BIOL 201 Chp 7 Cnidaria


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This is a lecture presentation for my BIOL 201 Invertebrate Zoology students on Chapter 7: Cnidaria (Invertebrate Zoology, 7th Ed. by Ruppert, Fox, & Barnes, 2004).

Rob Swatski, Assistant Professor of Biology, Harrisburg Area Community College - York Campus, York, PA.

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BIOL 201 Chp 7 Cnidaria

  1. 1. Chapter 7: CnidariaBIOL 201: Rob Swatski Asst. Prof. BiologyInvertebrate Zoology HACC-York
  2. 2. PhylumCnidaria Hydra, anemones, stony & soft corals,hydroids, & jellyfishesMost marine (10,000sp); few FW (20 sp); no terrestrial sp Colonial or solitaryCorals build reefs (#2 biodiversity) 2
  3. 3. CnidariaStructure & Function Cnidocytes! Body plan resembles gastrula; mouth surrounded by tentacles Coelenteron (Gastrovascular cavity, GVC) Radial symmetry around oral-aboral axis: advantage? 3
  4. 4. Body Forms Polyp Medusa Sessile &Resembles Pedal disc Umbrella Manubrium: benthic; “Mouth- flower & & oral or bell- “elephant “mouth- down” stem disc shaped trunk” up” 4
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  8. 8. 3 Tissue LayersEpidermis: epithelium Gastrodermis: epitheliumMesoglea (gelatinous ECM): CT Diploblastic 8
  9. 9. ColonialCnidarians Reproduce via budding, but buds don’t separate Produce zooids that resemble juveniles Small zooids have large SA:V Fillter-feeding: many mouths & tentacles, broad distribution, small size 9
  10. 10. Types ofColonies Stolonate: have stolons (strawberry runners) Coenosarc: have coenosarc & solenia (hollow tubes) Fruticose: upright & branching; plantlike or featheryBudding: fixed-length(Obelia) & axial-polyp 10
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  12. 12. CnidarianSkeletons More diverse than sponges Exoskeletons: chitinous periderm (hydrozoans); calcium carbonate (stony corals); shellfragments (anemones)Endoskeletons: fibers& spicules (soft corals) or cell columns with turgid vacuoles (hydrozoans)Hydrostatic skeletons: Hydra, anemones 12
  13. 13. Musculature Antagonistic sheets of muscle Circular smooth muscle in gastrodermis Longitudinal smooth muscle in epidermis Coronal muscles around medusa subumbrella 13
  14. 14. Diversity ofMovement Polyps: shorten, extend, & bend Medusae: constrict bells for swimming Some polyps inch- worm & somersault! Tentacles move for prey manipulation Subumbrella retracts in polyps & medusae 14
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  16. 16. NervousSystems Two nerve nets:base of epidermis &gastrodermis; joined by nerve bridges across mesogleaNerve impulses cantravel any direction (radial sensory system) Medusae: nerverings, musculature, ganglia, & senseorgans around bell Statocysts, ocelli,chemoreceptors, &mechanoreceptors 16
  17. 17. Cnidocytes Used for prey capture & defense Cnidocytes (cells) contain cnida (fluid- filled capsule with tubule) Nematocytes contain nematocyst that stings & releases toxins Spirocytes contain spirocyst that contains sticky threads for adhesion 17
  18. 18. Cnidocytes, cont. Cnidocytes: abundant in epidermis, on tentacles, in gastrodermis Chemical & mechanical cues from prey trigger firing of nematocyst Toxins interfere with Na+/K+ pumps or degrade cell membranes Hydra discharges 25% of nematocysts eating 1 brine shrimp (replaced in 24hr) 18
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  20. 20. Nutrition & Internal Transport Coelenteron (GVC): blind gut Septa increase SA for digestion, absorption, gas exchange, excretion, repro, hydrostatic skeleton Radial & ring canals in medusae radiate out from central stomach Coelenteron often branches into each tentacle 20
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  22. 22. FeedingPrey is caught, mouthopens, tentacles stuff prey inside, & enzymes digest extracellularyGastrodermis absorbs nutrients & largerparticles are digested intracellularlySlow process, taking several days Wastes ejected out through mouth 22
