the inner edge of each pelvic fin in male sharks and other cartilaginous fishes.

class Taxonomic rank consisting of related orders.

classical (Pavlovian) conditioning A type of learning whereby an unconditioned stimulus (US) that elicits a specific response (unconditioned response [UCR]) is paired with a neutral stimulus (becomes the conditioned stimulus [CS]) so that the response becomes conditioned (CR).

clathrin A protein forming a lattice structure lining the invaginated pits during receptor-mediated endocytosis.

clavicle Key, clavicle.

claw The sharp, usually curved, nail on the foot of an animal or insect. The pincerlike extremity of specific limbs of certain arthropods (e.g., lobster claws).

clay The smallest soil particle size at less than .002 mm

cleaning symbiosis The type of symbiosis in which the smaller partner regularly removes parasites from fishes.

clear-cut Cutting every tree in a given area, regardless of species or size; an appropriate harvest method for some species; can be destructive if not carefully controlled.

cleavage The early mitotic and cytoplasmic divisions of an embryo.

Cleido- Key, clavicle.

climacteric rise A point during the ripening process of certain fruit when the respiration rates rise to very high levels.

climate A description of the long-term pattern of weather in a particular area.

climatology The study of climates and the factors influencing them.

climax Stage of relative stability attained by a community of organisms, often the culminating development of a natural succession. Also, orgasm.

climax community A self-perpetuating, more-or-less stable community of organisms that continues as long as environmental conditions under which it developed prevail. The final stage in an ecological succession.

cline A pattern of directional, often gradual, change in phenotype or genotype of populations across a geographic transect.

clitellum The region of an annelid responsible for secreting mucus around two worms in copula and for secreting a cocoon to protect developmental stages.

cloaca Posterior chamber of digestive tract in many vertebrates, receiving feces and urogenital products. In certain invertebrates, a terminal portion of digestive tract that serves also as respiratory, excretory, or reproductive tract.

clone A series of identical cells or individuals that have developed from a single cell or individual.

closed canopy A forest where tree crowns spread over 20 percent of the ground; has the potential for commercial timber harvests.

closed circulatory system A circulatory system in an animal in which blood is confined to vessels throughout its circuit.

cloud forests High mountain forests where temperatures are uniformly cool and fog or mist keeps vegetation wet all the time.

clouds of electrons The distribution of electrons in space around the atomic nucleus.

Cnidaria The phylum of animals whose members are characterized by radial or biradial symmetry, diploblastic organization, a gastrovascular cavity, and nematocysts. Jellyfish, sea anemones, and their relatives.

cnidarians Invertebrates with nematocysts and radial symmetry.

cnidoblast See cnidocyte.

cnidocil Modified cilium on nematocyst-bearing cnidocytes in cnidarians; triggers nematocyst.

cnidocyte Modified interstitial cell that holds the nematocyst; during development of the nematocyst, the cnidocyte is a cnidoblast.

co-composting Microbial decomposition of organic materials in solid waste into useful soil additives and fertilizer; often, extra organic material in the form of sewer sludge, animal manure, leaves, and grass clippings are added to solid waste to speed the process and make the product more useful.

coacervate An aggregate of colloidal droplets held together by electrostatic forces.

coagulation Process in which a series of enzymes are activated, resulting in clotting of blood.

coal gasification The heating and partial combustion of coal to release volatile gases, such as methane and carbon monoxide; after pollutants are washed out, these gases become efficient, clean-burning fuel.

coal washing Coal technology that involves crushing coal and washing out soluble sulfur compounds with water or other solvents.

coarctate pupa Pupa in which the last larval cuticle is retained as a puparium.

coastal management The use of coastal resources with the intention of preserving them.

coastal plain estuary An estuary created by flooding a coastal river valley with seawater.

coastal shelf The shallow region of the ocean surrounding a large landmass.

coastal zone See neritic zone.

