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Key Words Final Exam Bio 1130

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Bio1130- Organismal Biology Key Words: Final Exam Cambrian and Ordivician: Acoelomate: Describing any bilaterally symmetrical animal of the subkingdom Eumetazoa that does not possess a coelom. Examples of acoelomate animals are the platyhelminths. Algal Mats: a layer of usually filamentous algae on marine or fresh water soft bottoms. It may be considered one of many types of microbial mats. Amoebocyte: an animal cel whose location is not fixed and is therefore able to wander through the body tissues. Amoebocytes are named after their resemblance, especially in their movement, to Amoeba and they feed on foreign partices (including invading bacteria). They occur, for example, in sponges and mammalian blood. (eg some leukocytes) Archenteron: a cavity within an animal embryo at the gastrula stage of development. All or part of the archenteron eventually forms the cavity of the gut. It is connected to the outside by an opening (the blastopore), which becomes either the mouth, the mouth and anus or the anal opening of the animal. Archeocyte: Archaeocytes or amoebocytes are amoeboid cells found in sponges. They are totipotent and have varied functions depending on the species. Assymetric Body Plan: Assymetrical animals (sponges) have no general body plan or axis of symmetry that divides the body into mirror image halves. Within the animal kingdom this appears to be a primitive condition. Bilateral Symmetry Body Plan: A basic body plan in which the left and right sides of the organism can be divided into approximate mirror images of each other along the midline. Bivalvia: A class of aquatic molluscs (the bivalves) that inclue the oysters, mussels and clams. They are characterized by a laterally flattened body and a shell consisting of two hinged shells (ie. a bivalve shell). The enlarged gills are covered with cilia and have the additional function of filtering microscopic food particles from the water flowing over them. Bivavles live on the sea bed or lake bottom and are sedentary, so the head and foot are reduced. Blastopore: a Blastopore is an opening into the archenteron during the embryonic stages of an organism. The distinction between protostomes and deuterostomes is based on the direction in which the mouth develops in relation to the blastopore. Blastula: The stage of development of an animal embryo that results from cleavage of a fertilized egg. This stage generally resembles a hollow ball with the dividing cells (blastomeres) of the embryo forming a layer (blastoderm) around a central cavity (blastocoel). In vertebrates the blastula forms a disc (blastodisc) on the surface of the yolk. In mammals, the blastula stage is known as a blastocyst. Bryozoa: A phylum of aquatic, mainly marine, invertebrates comprising the moss animals and sea mats. Bryozoans live in colonies, 50 cm or more across, which are attached to rocks, seaweeds or shells. The individuals (zooids) making up the colonies are about 1mm long and superficially resemble cnidarian polyps, with a mouth surrounded by ciliated tentacles of the lophophore that trap minute particles of organic matter in the water. Some have a horny or calcareous outer skeleton into which the body can be withdrawn. Bryozoans are placed in the clade of protostome animals called the Lophotrochozoa. Burgess Shale Fossils: A rock formation in the western Canadian Rockies containing a wealth of fossilized invertebrates of the early Cambrian Period that were buried by an underwater avalanche of fine silt, preserving many details of their soft parts and providing valuable information about the evolution of early life. Cambrian: The earliest geological period of the Paleozoic era. It is estimated to have begun about 542 million years ago and lasted for some 54 million years. During this period marine animals with mineralized shells made their first appearance and Cambrian rocks are the first to contain an abundance of fossils. Cambrian fossils are chiefly of marine animals; they include trilobites, which dominated the Cambrian seas, echinoderms, brachiopods, molluscs, and primitive graptolites (from the Mid Cambrian). Trace fossils also provide evidence for a variety of worms. Cambrian Explosion: A relatively short interval of rapid intense evolution that supposedly occurred in the early to mid-Cambrian period, some 540 to 520 millions years ago. The supposition is based on the sudden appearance in the fossil record from this times of many