  23. 23. Nutrition &Circulation Many species have PSN endosymbionts May account for 90% of nutrition in some species Often defined patterns of fluid circulation around coelenteron Ciliated gastrodermis; muscular contractions 23
  24. 24. Gas & WasteExchange Gas exchange occurs across general body surfaces: tentacles, body wall Waste exchange (excretion) occurs across body wall Ammonia is primary waste product Terrestrial inverts are adapted for conserving water during excretion 24
  25. 25. GeneralReproduction Amazing regenerators! Can lose oral end & regrow it Anemones can fully recover from dissections Clonal reproduction is common in polyps, but less common in medusae 25
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  27. 27. SexualReproduction Sexual repro in most: some monoecious (hermaphroditic); most dioecious Germ cells develop in gastrodermis & gametes released into coelenteron Most have external fertilization; some internal fertilization Zygote develops into planula larva, settles with aboral end down, & develops into juvenile polyp 27
  28. 28. ClassAnthozoa “Flower animals”Sea anemones, corals, sea fans, & sea pensLargest class: 6000 sp; solitary or colonialNo medusa phase in lifecycle 28
  29. 29. AnthozoanBody Form Long pharynx attached to coelenteron Many septa, 6-192 depending on species size Some have acontia: stringy filaments attached near septa base Heavily armed: spew from mouth as anemone deflates 29
  30. 30. Musculature Mostly epidermal & gastrodermal epitheliomuscular cells Epidermal musculature: controls tentacles & oral disc Gastrodermal musculature: controls body column 30
  31. 31. Retraction Controlled by retractors (longitudinal septal muscles) Tentacles & oral disc deflate & pulled into body Mesogleal sphincter muscle closes opening (draw-string) Must remove pump water out to retract; siphonoglyph cilia beat inwards to31 pump water back in
  32. 32. Diversity of Class Anthozoa Subclass Subclass Alcyonaria Zoantharia (Octocorallia) (Hexacorallia) Order Order Order Order Order Gorgonacea: Pennatulacea: Stolonifera:Actiniaria: Scleractinia: sea fans, sea pens, organ pipeanemones stony corals whips, & feathers, & corals plumes pansies 32
  33. 33. Subclass Zoantharia:Order Actiniaria Hexamarous symmetry: septa & tentacles in multiples of 6 Sea anemones: 1350 sp; brightly colored; most <10 cm Some have unique methods of locomotion Burrowing via peristalsis; walking on tentacles; swimming by thrashing tentacles 33
  34. 34. OrderActiniaria: TraitsCarnivorous suspension feeders: mucus traps particles on tentacles, moved to mouth Photosynthate: mayhave 2 sets of tentacles: false for PSN (exposed during day) & true (exposed during night)Clonal repro via pedal lacerationGonads located in septa 34
  35. 35. OrderActiniaria: Ecology Hermit crabs wear anemone on shell & will transfer to new shells Anemone gets substrate, food, protection, access to mates; Crab gets camouflage & protection Clownfish has protective surface mucus Anemone gets food, removal of sediment & necrotic tissue; Clownfish gets protection & food scraps 35
  36. 36. SubclassZoantharia: OrderScleractinia Stony corals (3600 sp); close relation to anemones Secrete CaCO3 exoskeleton that can weigh tons Produce cups (corallites) that they retract into Most colonial polyps, 1-3mm diameter 36
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  39. 39. SubclassZoantharia: OrderScleractinia Corals are often very colorful due to PSN endosymbionts Algae often released in conjunction with gametes Coral bleaching can occur under stressful environmental conditions Incorrect light/UV intensity, salinity, temp (even 1°C) 39
  40. 40. SubclassAlcyonaria: OrderStolonifera Octomerous symmetry: septa/tentacles in multiples of 8 Soft corals: don’t produce CaCO3; organ pipe corals Most lack nematocysts; secrete noxious chemicals to deter predators More tolerant of environmental fluctuations 40