Coastal Zone Management Act Legislation of 1972 that gave federal money to thirty seacoast and Great Lakes states for development and restoration projects.

coat In reference to the eggshell of many cestodes, the portion contributed by the outer envelope, derived from embryonic blastomeres.

coccolith A small calcareous plate imbedded in the cell wall of coccolithophores, a type of phytoplankton.

coccolithophorids Unicellular, eukaryotic members of the phytoplankton that have calcareous, button-like structures, or coccoliths.

coccus Any of various spherical-shaped bacteria.

coccyx kokkyx = cuckoo. Anthropoid caudal vertebrae.

cochlea A tubular cavity of the inner ear containing the essential organs of hearing; occurs in crocodiles, birds, and mammals; spirally coiled in mammals.

cocoon Protective covering of a resting or developmental stage, sometimes used to refer to both the covering and its contents; for example, the cocoon of a moth or the protective covering for the developing embryos in some annelids.

codominance A condition in which both alleles of a heterozygous pair are expressed independently.

codon A sequence of three bases on messenger RNA that specifies the position of an amino acid in a protein.

coefficient of relationship The fraction of genes identical by common descent shared between two individuals.

coelacanths A group of lobed-fin fossil fishes. Latimeria was discovered alive in 1952.

coelenterates Cnidaria; a group of aquatic animals represented by hydras, sea anemones, jellyfish, and corals.

coelenteron Internal cavity of a cnidarian; gastrovascular cavity; archenteron.

coelom A fluid-filled body cavity, lined by mesodermlying between the gut and the outer body wall musculature that is lined with derivatives of the embryonic mesoderm.

coelomic fluid The fluid that fills the coelom of echinoderms and other invertebrates.

coelomocyte Another name for amebocyte; primitive or undifferentiated cell of the coelom and the water-vascular system.

coelomoduct A duct that carries gametes or excretory products (or both) from the coelom to the exterior.

coelozoic Living in the lumen of a hollow organ, such as the intestine.

coenecium, coenoecium The common secreted investment of an ectoproct colony; may be chitinous, gelatinous, or calcareous.

coenenchyme Extensive mesogleal tissue between the polyps of an alcyonarian (phylum Cnidaria) colony.

coenocyte Organisms possessing a large mass of cytoplasm with many nuclei.

coenocytic A tissue in which the nuclei are not separated by cell membranes; syncytial.

coenosarc The inner, living part of hydrocauli in hydroids.

coenurus Tapeworm metacestode in the family Taeniidae, in which several scolices bud from an internal germinative membrane; not enclosed in an internal secondary cyst.

coenzyme An organic nonprotein molecule, frequently a phosphorylated derivative of a water-soluble vitamin, that binds with the protein molecule (apoenzyme) to form the active enzyme (holoenzyme). Examples include biotin, NAD+, and coenzyme A.

coevolution The change in gene frequencies resulting from two species, acting as strong selective forces on one another.

cofactor A metal ion or inorganic ion with which an enzyme must unite in order to function.

cogeneration The simultaneous production of electricity and steam or hot water in the same plant.

cognition The processes in the minds of animals or their general mental functions, including perception, representation, and memory.

cohesion Tendency of like molecules to stick together, usually due to hydrogen bonds.

cold front A moving boundary of cooler air displacing warmer air.

coleoptile The meristematic growing tip of a grass.

coleorhiza Sheath surrounding the radicle (embryonic root) of monocotyledons.

coliform bacteria Bacteria that live in the intestines (including the colon) of humans and other animals; used as a measure of the presence of feces in water or soil.

collagen A tough, fibrous protein occurring in vertebrates as the chief constituent of collagenous connective tissue; also occurs in invertebrates, for example, the cuticle of nematodes.

collar cell (or choanocyte)A flagellated, food-trapping cell of sponges.

collenchyma Ground tissue in plants with unevenly thickened primary cell walls; functions in support.

collenchyme A gelatinous mesenchyme containing undifferentiated cells; found in cnidarians and ctenophores.

collencyte A type of cell in sponges that is star shaped and apparently contractile.

colleterial glands Female accessory glands in insects that produce a substance to cement eggs together or material for an ootheca.

