P. Cnidaria

1
P. Cnidaria

• Characteristics
• 9000 sp.
• 4 classes
• Hydrozoa (hydroids, Portuguese MOW)
• Scyphozoa (true jellyfish)
• Cubozoa (cube jellyfish)
• Anthozoa (sea anemones, stony coral)
• early divergence among metazoans
• cnidocytes (stinging cells) w/ nematocysts
  (stinging organelles)
• great predators
• other sp. eat hydroids and acquire stinging
  defense
• shallow/deep water, mostly marine/few freshwater
• mostly sessile/poor swimmers
• symbiotic/commensal
• coral reef building w/ algae

2
P. Cnidaria

• radial/biradial symmetry
• oral/aboral ends w/ no head
• 2 body forms
• polyp/medusae
• exo-/endoskeleton
• chitin/CaCO3/protein
• diploblastic
• gastrovascular cavity w/ 1 opening surrounded by
  tentacles
• nematocysts in epidermis/gastrodermis/tentacles
• nerve net
• muscular system
• asexual/sexual reproduction (monoecious/dioecious)
  w/ planula larva
• no respiratory/excretory system
• no coelom

3
P. Cnidaria Body Form

• Many are dimorphic or polymorphic
• dimorphic forms sessile polyp/hydroid,
  free-floating medusa
• both still sac-like bodies
• Medusae body
• bell-shaped
• tetramerous symmetry
• concave
• tentacles extend from oral end

4
P. Cnidaria Body Form

• Polyp body
• tubular, mouth surrounded by tentacles (oral end)
• blind gut/gastrovascular cavity
• attached by pedal disc (aboral end)
• asexual reproduction
• budding knob on side forms mouth/tentacles
• falls off or stays attached
  (colony)
  sharing
  gastrovascular cavity
• allows differentiation of func.
• hydranth feeding polyp
• gonangia reproductive
  polyp, lack
  tentacles
• fission
• pedal laceration

5
P. Cnidaria Life Cycle

• Zygote develops into motile planula larva
• planula lands on surface, develops into polyp
• polyp asexually produces colony
• asexually produces medusae via strobilation or
  budding
• medusae reproduce sexually
• dioecious
• Reduced polyp in
  true
  jellyfish
• Others reduced
  medusae
• Port. MOW inflated polyp
• no medusae
• sea anemone, corals
• Hydra

6
P. Cnidaria Body Wall

• Epidermis derived from ectoderm
• gland/sensory/nerve cells, cnidocytes
• Gastrodermis derived from endoderm
• digestion
• Gelatinous mesoglea btwn
• imparts flexibility/elastic skeleton
• Bend/contract/pulse via myofibrils

7
P. Cnidaria Cnidocytes

• Tentacles w/ cnidocytes (stinging cells)
• located w/i invaginations of ecodermal/gastroderma
  l cells
• cnidae organelle of cnidocyte, discharged
• tiny thread bursts from nematocyst (2 m/sec)
• after discharge of cnida, cnidocyte is
  absorbed/replaced
• nematocyst type of cnida, injects toxin during
  prey capture/defense
• capsule w/ coiled thread covered by operculum
  (lid)
• barbs/spines
• cnidocil cilia trigger (mechanoreceptor)

8
P. Cnidaria Feeding and Digestion

• Feeding/digestion
• mostly carnivores
• capture w/ tentacles, insert into
  gastrovascular
  cavity
• extracellular digestion, ingest food broth
• algae provide additional C source
  for corals

9
P. Cnidaria Nerve Net

• Nerve net
• diffuse nervous system not CNS
• groups of nerves ring nerves and marginal sense
  organs
• 2 nerve nets
• nerve processes (axons) end at synapses or
  junctions w/ other cells
• impulses transmitted by release of
  neurotransmitter on 1 side of synapse or junction
• difference from more complex animals
• bidirectional release, lack of myelin
• neuromuscular system contractile fibers nerve
  net
• arose early in metazoan evolution

10
P. Cnidaria C. Hydrozoa

• C. Hydrozoa
• mostly marine, colonial
• life cycle
• asexual polyp gives rise to sexual medusa
• polyp and medusa are 2n
• gametes are 1n
• some lack polyp
  
  or medusa stage

11
P. Cnidaria C. Hydrozoa

• Hydra
• freshwater, solitary polyp on underside of lvs
• 25-30 mm
• cylindrical tube w/ basal disc at
  aboral end
• move by turning end over end
• epidermal cell types
• epitheliomuscular protection, contraction
• interstitial undifferentiated
• gland secrete adhesive cmpds/gas,
  at basal
  disc
• cnidocyte
• sensory cells 1 end has flagella for
  reception, other
  connects to other cells
• nerve cells

12
P. Cnidaria C. Hydrozoa

• gastrodermal cell types
• nutritive-muscular bring in food/water, some w/
  algae
• interstitial give rise to new cells
• gland digestive enzymes, mucous
• no cnidocytes
• feeding/digestion
• eat crustaceans/insect larvae/annelids
• hypostome w/ 6-10 tentacles that extend when
  hungry
• gastrovascular cavity
• prey harpooned by nematocysts
• mouth opens and prey inserted
• digestive enzymes secreted
  for
  extracellular digestion
• intracellular digestion
• waste expelled out mouth

13
P. Cnidaria C. Hydrozoa

• reproduction
• asexual via budding
• sexual
• temporary gonads in autumn
• cool temp., ? O2
• dioecious or monoecious
• zygotes develop into blastula
• cyst forms around embryo
• hatch in spring

14
P. Cnidaria C. Hydrozoa

• Obelia (hydroid colonies)
• polyp and medusa stages
• hydroid body base (hydrorhizza attachment)
  stalk (hydrocauli) individual polyps (zooids)
• most zooids are hydranths/gastrozooids
• feeding func.
• similar feeding as Hydra but
  common
  gastrovascular cavity
  w/ gastrodermal cells
• circulation via contraction and cilia

15
P. Cnidaria C. Hydrozoa

• medusa body
• bell-shaped, margins tuck under/inward (velum)
• mvmt via weak pulsing of filling/emptying cavity
• manubrium stalk w/ mouth, leads to stomach
• 4 radial canals connect w/
  ring
  canal around margin
• ring canal connects to
  
  tentacles
• nerve rings at base of velum
• have statocysts/ocelli

16
P. Cnidaria C. Hydrozoa

• asexual repro. via budding
• sexual repro. via gonangium (repro. polyp)
• produce free-swimming medusa which produce
  gametes
• gametes fuse and develop into free-swimming
  planula larva
• larva develops into polyp which produces more
  polyps

17
P. Cnidaria C. Hydrozoa

• Portuguese man-of-war (Physalia)
• colony
• tentacles zooids w/ nematocysts
• pneumatophore air sac
• Hydrocorals
• secrete calcareous skeletons
• similar to true corals

18
P. Cnidaria C. Scyphozoa

• Characteristics
• jellyfish
• mulitcolored
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