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Today’s Objectives: 3.4. Describe characteristics of this phylum Identify life functions of cnidarians Classify and give examples of phylum Cnidaria. Phylum Cnidaria. Animals with stinging cells. Characteristics of Cnidarians. Radial or biradial symmetry Tissue-level organization

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Today’s Objectives: 3.4

  • Describe characteristics of this phylum

  • Identify life functions of cnidarians

  • Classify and give examples of phylum Cnidaria

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Phylum Cnidaria

Animals with stinging cells

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Characteristics of Cnidarians

  • Radial or biradial symmetry

  • Tissue-level organization

  • Mesoglea between epidermis and gastrodermis

  • Gastrovascular cavity

  • Nerve net

  • Cnidocytes – used for defense or feeding

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Life Functions of Cnidarians

  • Reproduction/life cycle

    • Can be monoecious or dioecious

    • Alternate generations between medusa and polyp form

  • Feeding

    • Use cnidocytes to stun or kill prey

    • Can contract tentacles to bring to mouth

    • Digestion occurs in gastrovascular cavity

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Life Functions of Cnidarians

  • Support & locomotion

    • Hydrostatic skeleton

    • Some classes have longitudinal muscles for movement

    • Medusa move by contracting bell or jet propulsion

    • Some polyps can walk on tentacles, contract, inchworm or glide on pedal disks

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Reproduction in Cnidarians

  • Most are dioecious

  • Polyp can develop through budding or from a free-swimming planula larva

  • Medusa almost always formed by budding from a polyp body wall

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Classification of Phylum Cnidaria

  • Class Hydrozoa

  • Class Scyphozoa

  • Class Cubozoa

  • Class Anthozoa

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Class Hydrozoa

  • Mostly marine

  • This is the only class with freshwater members!

  • Alternate generations

  • Mostly colonial polyps

  • Only have cnidocytes in epidermis

  • Sperm & egg are released outside body

  • No amoeboid cells in mesoglea

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  • Gastrozooid – feeding polyp formed from planula larvae

  • Grows through budding into more gastrozooids

  • Gonozooid – reproductive polyp that forms medusa by budding

  • Medusae then reproduce sexually

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  • Medusa predominant - Dioecious

  • Has a velum (not found in other classes) which creates jet propulsion

  • Mouth at end of a manubrium

  • Nerve ring in addition to nerve net that coordinates swimming movements

  • Statocyst sensory structure that responds to gravity

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  • Freshwater

  • Polyp only, no medusa

  • Testes form sperm through meiosis

  • Ovaries form one egg each

  • Young “buds” from parent until ready to survive on its own, then it drops off

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  • Portuguese man-of-war

  • Colonial siphonophore

  • Does not swim, float moved by water and wind

  • Long dactylozooids (tentacles) contain cnidocytes and kill prey.

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Class Scyphozoa

  • “True Jellyfish” – polyp form reduced or absent

  • All marine

  • No velum

  • Mesoglea contain amoeboid cells

  • Cnidocytes in gastrodermis and epidermis

  • Gametes form in gastrodermis

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  • Extensively branched canal system

  • Gastrodermal cells have cilia to circulate food

  • Feeds on plankton

  • Rhopalium – chemosensors

  • Statocyst – gravity sensors

  • Lappets – touch receptors

  • Ocelli – photoreceptors

  • Planula develop into a scyphistomapolyp

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Class Cubozoa

  • Medusa is cuboidal

  • Tentacles hang from corners

  • Polyps reduced or absent

  • Ex. Sea wasp

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Class Anthozoa

  • No medusae, polyp only

  • Mouth has a pharynx

  • Gastrovascular cavity is divided into sections

  • Mesoglea contains amoeboid cells

  • Sexual and asexual reproduction

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Body structure of Anthozoans

  • Pedal disk

  • Oral disk

  • Siphonoglyph – moves water into gastrovascular cavity to maintain hydrostatic pressure.

  • Acontia– prevents live prey from damaging gastrovascular cavity.