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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

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2 cnidarians1
2. Cnidarians

  • Next evolutionary jump

    • Cells form tissues that perform specific functions

  • Sometimes called coelenterates

    • Include sea anemones, jellyfish, and corals

Cnidarians structure
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
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

2 cnidarians

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.

2 cnidarians

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
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 function1
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 function2
Cnidarian: Structure and Function


  • 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 function3
Cnidarian: Structure and Function


  • 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 function1
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 function2
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 function3
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
Types of Cnidaria

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.

Cnidarian types
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 types1
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 types2
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 types3
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 types4
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 types5
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 types6
Cnidarian Types

Anthozoans (class Anthozoa)

  • Black Corals secrete hard, black protein skeleton

  • Used for jewelry

3 comb jellies ctenophora
3. Comb jellies: Ctenophora

Similar to cnidarians in most


Nearly 100 spp.- all marine

Contain ciliary combs which

assist in prey capture and mobility.

3 comb jellies ctenophora1
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


3 comb jellies ctenophora2
3. Comb jellies: Ctenophora

Found in warm and cold waters


Swarms consume large numbers of fish larvae and other plankton

Capture prey with long tentacles with colloblasts (sticky cells)

Few have nematocysts