Animal Evolution

Animal Evolution

Poriferasponges • 5,000 living sponge species • Three Main Groups: • hexactineuida (glass sponges) • demospangia • calcarea (calcareous sponges) • no coelom, organs, or skeleton • no urinary, cardiovascular, respiratory or nervous system • cellular grade of organization

Evolutionary Time Frame • Among the oldest known fossils • began in late Precambrian • developed from first multi-cellular organism

Tissues • Two layers of cells • layers are separated by gelatinous region called mesohyl • Spongocoel • the central cavity • internal water chambers • water flows in and out of the osculum • coanocytes are flagellated, collar cells • these line the spongocoel • help propel water through cell

Reproduction • Reproduce sexually or asexually • Hermaphrodites • this means they are male and female • produce both eggs and sperm • gametes arise from choanocytes or amoebocytes • eggs reside in the mesohyl, while sperm cells are carried out of the sponge by water current • fertilization occurs in the mesohyl • zygotes develop into flagellated, swimming larvae • in asexual reproduction buds are produced • are often packets of several cells inside a protective coating called gemmule

Locomotion • No muscles

Digestion • No mouths • carnivores • archaiout, cells ingest and digest food • suspension feeders • “filter feeders” • they collect bacteria taken from the water • tiny pores in outer walls • these draw water • called ostia • cells in sponge walls filter water • water is pumped through the body and out larger opening (oscula) • flow of water is unidirectional • driven by beating of flagella which line the surface of chambers and are connected by a series of canals

Cnidariacorals, jellyfish, hydra • Four Main Classes • Anthozoa (corals, anemones, sea pens, sea fans, sea anemones) • Cubozoa (box jellies) • Hydrozoa (diverse group of siphonophores, hydroids, five corals, medusae, obella) • Scyphozoa (true jellyfish, jellies, sea wasps, sea nettles) • do not have a cardiovascular system

Evolutionary Time Frame Cnidaria first appeared during the Pre-Cambrian era • Corals - first appeared in Vendian • few fossils in Cambrian period, but identifiable corals began evolutionary radiation in Early Ordovician Period • wiped out at end of Permian Period • mass extinction event in which 95% of all marine invertebrate species became extinct • scleractinian corals appeared in the middle of the Triassic (15 million years later) • became dominant hermatypic (reef-building) organisms in shallow tropical marine habitats

Tissues • Simplest organisms at tissue level • cells are organized in true tissues • two cell layers - outer ectoderm (epidermis) and inner endoderm (gastrodermis) • Outer Ectoderm • contains cnidocysts (stinging cells) • Inner Endoderm • lines gut (sometimes divided by septa) • Mesoglea (between layers) • layer of jelly-like substance • contains scattered cells and collagen fibers

Excretion • Cnidarias have one oral opening • all secretions, including waste materials, exit through this • Undigested remains are sent back through the anus/mouth

Reproduction • Alternate between asexual and sexual • sexual reproduction includes free-swimming forms • formation of gametes in medusae and some polyps • asexual budding (polyps) • Gonads are the only organs present in the body cavity of cnidaria

Locomotion • Cnidaria move by a decentralized nerve net and simple receptors • movement is coordinated by the nerve net • move freely in water by passive drifting and contractions of its bell-shaped body

Digestion • Cnidaria are carnivores • they have tentacles in a ring around their mouth • these capture prey and push food into the gastrovascular cavity • gastrovascular cavity is a sac with a central digestive compartment • cnidaria have one opening which functions as the mouth and anus

Respiratory • Done by the diffusion of oxygen through their tissues

Nervous • Cnidaria contain muscles and nerves in the simplest form • Cells of the epidermis and gastrodermis have bundles of microfilaments arranged in contractile fibers • there is no brain, and the nerve net is associated with simple sensory receptors that are distributed throughout the body

Platyhelminthesflat worms • Means “flat worm” • thin bodies between dorsal and ventral surfaces • Consist of Four Classes: • Turbellaria (free-living flatworms) • Monogenea (monogeneans) • Trematoda (trematodes or flukes) • Cestoidea (tapeworms) • no urinary system

Evolutionary Time Frame • Origin of bilaterians, Precambrian period • before Cambrian explosion • early origin of coelom hypothesized by trace fossils left in Precambrian sediments

Tissue • Epidermis covers body • made up of layers of cells • the middle embryonic layer is the mesoderm • here occurs the development of complex organs and organ systems to true muscle tissue • inner layer of cells forms intestine

Reproduction • Most Reproduce asexually • while some do reproduce sexually • the parent constricts in the middle • each half regenerates its missing end • cross-fertilization between individuals

Locomotion • Glide along a film of mucus, secreted by themselves • the cilia on the ventral epidermis able them to move

Digestion • Have a gastrovascular cavity with one opening • they lack a digestive tract • absorb nutrients across the body surface • branched gut to transport food