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  42. 42. SubclassAlcyonaria: OrderGorgonacea Plant-like sea whips, fans, & plumes Highly branched Endoskeleton: axial rod made of gorgonin (highly cross-linked collagen) 42
  43. 43. Subclass Alcyonaria: OrderPennatulacea Sea pens, feathers, & pansies 43
  44. 44. Medusozoa Medusa phase in life cycle: planula  polyp  medusa Tetramerous radial symmetry: multiples of 4 Cnidae are all nematocysts 2 major classes: Scyphozoa (large jellies) & Hydrozoa (small jellies - Hydra, & hydroids) 44
  45. 45. ClassScyphozoa 200 sp of large jellies Polyps: small & funnel-shaped (scyphistomae) Coelenteron divided by 4 septa Have 4 septal funnels that circulate water to gonads in adults 45
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  47. 47. ClassScyphozoa:Body Form Medusa bells: 2-40 cm diameter Manubrium divided into 4 oral arms Tentacles located around periphery of bell 47
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  49. 49. ClassScyphozoa:Body Form Coelenteron divided by septa into 4 gastric pockets 4 pairs of gonads in septa & 4 septal funnels Many have radial canals & marginal canals Gastrodermal cilia circulate water 49
  50. 50. ClassScyphozoa:Body Form, cont. Lappets: rounded lobes on umbrella margin Rhopalia: sensory organs in grooves b/w lappets Statocysts: mechanoreceptors (also chemoreceptors & photoreceptors) Nerve net & nerve ring 50
  51. 51. ScyphozoanReproduction Clonal: differentiate into strobila Stacked mini medusae separate via transverse fission (strobilation) Juvenile medusae are called ephyra Adult medusae reproduce sexually 51
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  53. 53. Scyphozoan Diversity: 5 OrdersSemaeostomeae Rhizostomeae Coronatae Cubomedusae Stauromedusae Aurelia Stomolophus Linuche Chironex Haliclystus 53
  54. 54. ClassHydrozoaHydra & hydroids, firecorals, & Portugueseman-of-war; 3000 sp Most are colonies of polyp & medusa zooidsMedusa often form as buds, but are notreleased from colony Hydra life cycle does not include medusa phase 54
  55. 55. HydrozoanBody Plans Two types of polyps: Athecate (A-form) & Thecate (L-form) Zooids 1mm or smaller in length Large SA:Vol No gastrodermal septa 55
  56. 56. HydrozoanBody Plans Medusae arise from colony as lateral buds (not via strobilation) Velum: iris diaphragm on subumbrellar margin for swimming Hydroid colonies are sessile & benthic (seaweed- like) 3 colony forms: stolonate, coenosarcal, or fruticose 56
  57. 57. Hydrozoan A-form Colonies Athecate: lack theca (protective cup) Periderm ends at attachment point of zooids Typically grow via axial- polyp budding 57
  58. 58. Hydrozoan L-form Colonies Periderm forms a wine-glass shape theca Hydranth can retract into theca Theca may have a hinged lid (operculum) Grow via fixed-length budding 58
  59. 59. ZooidTerminology Monomorphic colonies: 1 type of zooid Gastrozooids: feeding hydranths Polymorphic colonies: several types of zooids Gonozooids: reproductive polyps Dactylozooids: have nematocysts for protection & food capture 59
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  61. 61. Class Hydrozoa: Order Anthoathecatae Hydra: both clonal & sexual repro, but no medusa stage Fire corals: reef builders with nasty sting Velella: by-the-wind sailor with a float & sail; extreme polymorphism, with zooids suspended61 mouth-down Hydra
  62. 62. Fire coral 62
  63. 63. 63 Vellela: By-the-wind sailor
  64. 64. Class Hydrozoa: Order Siphonophora Physalia: Portuguese man-of-war Pedal end of polyp bears a gas-filled float (pneumatophore) Buds arise from a column of polyp sets called cormidia (oldest near float) Possess diversity of zooids 64
  65. 65. Physalia 65
  66. 66. Class Hydrozoa: OrderLeptothecatae L-form hydroids: Obelia Feather-shaped colonies 66
  67. 67. Class Hydrozoa: OrderLimnomedusae L-form hydroids with both polyp & medusa phase Gonionemus 67
  68. 68. Credits by Rob Swatski, 2010 Visit my website for more Biology study resources! send your comments and feedback to: This work bears an Attribution-Noncommercial Share Alike Creative Commons license. 68