Colliculus collis = hill; ulus = diminutive. Eye and ear reflex centers in the brain.

colloblast A glue-secreting cell on the tentacles of ctenophores.

colloid A two-phase system in which particles of one phase are suspended in the second phase.

colonial hypothesis A hypothesis formulated to explain the origin of multicellularity from protist ancestors; animals may have been derived when protists associated together and cells became specialized and interdependent.

colonial A multicellular organism that produces a colony of cells, usually referring to colonial algae.

colonization The pioneer establishment of vegetation on a previously unvegetated area.

colonizer An organism that initiates the biological "conquest" of soil or rock; see also pioneer organism.

colony A cluster of genetically identical individuals formed asexually from a single colonizing individual.

colostrum The first secretion of the mammary glands following the birth of an infant.

columella Central pillar in gastropod shells.

columnar In the form of a column.

comb jellies The invertebrates with a gelatinous body, radial symmetry, and eight rows of ciliary combs.

comb plate One of the plates of fused cilia that are arranged in rows for ctenophore locomotion.

comb rows Rows of cilia that serve as the locomotor organs of ctenophorans.

commensalism A relationship in which one individual lives close to or on another and benefits, and the host is unaffected; often symbiotic.

common name A regional name for well-known plants; in the language of the region, rather than in Latin, and not necessarily paralleling any scientific name.

commonality In learning, the inference of a phyletic, evolutionary relationship among the species exhibiting a particular type of learning.

communal nesting More than one female in a nest raising the young of more than one female.

communal resource management systems Resources managed by a community for long-term sustainability.

communication Act on the part of one organism (or cell) that alters the probability of patterns of behavior in another organism (or cell) in an adaptive fashion.

community diversity The number of different kinds of organisms living in an area.

community ecology The study of interactions of all populations living in the ecosystem of a given area.

community An assemblage of organisms that are associated in a common environment and interact with each other in a self-sustaining and self-regulating relation.

companion cell Phloem cell associated with a sieve tube member.

comparative anatomy The study of animal structure in an attempt to deduce evolutionary pathways in particular animal groups.

comparative embryology The study of animal development in an attempt to deduce evolutionary pathways in particular animal groups.

comparative method A comparison of the behavior of two or more species for the purpose of either elucidating some common aspects of the ecology and evolution of behavior or exploring the mechanisms underlying behavior.

comparative psychologist An ethologist who studies the genetic, neural, and hormonal bases of animal behavior.

comparative psychology A branch of psychology involving the study of animals. Some comparative psychologists are more concerned with learning, cognition, and intelligence in human and nonhuman animals, while others are indistinguishable from other animal behaviorists in that they explore the causation, development, evolution, and functional aspects of behavior in a broad range of species.

compartmentalization The division of labor in living cells such that enzymes related to a particular function are packaged and separated from the other cell contents, usually by a membrane.

compensation point The condition in a living system in which the uptake of CO₂ equals the release of CO₂; that is, photosynthesis equals respiration.

competition Some degree of overlap in ecological niches of two populations in the same community, such that both depend on the same food source, shelter, or other resources, and negatively affect each other's survival.

competitive exclusion principle The idea that two species with identical niches cannot coexist.

competitive exclusion A theory that no two populations of different species will occupy the same niche and compete for exactly the same resources in the same habitat for very long; disputed by some ecologists who see biological communities as highly individualistic and variable.

complement Collective name for a series of proteins that bind in a complex series of reactions to antibody (either IgM or IgG) when the antibody is itself bound to an antigen; produces lysis of cells if the antibody is bound to antigens on the cell surface.

complement fixation test Immunological method used to detect presence of antibodies that bind (or fix) complement; a standard diagnostic test for many infections.

complementary DNA (cDNA) DNA prepared by transcribing the base sequence from mRNA into DNA by reverse transcriptase; also called copy DNA.

complementary strand Two polynucleotide chains in which the pairing of adenine is always with thymine (in DNA) or uracil (in RNA), and guanine is always paired with cytosine.

complete flower A flower with all four floral whorls (sepals, petals, stamens, and carpels).

complete linkage Two genes positioned so close to one another on the same chromosome that recombination between them does not occur.

complete protein A protein that has all of the essential amino acids and in the correct proportions.

complex camera eye The type of image-forming eye found in squids and octopuses.

complexity (ecological)The number of species at each trophic level and the number of trophic levels in a community.

composite signal A signal formed by combining two or more simpler signals.

compost Partially decayed organic matter used in gardening and farming to enrich the soil and increase water holding capacity.

composting The biological degradation of organic material under aerobic (oxygen-rich) conditions to produce compost, a nutrient-rich soil amendment and conditioner.

compound A substance composed of atoms of two or more elements joined by chemical bonds and chemically united in fixed proportions.

compound eye An eye consisting of many individual lens systems (ommatidia). Present in many members of the phylum Arthropoda.