Cardiovascular • Lack organs for circulation • fluid filled spaces aid in transport

Respiratory • Lack organs for gas exchange • internal tissues are near the surface of the skin • this is because of their flattened bodies • gas and nutrients exchange with environment

Nervous • Pair of cerebral ganglia • longitudinal nerve cords connect to transverse nerves

Nematodaroundworms • Nematoda consist of no distinct classes • Nema - “thread” • 90,000 known species • do not have a respiratory system

Evolutionary Time Frame • Found as early as the Carboniferous period • fossils of nematodes were found in amber, these dated back to the Cenozoic era • relatives of nematoda date back to Cambrian • nematodes remain in the same form since then • because nematodes are microscopic, fossils are difficult to find • they lack hard body parts

Tissue Layers • Contain internal body cavity • pseudoderm • lack cilia and well-defined head • the epidermis (skin) is composed of a mass of cellular material and nuclei, these are not separated by membranes • a thick outer cuticle which is tough and flexible is secreted • this cuticle is shed, usually about four times before it becomes an adult • tough exoskeleton

Excretion • Some nematodes have specialized cells that excrete nitrogenous waste • canals are present in others to excrete wastes

Reproduction • Reproduce sexually with internal fertilization • males use copulatory spines to open female reproductive tract and inject sperm • sperm lack flagellae and move by pseudopodia • females are larger than males and deposit about 100,000 eggs a day

Locomotion • Muscles are longitudinal and contract producing a thrashing motion • only bend from side to side • muscle cells branch toward nerve • the internal pressure is high, this causes the body to flex, rather than flatten • nematoda have no cilia or flagellae

Digestion • Have mouth opening into pharynx (throat) • food is pulled in and crushed • pharynx leads to a long simple gut cavity lacking muscles • it is then led to the anus at the tip of the body • nutrients and wastes are distributed in body cavity • this is regulated by an excretory canal along each side of the body

Cardiovascular • No cardiovascular system • nutrients are transported through the body by fluid in the pseudocoelom

Nervous • Ring of nervous tissue around the pharynx • gives rise to two nerves: dorsal and ventral • nerve cords • run the length of the body • muscle cells branch toward nerve

Molluscasnails, slugs, oysters, clams, octopuses, squids • Over 150,000 known species • molluscous are soft bodied • protected by a hard shell made of calcium carbonate • Classes: • Plolyplacophora (chitons) • Gastropoda (snails and slugs) • Bivalvia (clams, oysters, bivalves) • Cephalopida (squids, octopuses, hautiluses)

Evolutionary Time Frame • Lived in freshwater streams as early as 400 million years ago • developed the ability to be able to live in most aquatic environments • 300 million years ago

Tissue • Three main parts: • Muscular foot (for movement) • visceral mass (containing the internal organs) • mantle (fold of tissue, drapes over visceral mass, secretes shell) • houses gills, anus, excretory pores • some produce a water filled chamber • called a mantle cavity

Excretion • Excretory organs called nephridia • remove metabolic wastes from hemolymph

Reproduction • Separate sexes with gonads in the visceral mass • life-cycle includes ciliated larva (trochophore)

Locomotion • Muscular foot • no bones • Outer shell made of calcium carbonate supports and protects • some also have inner shells for support • called cuttlebones in cuttlefish • pen in squids

Digestion • Feed by a strap like rasping organ called the radula to scrap food • ribbon like, hooked teeth • have jaw, pharynx, esophagus, stomach, intestine and anus

Cardiovascular • Open circulatory system • no true heart • blood is pumped along by vessels and join with open sinuses • bathes internal organs

Respiratory • Gills housed in mantle cavity • function in gas exchange • terrestrial snails lack gills • instead, lining of mantle cavity functions as a lung • exchanges respiratory gases with air

Nervous • Clams and chitons have no nervous system • squid and octopus have most sophisticated nervous system of all vertebrates • they have large brains and eyes • giant axon transmits messages

Annelidsearthworms, leeches, marine worms • 15,000 species • Three classes: • Oligochaeta (earthworms) • Polychaeta (polychaetes) • Hirudinea (leeches) • Annelids means “little rings” • segmented worms

Evolutionary Time Frame • Originated in Precambrian

Tissue • Coelom partitioned by septa • penetrated by digestive tract, longitudinal blood vessels and nerve cords

Excretion • Metanephridia • excretory tubes in each segment • ciliated funnels • remove waste from blood and coelomic fluid • lead to exterior pores, discharges waste • nephridia excrete waste • these are coiled tubes with expanded funnel shape (nephostrome, attached to septum) • leads to outside on posterior end

Reproduction • Cross-fertilization • Sperm is stored • clitellum secretes a mucous cocoon • cocoon picks up eggs and stored sperm • some reproduce asexually by fragmentation

Animal Evolution