diverse and novel forms, particularly marine animals, among which can be found representatives of all major modern groups. Notable well-preserved fossil assemblages dating to this period include the Burgess Shale fossils of Canada and the Chengjiang fossils of China. There is debate about whether such an explosion actually occurred or whether the evidence supporting it merely reflects discontinuity in the fossil record—that is, Precambrian ancestors of these fossil specimens did exist but were simply not fossilized. Carnivores: An animal that eats meat, especially a member of the order Carnivora. Carnivores are specialized by having strong powerful jaws and well-developed canine teeth. They may be predators or carrion eaters. Cephalization: the tendency among animal groups for the major sense organs, mouth and brain to be grouped together at the front end of the body. These are usually contained in a specialized cephalic region- the head. Cephalopoda: The most advanced class of molluscs, containing the squids, cuttlefishes, octopuses and the extinct ammonites. Cephalopods have a highly concentrated CNS within a protective cartilaginous case. The eye has a well developed retina and is comparable to that of vertebrates. All cephalopods are predacious carnivores capable of swimming by jet propulsion; they have highly mobile tentacles for catching and holding prey. Choanocyte: A flagellated cell with a collar of protoplasm at the base of the flagellum, numbers of which line the internal chambers of sponges. Choanoderm: composed of flagellated collar cells, or choanocytes. The sponge body is mostly a connective tissue, the mesohyl, over which are applied epithelioid monolayers of cells, the outer pinacoderm and the inner choanoderm. Most aspects of sponge biology, including feeding, reproduction, and gas exchange, depend on a low pressure flow of water generated by the flagella of the choanoderm. Cnidaria: A phylum of aquatic invertebrates (sometimes known as coelenterates) that includes Hydra, jellyfish, sea anemones, and corals. A cnidarians body is diploblastic with two cell layers of the body wall separated by mesoglea, and shows radial symmetry. The body cavity (gastrovascular cavity) is sac-shaped, with one opening acting as both mouth and anus. This opening is surrounded by tentacles bearing thread cells. Cnidarians exist both as free swimming medusa (ex jellyfish) and as sedentary polyps. The latter may be colonial (ex corals) or solitary (ex sea anemones and Hydra). In many cnidarians the life cycle alternates between these two forms. The phylum contains the classes of Hydrozoa, most members of which show alternation of generations; Scyphozoa (jellyfish) in which the medusa phase is dominant; and Anthozoa (corals and sea anemones) in which medusae are absent. Cnidocil: A minute process of a nematocyst that when touched is believed to cause the projection of the stinging thread. (jellyfish) Cnidocyte: A capsule, in certain cnidarians, containing a barbed, threadlike tube that delivers a paralyzing sting. Coelom Formation: A fluid filled body cavity which is formed from the splitting of lateral plate mesoderm during embryonic development. Coelomate: animals that have a coelom Colonial Choanoflagellate: the series used to describe developmental stages of the parasitic flagellates, denoting the barleycom form of the flagellate in the genus crithidia characterized by a collarlike extension surrounding the anterior and through which the single flagellum emerges. Corals: Any of a group of sedentary colonial marine invertebrates belonging to the class Anthozoa of the phylum Cnidaria. A coral colony consists of individual polyps within a protective skeleton that they secret: this skeleton may be soft and jelly like, horny or stony. The horny skeleton secreted by corals of the genus Corallium especially C. rubrum, constitutes the red, or precious coral used as a gemstone. The skeleton of a stony, or true corals consists of almost pure calcium carbonate and forms the coral reefs common in tropical seas. Deposit (Substrate) Feeders: Any animal that feeds on the detritus that collects on the substratum at the bottom of water. Also known as detritus feeder. Deuterosome: an animal in which the opening (blastopore) of the embryonic cavity becomes the anus and the mouth forms as a secondary orifice. The name derives from Greek, meaning literally “second mouth”. Deuterostomes comprise one of the two main subkingdoms of animals (Deuterostomia), the other being the Protostomia. Deuterostomes typically display radial