compound fruit A fruit consisting of several individual fruits held together (a multiple fruit) or in which separate carpels of a flower stay together (an aggregate fruit).

compound leaf A leaf composed of two or more completely independent blade units called leaflets.

compound pistil A pistil composed of more than one carpel.

compression A fossil formed when carbonized plant material is still present in the original shape but is greatly compressed and reduced in size by pressure.

compression wood The reaction wood produced along the lower side of leaning trees, straightening the trunk by expanding and pushing the tree upright.

concentration gradient The difference in concentration in two parts of a system.

concentricycloidea The class of echinoderms whose members are characterized by two concentric water-vascular rings encircling a disklike body; no digestive system; and internal brood pouches. Sea daisies.

conchae Thin bones in the nasal chamber.

concomitant immunity Premunition.

condensation The aggregation of water molecules from vapor to liquid or solid when the saturation concentration is exceeded.

condensation nuclei Tiny particles that float in the air and facilitate the condensation process.

condensation reaction A chemical reaction in which reactant molecules are combined by the removal of a water molecule (a hydrogen from one and a hydroxyl from the other reactant).

conditioned response (CR) The behavior pattern that becomes conditioned during classical conditioning.

conditioned stimulus (CS) The previously neutral stimulus that, through classical conditioning, now elicits the conditioned response.

conditioning A form of learning in which a behavior is associated with a reward such as food.

conduction The conveyance of energy, such as heat, sound, or electricity. The direct transfer of thermal motion (heat) between molecules of the environment and those on the body surface of an animal.

condyle A process on a bone used for articulation.

condyles Bearing surfaces between arthropod joints that provide the fulcra on which the joints move.

cone A vertebrate photoreceptor cell with a tapered outer segment; unlike rod cells, cone cells are usually sensitive

cone cell A color-sensitive photoreceptor cell concentrated in the retina.

confusion effect The reduced capture efficiency experienced by a predator caused by high densities or swarms of prey.

conidiophore Hyphae on which one or many conidia are produced.

conidiosporangium A structure that produces conidiospores.

conidiospore An asexual spore produced singly

conidium Asexual reproductive spores of some ascomycetes and imperfect fungi.

conifer Any of a group of plants that produce a strobilus or cone as a reproductive structure.

coniferous forest A community type dominated by cone-bearing gymnosperms mostly in the northern hemisphere.

conifers Needle-bearing trees that produce seeds in cones.

conjugation Temporary union of two ciliate protozoa while they are exchanging chromatin material and undergoing nuclear phenomena resulting in binary fission. Also, formation of cytoplasmic bridges between bacteria for transfer of plasmids.

connective tissue A basic type of tissue that includes bone, cartilage, and various fibrous tissues. Connective tissue serves to support and bind tissues together.

conoid Truncated cone of spiral fibrils located within the polar rings of the suborder Eimeriina.

conservation To protect, conserve the natural world and all its components.

conservation of matter In any chemical reaction, matter changes form; it is neither created nor destroyed.

Consolidated Metropolitan Statistical Area (CMSA) An area with more than one million people formed by the merger of two or more population centers meeting other specified requirements of the Census Bureau.

conspecific A member of the same species.

constant proportions, rule of A principle that states that the relative amounts of ions in seawater are always the same.

constraints In optimality models, the limits placed on an animal because of its inherent abilities.

consumer A heterotroph. A primary consumer feeds directly on a primary producer, whereas a secondary consumer feeds on a primary consumer.

consummatory behavior Actions of an animal completing a behavior sequence, as in consuming food, mating, etc.

consumption The fraction of withdrawn water that is lost in transmission or that is evaporated, absorbed, chemically transformed, or otherwise made unavailable for other purposes as a result of human use.

contagious Capable of being transmitted through direct contact. Also used to describe population distributions that are aggregated, such as in an area.

contaminative antigen Antigen borne by the parasite that is common to both the host and the parasite but that genetically is of host origin.

context In communication, stimuli other than the signal that are impinging on the receiver that might alter the meaning of a signal.

contiguity The association of events in time with particular reference here to classical conditioning.

continental boundary current A surface ocean current flowing generally north or south along a continental edge.

continental drift The breakup and movement of land masses of the earth. The earth had a single landmass about 250 million years ago. This mass broke apart into continents, which have moved slowly to their present positions.

