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    Chapter 9Multicellular and Tissue Levels of

    Organization

    Phyla Cnidaria and Ctenophora

    ZoologyRick Knowles

    Liberty Senior High School

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    Who are the Cnidarians?

    Hydra

    Corals

    Sea Anemones

    Jellyfish

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    Whats a Ctenophora?

    Comb Jellies

    http://rds.yahoo.com/_ylt=A0S020w4.0lMaw8AuxGjzbkF/SIG=12rvs9lfd/EXP=1280003256/**http:/www.hoxfulmonsters.com/wp-content/uploads/2009/01/comb-jelly.jpghttp://rds.yahoo.com/_ylt=A0S020rD.klMUVIAIsCjzbkF/SIG=11uvv8se5/EXP=1280003139/**http:/conservativekids.net/comb_jelly.jpg
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    Phylum Cnidaria Characteristics

    Radial Symmetry (or biradialsymmetry)

    Diploblastic tissue-level organization

    Gel-like mesoglea between epidermaland gastrodermal tissue layers Gastrovascular Cavity

    Nerve net for a nervous system Have cnidocytes specialized cells

    used in defense and feeding

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    Radial Symmetry

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    Diploblastic Tissue Level

    Ectoderm becomes the epidermis, outerlayer of body wall.

    Endoderm becomes gastrodermis, inner

    layer of body wall. Epidermis and Gastrodermis can become

    many other cell types.

    Mesoglea is a jellylike layer betweenepidermis and gastrodermis; cells in themesoglea are from epi- or gastrodermis; not

    triploblastic.

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    Jellyfish Antomy Mesoglea - layer of

    jelly separating twotissue layers of cup orumbrella-shaped bodyforms.

    GastrovascularCavity a centralcavity that serves for

    digestion, circulationand reproduction witha single opening thatfunctions as both

    mouth and anus.

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    Some cnidarians, such as jellies: Have elaborate gastrovascular cavities

    Circular

    canal

    Radial canal

    5 cm

    Mouth

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    No Bones, No Brain, but What aSting!

    Cnidocytes specialized cells of cnidariansthat produce and contain stingingnematocysts; unique to Cnidarians.

    Cnida (ae) a fluid-filled capsule encasing acoiled hollow tube; used for attachment,defense, and feeding.

    Nematocyst a type of barbed cnida thatpenetrates prey; often delivers toxins.

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    Cnidarian Tentacles Tentacles may have several

    kinds of cnidae. Some cnidae produce mucus

    to entrap prey or anchor theanimal.

    Cnidocytes on the tentacleshave trigger structures that,when touched, release the

    coiled nematocyst; oftenbarbed, like a harpoon.

    Contains neurotoxins toparalyze prey.

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    Nemotocysts

    Discharged

    NemotocystFiring NemotocystNematocyst

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    Dead NH Jellyfish Stings 150 ,

    Hospitalizes 9

    Dead Lions ManeGiant Jelly, WallisSands State Park,NH, July 22,2010

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    Alternation of GenerationsMost Cnidarians have 2 Body Forms in Life

    Histories:1. Polyp the sessile (attached) state in the

    life cycle; cylindrical body and a mouth

    surrounded by tentacles; mouth upwards;usually asexual.

    2. Medusa the free-swimming stage in thelife cycle; shaped like inverted bowl; mouth

    usually points downward with tentaclesdangling at margin; usually is dioecious(either male or female) and produces

    gametes.; sexual.

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    Alternation of GenerationsPolyp Form

    attached tosubstrate at theaboral end withmouth facing

    upward.Medusa Form

    free swimmingwith mouthusually facingdownwardsurrounded by

    feeding tentacles.

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    Typical Jellyfish Life Cycle

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    Feeding and Digestion Carnivorous eat plankton, small

    crustaceans, fish, EACH OTHER!

    Tentacles snag prey and drag to mouth. Gastrodermis lines gastrovascular cavity

    (GVC) functions in digestion, exchange ofgases, respiration, and reproduction.

    Lions mane eats another jelly

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    Lions mane jellyfish eating fish

    Once in GVC,gastrodermal cells

    secrete digestiveenzymes andphagocytize food.

    Nutritive-muscularcells contract and helpdistribute food viaperistalsis.Undigested foodleaves via the mouth,no anus.

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    RespirationVia diffusion Body is only two cell

    layers thick.

    Jellies can be long andheavy but must bewithin 0.5 mm fromsurrounding water for

    diffusion large S.A. toVolume ratio.

    Use the GVC to helpwith this.

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    Internal Transport

    Via diffusion

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    Excretion

    Via diffusion

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    Movement Buoyancy from water; also hydrostatic

    skeleton from the GVC.

    Move on water current or wind.

    Epithelial cells in body wall can contractand push water from the GVC and outmouth polyp collapses.

    Circular and radial cells may causerhythmic pulsations of bell.

    May also walk along bottom withtentacles.

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    Responsiveness

    Most primitive nervous system in animals. Have a nerve net below epidermis carriesimpulses from local stimuli around the body.

    Some touch and chemical receptorsthroughout the body. Some species have a nerve ring at the

    margin of the medusa for swimming. Others have statocyst at the margin CaCo3sensitivity to gravity and coordinatesswimming.

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    Sexual Reproduction

    Dioecious either male or female; nothermaphrodite. Sperm or egg released into GVC or

    released into water for externalfertilization.

    Embryo develops into planula ciliated,free-swimming larva.

    Planula attaches to substrate, becomespolyp.

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    Asexual Reproduction

    Polyps mayform frombudding fromother polyps.

    Some usefission.

    Fission in Sea Anemones

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    Class Hydrozoa Small, common, marine and freshwater.

    Characteristics:1. Nematocysts only in epidermis

    2. Gametes are epidermal released into water andnot GVC.

    3. Incomplete digestive tract with unbranched gut.4. Mesoglea is acellular; mostly thin, gel-like.

    5. Polyp is dominant body from.

    Most have colonial polyps that are specializedfor feeding, budding, defense. Ex. Hydra, Obelia, Gonionemus, Physalia

    physalis(Portugese man-of-war)