2. Cnidarians

2. Cnidarians2. Cnidarians

2. Cnidarians2. Cnidarians

• Next evolutionary jumpNext evolutionary jump– Cells form tissues that perform specific functionsCells form tissues that perform specific functions

• Sometimes called coelenteratesSometimes called coelenterates– Include sea anemones, jellyfish, and coralsInclude sea anemones, jellyfish, and corals

Cnidarians: StructureCnidarians: Structure

• Finally, we see a pie that can be sliced!Finally, we see a pie that can be sliced!

• Cnidarians actually exhibit Cnidarians actually exhibit radial symmetryradial symmetry in which similar body parts can be grouped around a central axis.in which similar body parts can be grouped around a central axis.

• If cut like a pizza, all slices would be similarIf cut like a pizza, all slices would be similar

• Look the same from all sidesLook the same from all sides

• No head, front, or backNo head, front, or back

Cnidarians: Structure and FunctionCnidarians: Structure and Function

• Oral surface and aboral surfaceOral surface and aboral surface

• Central mouth with tentaclesCentral mouth with tentacles

• Mouth open into a gut (only one opening)Mouth open into a gut (only one opening)

• Capture prey with Capture prey with nematocystsnematocysts (stinging structures found (stinging structures found within tentacles)within tentacles)– When cells are touched, water pressure causes nematocysts to When cells are touched, water pressure causes nematocysts to

protrudeprotrude

• Cnidocytes Cnidocytes – cells which contain nematocysts– cells which contain nematocysts

Discharged Discharged nematocystsnematocysts, , stingingcells used for defense stingingcells used for defense and prey captureand prey capture, , have been have been the plague of more than fish. the plague of more than fish. Stings from certain jellyfish Stings from certain jellyfish have resulted in death in a have resulted in death in a matter of hours, especially matter of hours, especially for infants.for infants.

Irukandji syndrome:Irukandji syndrome:

A sting from this little guy can cause the following:A sting from this little guy can cause the following:

““It begins with a mild sting, followed by severe lower back pain, It begins with a mild sting, followed by severe lower back pain, muscle cramps in arms, legs, stomach and chest. It causes sweating,muscle cramps in arms, legs, stomach and chest. It causes sweating,anxiety, nausea, vomiting, headaches and palpitations, and has alsoanxiety, nausea, vomiting, headaches and palpitations, and has alsobeen known to cause cardiac failure.been known to cause cardiac failure.””

Carukia barnesi: the badest of the bad!Carukia barnesi: the badest of the bad!

Cnidarian: Structure and FunctionCnidarian: Structure and Function

Feeding and DigestionFeeding and Digestion•CarnivoresCarnivores•Use nematocysts to capture preyUse nematocysts to capture prey

– Each contain fluid filled capsule Each contain fluid filled capsule containing thread that is ejectedcontaining thread that is ejected

– May be spines or long tube that May be spines or long tube that wraps around preywraps around prey

– ToxicToxic


Feeding and DigestionFeeding and Digestion

•ExtracellularExtracellular digestion – outside of the cells digestion – outside of the cells

•Intracellullar Intracellullar digestion – within cells in the lining of the gutdigestion – within cells in the lining of the gut


BehaviorBehavior•Lack brain and true nervesLack brain and true nerves

•Nerve cells interconnect forming nerve net that transmits Nerve cells interconnect forming nerve net that transmits impulses in all directionsimpulses in all directions

•Sea anemones can tell if other member is from same cloneSea anemones can tell if other member is from same clone– Known to attack and even kill anemones from other clones Known to attack and even kill anemones from other clones


BehaviorBehavior•Some medusae have primitive eyesSome medusae have primitive eyes

•Medusae have Medusae have statocystsstatocysts, small calcareous bodies in fluid-filled , small calcareous bodies in fluid-filled chambers surrounded by sensitive hairs, to help with balancechambers surrounded by sensitive hairs, to help with balance


1. 1. PolypPolyp: a sac-like attached : a sac-like attached stage with a mouth and stage with a mouth and tentacles (mostly sessile)tentacles (mostly sessile)

2. 2. MedusaMedusa: a mobile bell-like : a mobile bell-like upside down polyp upside down polyp (jellyfish).(jellyfish).