continental margin The edge of a continent; the zone between a continent and the deep-sea floor.Also see active and passive continental margins.

continental rise The gently sloping area at the base of the continental slope.

continental shelf The shallow, gently sloping section of the continental margin that extends from the shore to the point where the slope gets steeper.

continental slope The relatively steep portion of the sea bottom between the outer edge of the continental shelf and the deep ocean basin.

continuous feeder Usually slow-moving sessile animals that feed all of the time.

continuous variable One that can assume any value whatsoever between certain limits, versus a discrete variable that can assume only specific values (usually integers).

contour feathers Feathers that cover the body, wings, and tail of a bird. Contour feathers provide flight surfaces and are responsible for plumage colors.

contour plowing Plowing along hill contours; reduces erosion.

contractile root A specialized root, common in bulbs, that contracts, pulling the stem deeper into the ground.

contractile vacuole A clear fluid-filled cell vacuole in protozoa and a few lower metazoa; takes up water and releases it to the outside in a cyclical manner, for osmoregulation and some excretion.

control That part of a scientific experiment to which the experimental variable is not applied but which is similar to the experimental group in all other respects.

control group An observed, unmanipulated set of test subjects. In an experimental manipulation, we must also perform the actions involved in that manipulation on a second test group of organisms in order to ascertain whether any effects of the experimental treatment are due to that treatment and not to the actions involved in providing the treatment.

control rods Neutron-absorbing material inserted into spaces between fuel assemblies in nuclear reactors to regulate fission reaction.

conurbation An area with more than one million people that is formed by the merger of two or more population centers and that meets other specified requirements.

convection currents Rising or sinking air currents that stir the atmosphere and transport heat from one area to another. Convection currents also occur in water; see spring overturn.

convection The act of conveying or transmission. The movement of air (or a liquid) over the surface of a body and contributes to heat loss (if the air is cooler than the body) or heat gain (if air is warmer than the body).

convective mixing The vertical mixing of water masses driven by wind stresses or density changes at the sea surface.

conventional pollutants The seven substances (sulfur dioxide, carbon monoxide, particulates, hydrocarbons, nitrogen oxides, photochemical oxidants, and lead) that make up the largest volume of air quality degradation; identified by the Clean Air Act as the most serious threat of all pollutants to human health and welfare; also called criteria pollutants.

convergent evolution Groups of unrelated organisms becoming similar in appearance because of evolutionary change in response to similar environments.

conveyor circulation See great ocean conveyor.

cool deserts Deserts such as the American Great Basin characterized by cold winters and sagebrush.

cooperation Behavior patterns that are mutually beneficial to the cooperators.

cooperative breeding A breeding system in which nonparents share in rearing the young.

copepodid Juvenile stage that succeeds the naupliar stages in copepods, often quite similar in body form to the adult.

copepods Small, mostly planktonic crustaceans.

coprolite Fossilized fecal material.

coprophagy Feeding on dung or excrement as a normal behavior among animals; reinjestion of feces.

copulation Sexual union to facilitate the reception of sperm by the female.

copy DNA See complementary DNA.

coracidium Larva with a ciliated epithelium hatching from the egg of certain cestodes; a ciliated free-swimming oncosphere.

coracoid korone = crow; oid = like.

coral knoll (pinnacle)A column of coral within the lagoon of an atoll.

coralline algae Any red alga that is impregnated with calcium carbonate. Coralline algae often contribute to coral reefs.

coralline sponges See sclerosponges.

corallite The calcareous skeletal cup in which a coral polyp sits.

coral reefs Prominent oceanic features composed of hard, limy skeletons produced by coral animals; usually formed along edges of shallow, submerged ocean banks or along shelves in warm, shallow, tropical seas.

coral rubble Coral fragments.

cord grasses Salt-tolerant grasses, species of Zostera, that inhabit salt marshes.

core The dense, intensely hot mass of molten metal, mostly iron and nickel, thousands of kilometers in diameter at the earth's center.

core area The area of heaviest use within the home range.

corepressor A substance that inhibits production of a particular enzyme.

core region The primary industrial region of a country; usually located around the capital or largest port; has both the greatest population density and the greatest economic activity of the country.

