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Phylum
Cnidaria
Jellyfish, Coral, Sea Anemone, and
Hydroids
Cnidarians
• Stinging cell animals
• Also Known As: Coelenterates: “Hollow
Gut”
• Radial Symmetry: similar body parts
surrounding a central axis
Body Plan
• No segments: oral and aboral sides
• Hydrostatic Skeleton: fill body cavity with water
to remain upright.
• Shrink down as defense
• Organized at tissue level. (No true organs)
• Epidermis: outer cells (ectoderm)
• Gastrodermis: lines stomach (endoderm)
• Mesoglea: middle layer of gelatinous material; can
be thick or thin.
Digestion
• Food is digested in the sac-like digestive
cavity (only one opening)
• Extracellular and intracellular digestion
• Extracellular: outside of cells
• Intracellular: inside of cells
• Waste is expelled out of the mouth
Unique Features
• Cnidoblasts: stinging cells
• Inside each cell is a nematocyst, coiled thread with
barb at the end.
• The nematocyst can be discharged by either
physical or chemical stimulus.
• Physical- cnidocil (modified flagella) acts as a
trigger
• Contain a poisonous neurotoxin, varies by species
Cnidoblast
Nematocyst
Nervous System
• Nerve cells interconnect to form a nerve net
Life Cycle
• Jellyfish have separate sexes
• Both sexual and asexual reproduction
• Sexual: external or internal (depending on
species), sperm and egg form a zygote
which grows into a swimming larva called
the planula.
• In some cases the planula attaches to a hard
substrate and develops into a polyp.
Life Cycle cont.
• The polyp resembles an upside-down
jellyfish medusa.
• Small umbrella like medusas break off from
the polyp by budding (asexual)
Classification of Cnidarians
• Class Hydrozoa- Hydra, Physalia, and
Obelia
• Class Scyphozoa- True Jellyfish
• Class Cubozoa- box jellyfish
• Class Anthozoa- Corals and Sea Anemones
Class Hydrozoa
• Usually colonial, except Hydra
• Composition of colonies- 3 types
1. Gastrozoid- responsible for feeding
2. Gonozoids- responsible for sexual
reproduction
3. Dactyliozoids- responsible for defense;
have numerous nematocysts.
Class Scyphozoa
• All marine; medusa is dominant life cycle
• Mesoglea is a large part of the body (mostly
dead matter)
• Gastroderm have nematocysts; food may be
eaten alive
• More toxic than hydrozoans
• Well developed sensory organs and glands
- eyespot and chemoreceptors
Class Cubozoa
• Cube-like jellyfish
• Have four flattened, blade-like structures
called pedalia
• Complex eyes with lenses and retinas (no
brain though)
• Only 16 species: Irukandji and Chironexdeadly box jellyfish. Can kill a human in
minutes.
Irukandji: Carukia barnes
• One of, if not the
deadliest box
jellfish.
• 2.5 cm (1 inch) in
diameter
Box Jellyfish Sting
Chironex- Sea Wasp
Class Anthozoa
• No medusa stage in life cycle
• Polyps produce eggs and sperm that
develop into planula larva
• Solitary: sea anemone
• Colonial: coral
Tube Sea Anemone
Sea Anemone
Soft Coral
Corals and Coral Reefs
• Corals are colonial cnidarians
• Dominant form is the polyp
• Coral reef is a massive structure composed
of calcium carbonate built by coral polyps
and the organisms that live with in them
• The polyps take up calcium in the sea water
and zooxanthellae, which live inside the
polyp, take up CO2, which make limestone
Zooxanthellae
Hard Coral
Coral Reefs
• Found only in tropical areas
• Warm and clear water
• Shallow water- zooxanthellae require
sunlight to photosynthesize
• Zooxanthellae are the primary producers of
the coral reef
Coral Reef Formation
• Fringing Reef: occurs when a seamount pierces
the sea surface to form an island and provides a
base on which the coral can grow
• Barrier Reef: occurs if a seamount subsides
slowly enough and the coral continues to grow
upward at a rate that is not exceeded by the rising
water. A lagoon is formed.
• Atoll- occurs if the seamount disappears below the
surface and the coral reef is left as a ring.
Atafu Atoll: South Pacific
Symbiosis and Cnidarians
• Symbiosis: literally means to live together
1. Mutualism: both organisms benefit from
living together
2. Commensalism: one organism benefits,
the other is unaffected
3. Parasitism: one organism benefits, one is
harmed.
Clownfish and Anemones
Sea Anemones and Clownfish
• Usually, fish the size of clownfish are stung and
eaten by an anemone
• Clownfish become immune to the anemones
nematocysts because of a mucus coating
• The mucus inhibits the anemone’s sting
• The anemone provides protection and scraps of
food for the clownfish
• The clownfish lures prey into the anemone and
cleans the anemone
• What kind of relationship is this?______________
Coral and Zooxanthellae
Corals and Zooxanthellae
• Zooxanthellae are dinoflagellates that are taken up
by the coral polyps.
• Zooxanthellae contain chloroplasts
• Coral use the glucose made by the zooxanthellae
as an energy supplement
• The zooxanthellae benefit because they are
protected and receive nutrients from the coral
polyp.
• What type of relationship is this? _____________
Phylum Ctenophora
Comb Jellies
Take notes on your own sheet of
paper, only write down what is
underlined.
Ctenophora
Ctenophora
•
•
•
•
Group of 100 species
Oval shaped with radial symmetry
Resemble cnidarians but are NOT!
Swim with 8 rows of ciliary combs (long
cilia fused at the base)
• Cilia refract light which
cause a rainbow effect.
• Body length varies from a few centimeters
to 2 m long.
Habitat
• Exclusively marine
• Can be found in cold or warm water
Diet
• Carnivores
• Consume fish larvae and plankton
• Can expand stomach to eat organisms twice
their size.
• Capture prey with two long tentacles armed
with sticky cells called colloblasts
• A few species have nematocysts
Reproduction
• Sexual reproduction
• Hermaphrodites
• No polyp form; only medusa
Life Cycle
Deep Sea Comb Jelly
On a sheet of paper do the following
1) Title the paper: Porifera, Cnidaria, and
Ctenophora Lab
2) Number your paper from 1-22
3) Leave space on #11, #14 and #16 for
drawings (about 5 lines)
4) Use your Porifera Notes and Cnidaria
Notes to answer the questions (answers
only, don’t worry about writing the
questions)