BIOL 111 Lecture Notes - Lecture 60: Cnidaria, Gastrulation, Mitosis
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BIOL 111 – Organismal Biology
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!!coral atolls form when a large volcano collapses in the water
!!coral bleaching is occurring due to pollution
•!zooxanthellates are being expelled
•!are negatively affected by temperature and UV increases, pollution,
and disease/bacteria
•!hydrozoans
o!polyp phase is dominant, but most species alternate between polyp and medusa
o!an example is Hydra
!!a freshwater organism
!!has no medusa stage
!!basal disk acts like a foot
!!moves by gliding (basal disk secretes mucous), somersaulting or floating
(basal disk release a bubble of CO2)
!!are 2-5 mm in length
o!another example Portuguese man-of-war
!!are colonial
!!are both polyps and medusa
!!float due to gas-filled interior
!!live in tropical and sub-tropical oceans
Cnidarian Reproduction
•!through mitosis, a polyp may produce a medusa and release it
•!medusa releases either sperm or egg into the water where fertilization can occur
•!upon fertilization, cleavage and gastrulation occurs to produce mature embryo, which in
turn becomes a larva (immature form of an animal)
•!larva undergoes mitosis to become polyp
•!asexual reproduction can also occur by budding
Types of Body Symmetry
•!asymmetry – no axis divides body into equal halves
o!e.g. sponges
•!radial symmetry – central axis divides body into many equal halves