cleavage of the blastula, indeterminate developing (ie by outpocketing of the embryonic gut). The three deuterostome phyla are the Hemichordata, Echindodermata and Chordata. Diploblastic: Describing an animal with a body wall composed of only two layers, ectoderm and endoderm, sometimes with a noncellular mesoglea between them. Coelenterates (ie cnidarians and ctenophorans) are diploblastic. Doushantuo Fossils: aquatic, microscopic, and preserved to a great degree of detail. The latter two characteristics mean that the structure of the organisms that made them can be studied at the cellular level, and considerable insight has been gained into the embryonic and larval stages of many early creatures. Ecdysis: The periodic loss of the outer cuticle of arthtropods. It starts with the reabsorption of some materials in the inner part of the old cuticle and the formation of a new soft cuticle. The remains of the old cuticle then split; the animal emerges and absorbs water or swallows air and increases in size while the new cuticle is still soft. This cuticle is then hardened with chitin and lime salts. In insects and crustaceans ecdysis is controlled by the hormone ecdysone. Ecdysozoa: A clade of protostome animals, based chiefly on molecular systematics, whose members include the arthropods, nematodes, onychophorans, and tardigrades. All are characterized by their habit of periodic moulting (i.e. ecdysis, hence the name of the clade). Ectoderm: The external layer of cells of the gastrula, which will develop into the epidermis and the nervous system in the adult. Ediacaran Fossils: Relating to a group of fossilized organisms that are the earliest known remains of multicellular life. They are soft-bodied marine life forms that date from between 560 and 545 million years ago, during the late Precambrian Eon. Ediacaran Period: a late Precambrian period of geological time, before the Cambrian Period to 635 million years ago; also, the last faunal stage of the Precambrian or Proterozoic End Ordovician Extinction: The End–Ordovician extinction event is the third- largest extinction event of the Phanerozoic era. The Ordovician period followed the Cambrian and was followed by the Silurian. There were no living things on the land except for bacteria and perhaps some single-celled algae. The biota was almost entirely marine. The extinction came in two steps, at the start and the finish of the Hirnantian stage, which was the last stage of the Ordovician. 1. Pre-event: warm climate, deep ocean anoxic event. ocean bottoms were anoxic (little or no oxygen). Black shales were laid down in deep ocean strata; carbonates laid down on oxygenated continental shelves. 2. First step: climate turns cold; turnover of water in seas. Rising anoxic water kills most of the plankton, and shrinking seas remove habitats. Cold stage with clear evidence of widespread glaciation. 4. Second step: warming ocean re-established; glaciers melt, anoxic conditions reach continental shelves and kills fauna again. Basic mechanism: climate changes from very warm to very cold and back to very warm. Changes in ocean circulation were the results of the climate changes. Both benthic (ocean bottom) and pelagic fauna were faced with conditions they were unable to cope with. More than 100 invertebrate families becam extinct in the End– Ordovician extinction event, and a total of almost half the genera.[4] The brachiopods and bryozoans were decimated, along with many of the trilobite, conodont and graptolite families. Endoderm: The internal layer of cells of the gastrula, which will develop into the alimentary canal (gut) and digestive glands of the adult. Endoparasites: A parasite that lives inside its host's body Enterocoel: a coelom or coelomic cavity, present in some invertebrates, which has developed from the wall of the archenteron. Epidermis: 1 (in zoology) The outermost layer of cells of the body of an animal. In invertebrates the epidermis is normally only one cell thick and is covered by an impermeable cuticle. In vertebrates the epidermis is the thinner of the two layers of skin (compare dermis). It consists of a basal layer of actively dividing cells (see Malpighian layer), covered by layers of cells that become impregnated with keratin (see keratinization). The outermost layers of epidermal cells (the stratum corneum) form a water-resistant protective layer. The epidermis may bear a variety of specialized structures (e.g. feathers, hairs). 