Cnidarians

Increasing Success of the Jellyfish

• Loss of consumers: Sea turtles, sunfish

• Climate change: Warmer waters increase metabolic rate and thus speed growth and reproduction rates

• Nutrient pollution: Increases phytoplankton growth that feeds jellies

Decreasing success of the Corals

• Loss of consumers: Herbivorous fish that clean corals of macroalgae

• Climate change: Warmer waters increases susceptibility to disease, leads to loss of zooxanthellae (bleaching)

• Nutrient pollution: Stimulates macroalgal growth

• Overfishing

• Land-based runoff and pollutant discharges.

• Carbon dioxide emission

• Several diseases (viral and bacteria) infect coral. Come from human waste.

Major evolutionary advances seen for first time in cnidarians

-          Tissue level of organization

-          Nervous system development

-          Muscular Movement

-          Photoreceptors

-          Gut Cavity

-          Hydrostatic skeleton

Pigment Spot ocellus

§  Sense light, but no direction

§  Associated with integument

Inverted pigment cup ocellus

§  Sense light and direction

§  Pigment blocks light, only passage through opening

Cnidocyte

Cell

Cnidae

stinging organelle inside cnidocyte

Nematocyst

most common type of cnidae

General Morphology of Nematocyst

Primarily on tentacles, around mouth, gastrovascular cavity

Predation, Defense, Fight against their own type

Where Nematocyst are used

Firing of Nematocysts

• Stimuli received

• Sudden release of Ca2+ into interior of nematocyst

• Water rushes in due to osmotic pressure

• Pressure rises inside capsule

• Operculum opens

• Tube everts (turns inside out)

• Stylets punctures prey and then flip back

• Thread injects into prey through hole created by stylets

• Total process takes 3 ms

Class Hydrozoa

o    Generally small

o    Plantlike appearance

o    Have vellums. Constrict the opening, giving them more propulsion.

o    Portuguese man of War

Valella Vallela

• Go really deep down the ocean and the top of the ocean.

• Dinoflagellates have a symbiotic relationship.

• Hydrozoa

Hydrocorals (fire corals)

§  Calcareous skeleton

§  Zoids emerge from pores

Class Scyphozoa

o    Gametes lodge on oral arms.

o    Does not have vellums.

o    Normal Jellyfish 

Class Cubozoa

§  Medusa dominant

§  Virulent toxins that can be extremely dangerous

Sense Organs of Class Cubozoa

§  Complex eyes (8 image forming eyes, 24 eyes total)

§  Lens

§  Retina-like arrangement of sensory cells

§  Allow image formation

§  The reason why of the image formation is for mating.

§  Gastrodermal glands

§  Evolved independently of eyes in rest of cnidarians

Multiple kinds of eyes of Class Cubozoa

§  Upper lens eye looks up; lower lens eye looks horizontally

·         Can form images (blurry images)

§  Pit eyes and slit eyes

·         Cannot form images, just sense light

·         Image forming eye not connected to brain (remember only nerve net)

·         Round lens provides clear image, but focal plane is off, so image is blurry

·         Visual output is channeled directly to the pacemaker for swimming movement, also located in rhopalium

Irukankji Syndrome

Box Jellyfish

Class Anthozoa

§  Acrorhagi: Aggression towards other clones or species

§  Cnidocytes fire at “foreign” anemones

§  Special fighting tentacles: acrorhagi

§  Forms separation between species or clones

Corals

·         Calcium carbonate (CaCO3) skeleton (external)

·         Polyp structure very similar to that of anemones

·         Feeding similar to that of anemones

·         Form colonies that are all connected by sheet of tissue

General pattern of complex life history

Larvae, Polyp, Medusa