Coriolis effect The apparent change in direction of a moving object (to the left in the Southern Hemisphere and to the right in the Northern Hemisphere) due to the rotation of the earth.

corium The deep layer of the skin; dermis.

cork Suberized cells on the outer surface of woody stems and roots; produced by the cork cambium.

cork cambium Meristematic tissue that produces cork cells on its outer surface and phelloderm on its inner surface.

corm Underground, enlarged, food-storing stem covered by papery leaves.

cornea The outer transparent coat of the eye.

corneum Epithelial layer of dead, keratinized cells. Stratum corneum.

cornified Adjective for conversion of epithelial cells into nonliving, keratinized cells.

cornu Horn.

cornucopian fallacy The belief that nature is limitless in its abundance and that perpetual growth is not only possible but essential.

corolla Collective term for the petals of a flower.

corona A crown; an encircling structure. The ciliated organ at the anterior end of rotifers used for swimming or feeding.

coronary Encircling as a crown. 1. Vessels encircling the heart. 2. A condition caused by a decreased blood flow to the heart muscle. 3. Specifically, a blocked coronary artery or a branch of a coronary artery.

coronoid corona = crown; oid = like.

corpora allata Paired invertebrate endocrine glands, located in the thoracic region, which secrete juvenile hormone that prevents maturation.

corpora cardiaca Paired invertebrate endocrine glands, located near the heart, which are involved in regulation of metabolism. They receive neurosecretions from the brain and release endocrine products into the hemocoel.

corridor A strip of natural habitat that connects two adjacent nature preserves to allow migration of organisms from one place to another.

cortex The outer layer of a structure.Ground tissue located between the vascular bundles and epidermis of stems and roots.

cortisol A glucocorticoid secreted by the adrenal cortex.

cortisone An animal hormone not synthesized by plants.

cosmopolitan Worldwide in distribution.

cost/benefit analysis An evaluation of large-scale public projects by comparing the costs and benefits that accrue from them.

cost of meiosis The reduction in numbers of alleles passed on to subsequent generations as a result of reproducing sexually compared to asexually.

costa Prominent striated rod in some flagellate protozoa that courses from one of the kinetosomes along the cell surface beneath the recurrent flagellum and undulating membrane.

costal Pertaining to a rib.

cotyledon A seed leaf; the first leaf formed in a seed.

cotylocidia Larva of Aspidobothria.

counteracting osmolyte strategy An osmolyte (ion) that counteracts another ion.

countercurrent An ocean current that flows directly back into another current; also, in some animals, paired blood vessels containing blood flowing in opposite directions.

countercurrent exchange mechanism The passive exchange of something between fluids moving in opposite directions past each other.

counterillumination The emission of light by midwater animals to match the background light.

countershading Contrasting coloration that helps conceal the animal (e.g., the darkly pigmented top and lightly pigmented bottom of frog embryos).

coursers Predators that chase their prey over long distances.

courtship behavior Behavior related to the attraction of the opposite sex and mating.

covalent bond Chemical bond created by the sharing of two electrons between two atoms.

cover crops Plants, such as rye, alfalfa, or clover, that can be planted immediately after harvest to hold and protect the soil.

coxa, coxopodite The proximal joint of an insect or arachnid leg; in crustaceans, the proximal joint of the protopod.

coxae The hip.

coxal glands Excretory organs of arachnids, consisting of a sac, tubule, and opening on the coxa.

crabs Infestation with the crab louse, Phthirus pubis.

crack Form of purified cocaine with widespread street use.

Crasulacean AcidMetabolism (CAM Pathway)A variation of the C4 pathway that functions in a number of cacti and succulents; allows for the fixation of carbon dioxide during the night, then in the daytime the carbon dioxide is transferred to the Calvin Cycle.

creatine phosphate. High-energy phosphate compound found in the muscle of vertebrates and some invertebrates, used to regenerate stores of ATP.

creeping eruption Skin condition caused by hookworm larvae not able to mature in a given host.

Cremaster Suspender.

crepuscular Daily cycles with peak activity around dusk and/or dawn.

cretin A human with severe mental, somatic, and sexual retardation resulting from hypothyroidism during early stages of development.

Cribriform crib = a sieve; form = shape.

Cricoid A ring, circle.