2 (in botany) The outermost layer of cells covering a plant. It is overlaid by a cuticle and its functions are principally to protect the plant from injury and to reduce water loss. Some epidermal cells are modified to form guard cells (see stoma) or hairs of various types (see piliferous layer). In woody plants the functions of the shoot epidermis are taken over by the periderm tissues (see cork cambium) and in mature roots the epidermis is sloughed off and replaced by the hypodermis. Epitheliomusculature: of or being an epithelial cell of coelenterates that is modified to function in contraction and has an elongated fibrillar base that functions in the same manner as a muscle cell Filter Feeder: An aquatic animal, such as a clam, barnacle, or sponge, that feeds by filtering particulate organic material from water. Gap Junctions: A passage through the lipid bilayers of adjacent plasma membranes that mediates the transfer of small molecules or ions between interacting cells. Gap junctions are abundant in epithelial tissues and cardiac muscle. They consist of hexagonally packed tubes (connexons), approximately 10 nm in diameter, through which small molecules or ions may directly pass from the interior of one cell to the interior of the other. Gap junctions, together with chemical synapses (which function through neurotransmitters), are communicating junctions and comprise one of several types of cell junction. Gastrodermis: The epithelial lining of the digestive tract of certain invertebrates, including the nematode worms and coelenterates. Gastropod: A class of molluscs that includes the snails, whelks, limpets, land and sea slugs, and conches. Molluscs have a well-developed head with tentacles, a large flattened foot, and a coiled twisted shell. They occupy marine, freshwater, and terrestrial habitats; in the terrestrial and some freshwater gastropods the mantle cavity acts as a lung instead of enclosing gills. Gastrozooid: zooids in colonies of Coelenterates (hydropolyps, hydrocorals, and Siphonophores) that carry out the digestive function. They resemble polyps with partially or completely atrophied tentacles. Located nearby or at the base of the gastrozooid are zooids adapted for capturing prey (dactylozooids, stinging tentacles) and which transfer their prey to the gastrozooid for digestion. Gastrula: The stage in the development of an animal embryo that succeeds the blastula. It begins with the production of the primary germ layers and the embryo becomes converted to a cup-shaped structure containing a cavity (the archenteron). Gastrulation: (Science: embryology) During embryonic development of most animals a complex and co-ordinated series of cellular movements occurs at the end of cleavage. The details of these movements, gastrulation, vary from species to species, but usually result in the formation of the three primary germ layers, ectoderm, mesoderm and endoderm. Gonozooid: A sexual zooid, or medusoid bud of a hydroid; a gonophore. See Hydroidea, and Illust. of Campanularian. Herbivores: An animal that eats vegetation, especially any of the plant-eating mammals, such as ungulates (cows, horses, etc.). Herbivores are characterized by having teeth adapted for grinding plants and alimentary canals specialized for digesting cellulose Hermaphrodite: An animal, such as the earthworm, that has both male and female reproductive organs. Homeotic Genes: A developmental gene that specifies the anterior-posterior axis, as well as segment identity during the early embryonic development of certain organisms, such as metazoans. Homeotic Mutants: a mutation that causes tissues to alter their normal differentiation pattern, producing integrated structures but in unusual locations. For example, a homeotic mutation in the fruit fly, Drosphila, causes legs to develop where antennae normally form. Hox Genes: A class of homeotic genes that control development of structures along the head-to-tail (anteroposterior) axis of a wide range of animals. The Hox genes are organized into clusters on certain chromosomes; jawed vertebrates, for example, have four Hox gene clusters. In mammals these four clusters are designated Hox A, Hox B, Hox C, and Hox D, each on a separate chromosome, with individual genes given numbers, hence, A1, A2, B1, B2, etc. Nematodes, arthropods, and cephalochordates have a single cluster. Hox genes are highly conserved, showing remarkable similarity of DNA sequence and function; each falls into one of several groups of paralogous genes, derived by duplication of ancestral genes. Moreover, in embryos of all animals studied, the Hox genes show colinearity – their sequence of expression in body segments from head