• Larva is called Larva is called planulaplanula, ciliated stage with two cell layers, ciliated stage with two cell layers– Settles and metamorphoses into a polyp or develops into medusaSettles and metamorphoses into a polyp or develops into medusa


• Two layer of cells form body wall; one is epidermis (“skin”) Two layer of cells form body wall; one is epidermis (“skin”) and other is gastrodermis (gut lining)and other is gastrodermis (gut lining)

• Gelatinous middle layer is Gelatinous middle layer is mesogleamesoglea, does not contain cells, does not contain cells– In medusa this layer expands to form gelatinous domed In medusa this layer expands to form gelatinous domed

bellbell

Types of CnidariaTypes of Cnidaria

Sea fanSea fan

Cnidaria come in all shapes and sizes.Cnidaria come in all shapes and sizes.

•Hydrozoans- feathery hydroidsHydrozoans- feathery hydroids

•Scyphozoans- large jellyfishScyphozoans- large jellyfish

•Anthozoan-sea anemones and coralAnthozoan-sea anemones and coral

•Most of the animals found within Cnidaria are all carnivores.Most of the animals found within Cnidaria are all carnivores.

Cnidarian TypesCnidarian Types

Hydrozoans (class Hydrozoa)Hydrozoans (class Hydrozoa)

•Feathery or bushy colonies of tiny polyps attached to pilings, Feathery or bushy colonies of tiny polyps attached to pilings, shells, seaweeds, and other surfacesshells, seaweeds, and other surfaces

•Polyps may be specialized for feeding, defense, or reproductionPolyps may be specialized for feeding, defense, or reproduction

•Reproductive polyps produce minute, planktonic medusaeReproductive polyps produce minute, planktonic medusae


Hydrozoans (class Hydrozoa)Hydrozoans (class Hydrozoa)•Medusae release gametes & fertilized eggs develop into free Medusae release gametes & fertilized eggs develop into free swimming planula larvaeswimming planula larvae

•Each planula larvae settles and develops into a polypEach planula larvae settles and develops into a polyp

•The poylp divides repeatedly and develops into a colonyThe poylp divides repeatedly and develops into a colony

•Some lack poylp stage and develop into a medusaeSome lack poylp stage and develop into a medusae

•Few lack medusae stage and develop into gamete producing Few lack medusae stage and develop into gamete producing polypspolyps


Scyphozoans (class Scyphozoa)Scyphozoans (class Scyphozoa)•Larger jellyfishLarger jellyfish

•Large medusae are dominate stage in life cycleLarge medusae are dominate stage in life cycle

•Polyps small & release juvenile medusaePolyps small & release juvenile medusae

•Few lack polyp stageFew lack polyp stage

•Bell diameter ranges from 2-3 meters, depending on water Bell diameter ranges from 2-3 meters, depending on water depthdepth


Scyphozoans (class Scyphozoa)Scyphozoans (class Scyphozoa)•Swim with rhythmic contractions of bell but easily carried by Swim with rhythmic contractions of bell but easily carried by currentscurrents

•Some species stings range from rash to fatalitiesSome species stings range from rash to fatalities

•Cubomedusae once classified as Scyphozoa now in own class Cubomedusae once classified as Scyphozoa now in own class Cubozoa (box jelly)Cubozoa (box jelly)


Anthozoans (class Anthozoa)Anthozoans (class Anthozoa)•Anemones and coralsAnemones and corals•Solitary or colonial polyps that lack medusae stageSolitary or colonial polyps that lack medusae stage•Largest number of speciesLargest number of species•Polyps are more complexPolyps are more complex

– Gut contain Gut contain septasepta increasing surface area for digestion of increasing surface area for digestion of large preylarge prey

– Septa provide support for larger speciesSepta provide support for larger species•Sea anemones have large polypsSea anemones have large polyps


Anthozoans (class Anthozoa)Anthozoans (class Anthozoa)•Corals – colonial anthozoansCorals – colonial anthozoans•Carbonate skeletonsCarbonate skeletons•Occur in cold waters; tropical waters form reefsOccur in cold waters; tropical waters form reefs•GorgoniansGorgonians (sea fans) secrete branching skeleton made of (sea fans) secrete branching skeleton made of proteinprotein

– Precious corals Precious corals gorgonians are fused with red or pink gorgonians are fused with red or pink calcareous spicules in addition to protein skeletonscalcareous spicules in addition to protein skeletons


Anthozoans (class Anthozoa)Anthozoans (class Anthozoa)•Black Corals secrete hard, black protein skeletonBlack Corals secrete hard, black protein skeleton

•Used for jewelryUsed for jewelry

3. Comb jellies: Ctenophora3. Comb jellies: Ctenophora

Similar to cnidarians in most respects.

Nearly 100 spp.- all marine

Contain ciliary combs which assist in prey capture and mobility.


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?http://www.youtube.com/watch?v=G7WT81ukHZEv=G7WT81ukHZE


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

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2. Cnidarians