Transcript Cnidarian and Ctenophore ppt

2. Cnidarians
2. Cnidarians
• Next evolutionary jump
– Cells form tissues that perform specific functions
• Sometimes called coelenterates
– Include sea anemones, jellyfish, and corals
Cnidarians: Structure
• Finally, we see a pie that can be sliced!
• Cnidarians actually exhibit radial symmetry
in which similar body parts can be grouped around a central axis.
• If cut like a pizza, all slices would be similar
• Look the same from all sides
• No head, front, or back
Cnidarians: Structure and Function
• Oral surface and aboral surface
• Central mouth with tentacles
• Mouth open into a gut (only one opening)
• Capture prey with nematocysts (stinging structures found
within tentacles)
– When cells are touched, water pressure causes nematocysts to protrude
• Cnidocytes – cells which contain nematocysts
Discharged nematocysts,
stingingcells used for defense
and prey capture, have been
the plague of more than fish.
Stings from certain jellyfish
have resulted in death in a
matter of hours, especially
for infants.
Carukia barnesi: the badest of the bad!
Irukandji syndrome:
A sting from this little guy can cause the following:
“It begins with a mild sting, followed by severe lower back pain,
muscle cramps in arms, legs, stomach and chest. It causes sweating,
anxiety, nausea, vomiting, headaches and palpitations, and has also
been known to cause cardiac failure.”
Cnidarian: Structure and Function
Feeding and Digestion
•Carnivores
•Use nematocysts to capture prey
– Each contain fluid filled capsule
containing thread that is ejected
– May be spines or long tube that
wraps around prey
– Toxic
Cnidarian: Structure and Function
Feeding and Digestion
•Extracellular digestion – outside of the cells
•Intracellullar digestion – within cells in the lining of the gut
Cnidarian: Structure and Function
Behavior
•Lack brain and true nerves
•Nerve cells interconnect forming nerve net that transmits
impulses in all directions
•Sea anemones can tell if other member is from same clone
– Known to attack and even kill anemones from other clones
Cnidarian: Structure and Function
Behavior
•Some medusae have primitive eyes
•Medusae have statocysts, small calcareous bodies in fluid-filled
chambers surrounded by sensitive hairs, to help with balance
Cnidarians: Structure and Function
1. Polyp: a sac-like attached
stage with a mouth and
tentacles (mostly sessile)
2. Medusa: a mobile bell-like
upside down polyp
(jellyfish).
Cnidarians: Structure and Function
• Larva is called planula, ciliated stage with two cell layers
– Settles and metamorphoses into a polyp or develops into medusa
Cnidarians: Structure and Function
• Two layer of cells form body wall; one is epidermis (“skin”)
and other is gastrodermis (gut lining)
• Gelatinous middle layer is mesoglea, does not contain cells
– In medusa this layer expands to form gelatinous domed
bell
Types of Cnidaria
Cnidaria come in all shapes and sizes.
•Hydrozoans- feathery hydroids
•Scyphozoans- large jellyfish
•Anthozoan-sea anemones and coral
Sea fan
•Most of the animals found within Cnidaria are all carnivores.
Cnidarian Types
Hydrozoans (class Hydrozoa)
•Feathery or bushy colonies of tiny polyps attached to pilings,
shells, seaweeds, and other surfaces
•Polyps may be specialized for feeding, defense, or reproduction
•Reproductive polyps produce minute, planktonic medusae
Cnidarian Types
Hydrozoans (class Hydrozoa)
•Medusae release gametes & fertilized eggs develop into free
swimming planula larvae
•Each planula larvae settles and develops into a polyp
•The poylp divides repeatedly and develops into a colony
•Some lack poylp stage and develop into a medusae
•Few lack medusae stage and develop into gamete producing
polyps
Cnidarian Types
Scyphozoans (class Scyphozoa)
•Larger jellyfish
•Large medusae are dominate stage in life cycle
•Polyps small & release juvenile medusae
•Few lack polyp stage
•Bell diameter ranges from 2-3 meters, depending on water depth
Cnidarian Types
Scyphozoans (class Scyphozoa)
•Swim with rhythmic contractions of bell but easily carried by
currents
•Some species stings range from rash to fatalities
•Cubomedusae once classified as Scyphozoa now in own class
Cubozoa (box jelly)
Cnidarian Types
Anthozoans (class Anthozoa)
•Anemones and corals
•Solitary or colonial polyps that lack medusae stage
•Largest number of species
•Polyps are more complex
– Gut contain septa increasing surface area for digestion of
large prey
– Septa provide support for larger species
•Sea anemones have large polyps
Cnidarian Types
Anthozoans (class Anthozoa)
•Corals – colonial anthozoans
•Carbonate skeletons
•Occur in cold waters; tropical waters form reefs
•Gorgonians (sea fans) secrete branching skeleton made of
protein
– Precious corals gorgonians are fused with red or pink
calcareous spicules in addition to protein skeletons
Cnidarian Types
Anthozoans (class Anthozoa)
•Black Corals secrete hard, black protein skeleton
•Used for jewelry
3. Comb jellies: Ctenophora
Similar to cnidarians in most
respects.
Nearly 100 spp.- all marine
Contain ciliary combs which
assist in prey capture and mobility.
3. Comb jellies: Ctenophora
Gelatinous body with 8 rows of combs that beat in
waves
Beating of combs refracts light creating multicolor
effect
Body length range from few millimeters to 2 m
http://www.youtube.com/watch?v=
G7WT81ukHZE
3. Comb jellies: Ctenophora
Found in warm and cold waters
Carnivores
Swarms consume large numbers of fish larvae and other plankton
Capture prey with long tentacles with colloblasts (sticky cells)
Few have nematocysts