Transcript phylum-cnidaria

Phylum
Cnidaria
Phylum Cnidaria
• jellyfish, hydras, sea
anemones, corals
• carnivorous
• radial symmetry
• have stinging cells called
cnidocytes which contain
nematocysts
• nematocysts are poison
filled harpoons used for
catching prey
Body Symmetry
Radial Symmetry
Bilateral Symmetry
Posterior end
Dorsal side
Anterior end
Ventral
side
Plane of
symmetry
Planes of
symmetry
Cnidarian Body Plan
• radial symmetry with tentacles
• two stages to life cycle
– Polyp
– Medusa
• body surrounds an internal space,
gastrovascular cavity
• gastrovascular cavity lined with gastroderm
(tissue layer)
• epidermis is outermost layer
• mesoglea between gastroderm and epidermis
(jelly-like)
Polyp
• Sessile
• cylindrical body
• mouth faces upwards
• tentacles point up
Medusa
• Motile
• bell-shaped body
• mouth underneath
• tentacles point down
The Polyp and
Medusa Stages
Epidermis
Mesoglea
Gastroderm
Tentacles
Mesoglea
Gastrovascular cavity
Mouth/anus
Mouth/anus
Gastrovascular
cavity
Tentacles
Medusa
Polyp
Feeding
• prey is paralyzed and pulled into the
gastrovascular cavity
• digestion is extracellular
• nutrients are absorbed by gastroderm
• nutrients dispersed by diffusion
• anything not digested leaves through the
mouth/anus
Respiration, Circulation, Excretion
• all are done by diffusion through the body wall
Response
• specialized cells of the nerve net receive
stimuli
• nerve net is evenly distributed throughout
the body
• no true brain
• also have cells to determine light intensity
and gravity
Movement
• done by hydrostatic skeleton in polyps
• done by jet propulsion in medusa (like a
water pump)
Reproduction: Sexual
•
•
•
•
•
fertilization is external
separate male and female organisms
zygote forms a free-swimming larva
larva grows into a new polyp
polyp then buds to form new medusa
Reproduction: Asexual
• polyps reproduce by budding
• new polyps may grow off the side of
existing polyps
• polyp may produce medusas
Jellyfish Life Cycle
Female medusa
(2N)
Adult
medusas
reproduce
sexually by
releasing
gametes into
the water.
MEIOSIS
Fertilization occurs in the open
water, producing many diploid
zygotes.
Egg (N)
FERTILIZATION
Sperm (N)
Zygote (2N)
Male medusa
(2N)
Young
medusa
The polyp
buds to
release
young
medusas.
Haploid
Diploid
Each zygote grows
into a ciliated larva.
The larva eventually
attaches to a hard
surface and develops
into a polyp.
Swimming larva
Budding
polyp
Polyp
Jellyfish
• class Scyphozoa (cup
animal)
• life is spent mostly in
medusa stage
• larva and polyp stage
are usually the same
• reproduce sexually
Hydras
• class Hydrozoa
• usually grow in
colonies
• no medusa stage in
life cycle of
freshwater hydras
• may reproduce either
sexually or asexually
Anemones and Corals
• class Anthozoa
(flower animals)
• only have a polyp
stage in their life cycle
• many are colonial
• reproduce sexually
(some asexually)
• larva forms a new
polyp