Crinoidea The class of echinoderms whose members are attached by a stalk of ossicles or are free living. Possess a reduced central disk. Sea lilies and feather stars.

crinoids (class Crinoidea)The echinoderms with a small, cup-shaped body and feathery arms: the sea lilies and feather stars.

crista A crest or ridge on a body organ or organelle; a platelike projection formed by the inner membrane of mitochondrion.

cristae The folded-membrane inner structure of mitochondria.

criteria pollutants See conventional pollutants.

critical depth the depth at which photosynthesis equals cell respiration

critical factor The single environmental factor closest to a tolerance limit for a given species at a given time. See limiting factors.

critical period A discrete portion of a sensitive period during development, during which the probability for forming and reinforcing the behavior is greatest.

croplands Lands used to grow crops.

cropper a deep-sea animal in which the roles of predator and deposit feeder have merged

cross-pollinated Pertaining to a flower having pollen deposited on it from a different flower of another plant.

cross-pollination Transfer of pollen from the stamen to the stigma of a flower of another plant.

crossing-over The exchange of material between homologous chromosomes, during the first meiotic division, resulting in a new combination of genes.

crown The topmost portion of a plant.

crown-of-thorns sea star (Acanthaster planci)A predator of reef corals.

cruciat cruci = a cross.

crude birth rate The number of births in a year divided by the midyear population.

crude death rate The number of deaths per thousand persons in a given year; also called crude mortality rate.

crura Branches of the intestine of a flatworm.

Crural cruri = leg.

crust The cool, lightweight, outermost layer of the earth's surface that floats on the soft, pliable underlying layers; similar to the "skin" on a bowl of warm pudding.

Crustacea The subphylum of mandibulate arthropods whose members are characterized by having two pairs of antennae, one pair of mandibles, two pairs of maxillae, and biramous appendages. Crabs, crayfish, lobsters.

crustaceans (subphylum Crustacea)Arthropods that have two pairs of

cryptic coloration A color pattern that allows an organism to blend with the surroundings.

cryptobiotic Living in concealment; refers to insects and other animals that live in secluded situations, such as underground or in wood; also tardigrades and some nematodes, rotifers, and others that survive harsh environmental conditions by assuming for a time a state of very low metabolism.

cryptogonochorism Separate sexes joined or associated to form the appearance of hermaphroditism.

cryptomonads ( phylum Cryptophyta)Unicellular, eukaryotic members of the phytoplankton that have two flagella and no skeleton.

cryptoniscus Intermediate, free-swimming larval stage of the isopod suborder Epicaridea, developing after microniscus; attaches to definitive host.

cryptozoite Preerythrocytic schizont of Plasmodium spp.

crystal A solid that consists of a regular pattern of molecules.

crystalline style A proteinaceous, rodlike structure in the digestive tract of a bivalve (Mollusca) that rotates against a gastric shield and releases digestive enzymes.

crystallized song The final stage in song development, when the song variation (repertoire) has decreased and become more fixed.

ctene Bands of cilia found on the body surfaces of ctenophores.

ctenidia Comb-like structures, especially gills of molluscs; also applied to comb plates of Ctenophora.

ctenidium Series of stout, peglike spines on the head (genal ctenidium) and first thoracic tergite (pronotal ctenidium) of many fleas.

ctenoid scales Thin, overlapping dermal scales of the more advanced fishes; exposed posterior margins have fine, toothlike spines.

Ctenophora The phylum of animals whose members are characterized by biradial symmetry, diploblastic organization, colloblasts, and meridionally arranged comb rows. Comb jellies.

ctenophores See comb jellies.

Cuboid cubo = like a cube. Square.

Cuboidal cubo = a cube.

Cubozoa The class of cnidarians whose members have prominent cuboidal medusae with tentacles that hang from the corner of the medusa. Small polyp, gametes gastrodermal in origin. Chironex.

culm Hollow, jointed stem of grasses.

cultivar Abbreviation for cultivated variety of plant.

cultural eutrophication An increase in biological productivity and ecosystem succession caused by human activities.

cupula Small inverted cup-like structure housing another structure; gelatinous matrix covering hair cells in lateral line and equilibrium organs.

curare A variety of poisonous plant extracts from the bark, roots, stems, and tendrils of several woody lianas, including Chondodendron tomentosum.

currency The resource that is being maximized in an optimality model; usually assumed to be energy in an optimal foraging model.

current A horizontal movement of water.

cutaneous Pertaining to the skin (e.g., a skin infection).