to tail reflects their linear arrangement in the homeotic gene clusters. Hydrostatic Skeleton: The system of support found in soft-bodied invertebrates, which relies on the incompressibility of fluids contained within the body cavity. For example, in earthworms the coelomic fluid is under pressure within the coelom and therefore provides support for internal organs. Ingestive Heterotroph: Organisms that consume food and digest it inside their bodies. Lophophore: An organ characteristic of aquatic invertebrates of the phyla Bryozoa, Phoronida, and Brachiopoda that functions in filter feeding. It consists of a ridge of hollow tentacles bearing cilia, which waft food particles into the mouth. Lophotrochozoa: A clade of protostome animals, based on molecular systematics, that includes the molluscs and annelid worms, together with the nemertines, bryozoans, and other wormlike phyla. Mantle: The fold of skin covering the dorsal surface of the body of molluscs, which extends into lateral flaps that protect the gills in the mantle cavity (the space between the body and mantle). The outer surface of the mantle secretes the shell (in species that have shells). Medusa: The free-swimming stage in the life cycle of the Cnidaria. Medusae are umbrella-shaped, with tentacles round the edge and the mouth in the centre underneath. They swim by pulsations of the body and reproduce sexually. In the Hydrozoa (e.g. Hydra) they alternate in the life cycle with polyps, from which they are produced by budding. In the Scyphozoa, which includes all the common jellyfish, the medusa is the dominant form and the polyp is reduced or absent. Mesoderm: The layer of cells in the gastrula that lies between the ectoderm and endoderm. It develops into the muscles, circulatory system, and sex organs and in vertebrates also into the excretory system and skeleton. Mesoglea: The gelatinous noncellular layer between the endoderm and ectoderm in the body wall of coelenterates. It may be thin, as in Hydra, or tough and fibrous, as in the larger jellyfish and sea anemones. It often contains cells that have migrated from the two body layers but these do not form tissues and organs and the mesoglea is not homologous with the mesoderm of triploblastic animals. Metamerization: the formation or differentiation of metameres Mollusc: A phylum of soft-bodied invertebrates characterized by an unsegmented body differentiated into a head, a ventral muscular foot used in locomotion, and a dorsal visceral hump covered by a fold of skin – the mantle – which secretes a protective shell in many species. Respiration is by means of gills (ctenidia) or a lunglike organ and the feeding organ is a radula. Molluscs occur in marine, freshwater, and terrestrial habitats and there are six classes, including the Gastropoda (snails, slugs, limpets, etc.), Bivalvia (bivalves, e.g. mussels, oysters), and Cephalopoda (squids and octopuses). Omnivores: An animal that eats both animal and vegetable matter. Pigs, for example, are omnivorous. Onycophora: A small phylum of caterpillar-like invertebrates – the velvet worms – that inhabit moist dark terrestrial habitats, such as forest litter and caves, in tropical and warm regions. The thin chitinous cuticle, which bears numerous papillae and sensory hairs giving it a velvety feel, is periodically moulted. The 110 or so known species, which include Peripatus, are generally small, with brownish bodies, although some are more brightly coloured. Sizes range from 14 mm to 200 mm in length, with females larger than males, and there may be from 14 to more than 40 pairs of unjointed hollow legs. Onychophorans capture prey, such as spiders and termites, by entangling them in a sticky secretion squirted from adhesive glands opening beside the mouth. The sexes are separate; some species lay eggs, whereas others are ovoviviparous or viviparous, the latter nourishing embryos internally via a placenta analogous to that of mammals. Onychophorans are closely related to arthropods and are thought to have descended from extinct marine forms that flourished in the Cambrian, such as Aysheaia and Hallucigenia, found in the Burgess shale deposits. Such fossil forms are now sometimes placed with modern velvet worms in the phylum Lobopodia. Ootype: The production and growth of the ova (egg cells) in the animal ovary. Special cells (oogonia) within the ovary divide repeatedly by mitosis to produce large numbers of prospective egg cells ( primary oocytes). When mature, these undergo meiosis, which halves the number of chromosomes. During the first meiotic division