1. 2. Cnidarians

2. 2. Cnidarians Next evolutionary jump Sometimes called coelenterates
Cells form tissues that perform specific functions
Sometimes called coelenterates
Include sea anemones, jellyfish, and corals

3. 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

5. 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

6. 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.

7. 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.”

8. 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

9. Cnidarian: Structure and Function
Feeding and Digestion
Extracellular digestion – outside of the cells
Intracellullar digestion – within cells in the lining of the gut

10. 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

11. 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

12. 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).

13. Cnidarians: Structure and Function
Larva is called planula, ciliated stage with two cell layers
Settles and metamorphoses into a polyp or develops into medusa

15. 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

17. Types of Cnidaria Cnidaria come in all shapes and sizes.
Sea fan
Cnidaria come in all shapes and sizes.
Hydrozoans- feathery hydroids
Scyphozoans- large jellyfish
Anthozoan-sea anemones and coral
Most of the animals found within Cnidaria are all carnivores.

18. 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

19. 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

21. 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

22. 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)

23. 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

25. 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

27. Cnidarian Types Anthozoans (class Anthozoa)
Black Corals secrete hard, black protein skeleton
Used for jewelry

28. 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.

29. 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

30. 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