cutaneous respiration Exchange of gases across thin, moist surfaces of the skin. Also cutaneous exchange or integumentary exchange.

cuticle Anoncellular, protective, organic layer secreted by the external epithelium (hypodermis) of many invertebrates; refers to the epidermis or skin in higher animals. Waterproof layer of cutin on leaves and nonwoody stems.

cuticulin Protein component of arthropod exoskeletons.

cutin Waxy material secreted by epidermal cells.

cuttings Portions of stems, usually consisting of two or three nodes, used for propagation by the production adventitious roots.

cyanobacteria (blue-green algae)The prokaryotic and generally photosynthetic organisms included in the kingdom Monera.

cyanogenic glycoside Glycoside that releases cyanide.

cyanophyte A cyanobacterium, blue-green alga.

cycads Members of the Cycadophyta, which have unbranched stems and a terminal grouping of leathery, compound leaves.

cycle Repeating units that make up the pattern of biological rhythms.

cyclic photophosphorylation The formation of ATP by activation of PS I, but failure to activate PS II. Consequently ATP is formed, but NADP is not reduced.

cyclin. A protein important in the control of the cell division cycle and mitosis.

cycloid scales Thin, overlapping dermal scales of the more primitive fishes; posterior margins are smooth.

cyclosis The spontaneous movement of cytoplasm and some organelles within the cell.

cydippid larva Free-swimming larva of most ctenophores; superficially similar to the adult.

cynodonts A group of mammal-like carnivorous synapsids of the Upper Permian and Triassic.

cypris Postnaupliar larva of barnacles (crustacean subclass Cirripedia) in which the carapace largely envelops the body; so called because of its resemblance to the ostracod genus Cypris.

cyrtocyte A protonephridial cell with a single flagellum enclosed in a cylinder of cytoplasmic rods.

cyst A secreted covering that protects many small invertebrates, including some protozoans, rotifers, and nematodes, from environmental stresses, such as desiccation and overcrowding.In diatoms, a resistant and photosynthetically inactive cell.

cystacanth Juvenile stage of an acanthocephalan that is infective to the definitive host.

Cystic kystis = a sack or pouch.

cysticercoid A type of juvenile tapeworm composed of a solid-bodied cyst containing an invaginated scolex; contrast with cysticercus.

cysticercosis Infection with the larval forms (Cysticercus cellulosae) of Taenia solium.

cysticercus Metacestode developing from the oncosphere in most Cyclophyllidea; usually has a tail and a well-formed scolex and characterized by a fluid-filled oval body with an invaginated scolex; cysticercoid.

cystid In an ectoproct, the dead secreted outer parts plus the adherent underlying living layers.

cystogenic cells Secretory cells in a cercaria that produce a metacercarial cyst.

cytochrome Several iron-containing pigments that serve as electron carriers in aerobic respiration.

cytokine A molecule secreted by an activated or stimulated cell, for example, macrophages, that causes physiological changes in certain other cells.

cytokinesis The division of the cytoplasm of a cell into two parts, as distinct from the division of the nucleus (which is mitosis).

cytokinin A group of hormones that promote growth by stimulating cell division.

cyton Cell body; contains nucleus and some other organelles but excludes processes extending from cell. For example, the neurocyton is the nerve cell body, excluding the axon and dendrites.

cytophaneres Fibers radiating out from a zoitocyst into surrounding muscle; found in some species of Sarcocystidae.

cytopharynx A region of the plasma membrane and cytoplasm of some ciliated and flagellated protists specialized for endocytosis. A permanent oral canal.

cytoplasm The living matter of the cell, excluding the nucleus.

cytoplasmic inclusion The basic food material or stored product of a cell's metabolic activities.

cytoproct Site on a protozoan where undigestible matter is expelled.

cytopyge A region of the plasma membrane and cytoplasm of some ciliated protists specialized for exocytosis of undigested wastes.

cytosine A nitrogen base found in both DNA and RNA.

cytoskeleton In the cytoplasm of eukaryotic cells, an internal framework of microtubules, microfilaments, and intermediate filaments by which organelles and other structures are anchored, organized, and moved about.

cytosol Contents of the main compartment of the cytoplasm, excluding membrane-bound organelles.

cytosome The cell body inside the plasma membrane.

cytotoxic T cells A special T cell activated during cell-mediated immune responses that recognizes and destroys virus-infected cells.