a polar body and a secondary oocyte are produced. At the second meiotic division the secondary oocyte produces an ovum and a second polar body. Oocytes may be present in the ovaries at birth and may represent the total number of eggs to be produced. Ordovician Period: The second geological period of the Palaeozoic era, following the Cambrian and preceding the Silurian periods. It began about 488 million years ago and lasted for about 44 million years. The period was named by the British geologist Charles Lapworth (1842–1920) in 1879. Graptolites, in deep-water deposits, are the dominant fossils. Other fossils include trilobites, brachiopods, ectoprocts, gastropods, bivalves, echinoids, crinoids, nautiloid cephalopods, and the first corals. Pentaramous Symmetry: Pentamerous radial symmetry describes an animal whose body can be divided into five parts that point outward from the center of the body. For example, sea stars, urchins, and brittle stars exhibit pentamerous radial symmetry. Pinacoderm: The pinacoderm is the outer most layer of cells in the phylum Porifera, equivalent to the epidermis in other organisms. The pinacocytes are on the external surface of the sponge body and characterized as an epithelial layer of flattened cells. Platyzoa: A clade of protostome animals based on molecular systematics and including the flatworms, rotifers, and certain other phyla. Platyhelminthes: A phylum of acoelomate invertebrates comprising the flatworms, characterized by a flattened unsegmented body. The simple nervous system shows some concentration of cells at the head end. The mouth leads to a simple branched gut without an anus. Flatworms are hermaphrodite but self-fertilization is unusual. Many species are parasitic. The phylum contains the classes Turbellaria (planarians), Trematoda (flukes), and Cestoda (tapeworms). Molecular evidence now suggests that the majority of flatworms are secondarily acoelomate and belong to the Platyzoa. This distinguishes them from those platyhelminths traditionally placed in the order Acoelomorpha, which are primitively acoelomate and descended from an ancient animal lineage that is neither protostome nor deuterostome Polyp: The sedentary stage in the life cycle of the Cnidaria, consisting of a cylindrical body fixed at one end to a firm base and having a mouth surrounded by a ring of tentacles at the other. Some polyps (e.g. Hydra) are single; others (e.g. the corals and Obelia) form colonies. Polyps typically reproduce asexually by budding to form either new polyps or medusae. The latter reproduce sexually giving rise to new polyps. Sea anemones are solitary polyps that reproduce sexually to form new polyps. Porifera: The phylum of marine and freshwater invertebrates that comprise the sponges, which live permanently attached to rocks or other surfaces. The body of a sponge is hollow and consists basically of an aggregation of cells between which there is little nervous coordination. The body is supported by an internal skeleton of spicules of chalk, silica, or fibrous protein (bath sponges have protein skeletons). Undulipodium-bearing (flagellated) cells (choanocytes) cause water to flow in through openings ( ostia) in the body wall and out through openings ( oscula) at the top; food particles are filtered from the water by the choanocytes. Predators: An animal that obtains its food by predation. All predators are carnivores, although not all carnivores are predators. Protostome: An animal in which the mouth develops from the opening (blastopore) of the embryonic cavity (see archenteron). The name derives from Greek, meaning literally ‘first mouth’. Protostomes constitute one of the two major subkingdoms of animals (Protostomia), the other being the Deuterostomia (see deuterostome). Other features typical of protostomes are spiral cleavage of the blastula, determinate development (i.e. the fate of cells is established at a very early embryonic stage), and schizocoelic formation of a coelom where one occurs (i.e. by formation of a cavity within a solid mass of mesoderm). Three main clades of protostomes are now recognized: Ecdysozoa; Lophotrochozoa; and Platyzoa. Pseudocoelomate: Describing any invertebrate animal whose body cavity is a pseudocoel, a cavity between the gut and the outer body wall derived from a persistent blastocoel (see blastula), rather than a true coelom. Pseudocoelomate animals include the Rotifera and Nematoda. Radial Cleavage: holoblastic cleavage that is typical of deuterostomes and that is characterized by arrangement of the blastomeres of each upper