Phylum Cnidaria

Phylum Cnidaria

1. Characteristics

   • Multicellular
   • Have true tissues
     • Two tissue layers
       • Diploblastic
         • Epidermis(ectoderm)/ Gastrodermis(endoderm)
           • Mesoglea, extracellular matrix, between layers
     • Two morphological forms
       • Polyp
       • Medusa/ Jellyfish
   • Radial symmetry
     • Oral/ aboral ends
       • No definit head
   • Marine/ Aquatic
   • Sessile or free moving

2. Body structure

   • Mouth/ anus/ tentacles/gastrovascular cavity/ gastrodermis/ mesoglea/ epidermis
     • Polyp
       • Cylindrical/tubular
     • Medusa
       • Umbrella/bell

3. Life cycle

   • Poly/ medusa/ both
     • Sea anemone: polyp
       • Polyp: rapid increase in number/ sessile and maintain in favourable enviro
     • Jellyfish: medusa
       • Spread out/ Genetic variation/ New habitat
     • Wide range of habitat
       • Benthnic(bottom) and pelagic(open water)
   • Life cycle of a Obelia ( Class hydrozoa)
     • Fertilization/ Zygote/ planula(larvae, ciliated)/ polyp(pedal disc on the aboral end) / asexual reproduction (budding)/ Colony of polyp(clone, different gene expression, differentiated functions) ( feeding polyp, reproductive~), medusa bud, medusa, gonads produce egg+sperm

4. Feeding and digestion

   • Tentacles to capture prey
     • Cnidocyte on tentacle
       • Nematocyst (organelle)
         • Sting: Capture and immobolize
           • Spines and barbs on stings
           • Triggered by stimulation. Water permeability increases in cnidocyte, P builds up
           • Pierce, inject venom
   • Extracellular digestion by enzymes, Intracellular digestion for complete digestion
   • Two way gut

5. Hard corals

   • Polyp stage only
     • Polyps secrete corallite for anchorage and protection
   • Mutualistic relationship
     • Algae and corals
       • Heterotroph/ autotroph
         • coral bleaching
   • coral spawning
     • No medusa stage/ polyp produces gamete