tier directly over those of the next lower tier resulting in radial symmetry around the pole to pole axis of the embryo — compare spiral cleavage Radial Symmetry Body Plan: a basic body plan in which the organism can be divided into similar halves by passing a plane at any angle along a central axis, characteristic of sessile and bottom-dwelling animals, as the sea anemone and starfish. Radula: A tonguelike organ of molluscs, consisting of a horny strip whose surface is studded with rows of horny teeth for rasping food. In some species it is modified for scraping or boring. Reefs: a ridge of jagged rock, coral, or sand just above or below the surface of the sea. Schizocoel: a perivisceral cavity that arises by the splitting of the mesoblast of the embryo Seminal Receptacle: Receives sperm from another worm Seminal Vesicle: A pouch or sac in many male invertebrates and lower vertebrates that is used for storing sperm. Setae: A bristle or hair in many invertebrates. Setae are produced by the epidermis and consist either of a hollow projection of cuticle containing all or part of an epidermal cell (as in insects) or are composed of chitin (as in the chaetae of annelid worms). Slushball Earth: The “Slushball Earth” hypothesis, developed by American geologist Richard Cowen, contends that Earth was not completely frozen over during periods of extreme glaciation in Precambrian times. Rather, in addition to massive ice sheets covering the continents, parts of the planet (especially ocean areas near the Equator) could have been draped only by a thin, watery layer of ice amid areas of open sea. Under this scenario, photosynthetic organisms in low-ice or ice-free regions could continue to capture sunlight efficiently and survive long periods of extreme cold. Snowball Earth: Snowball Earth hypothesis, in geology and climatology, an explanation first proposed by American geobiologist J.L. Kirschvink suggesting that Earth’s oceans and land surfaces were covered by ice from the poles to the Equator during at least two extreme cooling events between 2.4 billion and 580 million years ago. Spiral Cleavage: holoblastic cleavage that is typical of protostomes and that is characterized by arrangement of the blastomeres of each upper tier over the cell junctions of the next lower tier so that the blastomeres spiral around the pole to pole axis of the embryo Sponges: The phylum of marine and freshwater invertebrates that comprise the sponges, which live permanently attached to rocks or other surfaces. The body of a sponge is hollow and consists basically of an aggregation of cells between which there is little nervous coordination. The body is supported by an internal skeleton of spicules of chalk, silica, or fibrous protein (bath sponges have protein skeletons). Undulipodium-bearing (flagellated) cells (choanocytes) cause water to flow in through openings ( ostia) in the body wall and out through openings ( oscula) at the top; food particles are filtered from the water by the choanocytes. Spongocoel: The central cavity of a sponge, which opens to the outside by way of the osculum Suspension Feeders: an aquatic animal which feeds on particles of organic matter suspended in the water, especially a bottom-dwelling filter feeder. Tagma: A section of the body of an arthropod that is formed by the fusion of mesodermal somites and has a distinct function and structure. The basic tagmata are the head, thorax, and abdomen, but the form of the tagmata (known as tagmosis) varies between arthropod groups, each group having its characteristic tagmosis. For example, many crustaceans have a cephalothorax and abdomen, while arachnids have a prosoma and opisthosoma. Totipotent Cells: A cell that can give rise to the entire organism, including the extra- embryonic membranes; the fertilized egg or zygote is totipotent. Triploblastic: Describing an animal having a body composed of three embryonic cell layers: the ectoderm, mesoderm, and endoderm. Most multicellular animals are triploblastic; the coelenterates, which are diploblastic, are an exception. Trochophore: The pelagic planktonic larva of polychaete worms, some molluscs, and certain other invertebrates. It is top-shaped and usually has two bands of cilia encircling the body. Tube Feet: A phylum of marine invertebrates that includes the sea urchins, starfish, brittlestars, and sea cucumbers. Echinoderms have an exoskeleton (test) of calcareous plates embedded in the skin. In many species (e.g. sea urchins) spines protrude from the test. A system of water-filled canals (the water vascular system) provides hydraulic power for thousands of tube feet: saclike protrusions of the body wall used for locomotion, feeding, and respiration. Echinoderms have a long history: fossils of primitive echinoderms are known from rocks over 500 million years old. Like chordates, they are deuterostomes. Extant classes include the Crinoidea (sea lilies), Holothuroidea (sea cucumbers), Echinoidea (sea urchins), and Stelleroidea (starfish and brittlestars). Silurian and Deconian: Actinopterygii: also known as ray-finned fishes, constitute a subclass of the bony fishes. They are called ray-finned because they possess “fin rays”, their fins being webs of skin supported by bony or horny spines, as opposed to the fleshy, lobed fins that characterize the class Sarcopterygii which also, however, possess lepidotrichia. Agnatha: Any jawless craniate animal. Agnathans were formerly classified in the subphylum (or superclass) Agnatha, with the living representatives. (ex lamprey) Alternation of Generations: The occurrence in one life history of two or more different forms differently produced, usually an alternation of a sexual with an asexual form. The alternation of two or more different forms in the life cycle of a plant or animal. A unique occurrence where one generation reproduces sexually then the next reproduces asexually. Antheridia: The male sex organ of algae, mosses, ferns, fungi and other non flowering plants. Archegonia: The female sex organ in mosses, liverworts, ferns, and most conifers. Arthropoda: A large phylum of invertebrate animals that includes insects, spiders, crustaceans, and their relatives. They have a segmented body, an external skeleton, and jointed limbs, and are sometimes placed in a different phyla. Bony Fish: A fish of a large class distinguished by a skeleton bone, and comprising the majority of modern fishes. Cartilagenous Fish: A fish of a class distinguished by having a skeleton of cartilage rather than bone, including the sharks, rays and chimaeras. Chondricthyes: Jawed fish with paired fins, paired nares, scales, a heart with it’s chambers in series and skeletons made of cartilage rather than bone. Crustacean: form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. Devonian Period: “The age of Fishes”; Fourth of six periods that make up the Paleozoic Era. During this period fish such as agnanthans and placoderms attained their highest levels of diversity. Additionally, true bony fishes and cartilaginous fishes first appeared and both groups are thought to have evolved from the placoderms. External Fertilization: External fertilization is a strategy of fertilization in which a sperm cell unites with an egg cell in the open, rather than inside specialized organs within the bodies of the parents. Gametangia: a gamentangium is an organ or cell in which gametes are produced that is found in many multicellular protists, algae, fungi and the gametophytes of plants. Gametophyte: a gametophyte is a haploid multicellular adult stage in the alternation of generations during the life cycle of land plants and algae. It produces haploid gametes. Gastropod: The gastropoda or gastropods, more commonly known as snails and slugs, are a large taxonomic class within the Phylum Mollusca. The class Gastropoda includes snails and slugs of all kinds and all sizes from microscopic to large. Gemma and Gemma Cups: Gemma: a small cellular body or bud that can separate to form a new organism; Gemma cups: Part of a plant that appears as a cup like structure located on its surface. Gemma cups are common in asexual plants as this is their mode of reproduction. The gemma cups contain the reproductive cells called gemma which detages from the parent plants then buds after it has fragmented on the ground. Gill Arches: One of several bony or cartilaginous arches located on either side of the pharynx and supporting the gills in fish and amphibians. Gill Slits: One of several narrow external openings connecting with the pharynx, characteristic of sharks and related fishes, through which water passes to the exterior, thereby bathing the gills; One of the several rudimentary invaginations in the surface of the embryo, present during development of all air breathing vertebrates and corresponding to the functional gill slits of aquatic species. Gnathostomes: Gnathostomata are the jawed vertebrates. The term derives from Greek “jaw” and “mouth”, and it includes all vertebrates except the agnathans. Heterocercal Tail: (of a fishes tail) having unequal upper and lower lobes
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