Biology 102Lecture 24Outline of Last Lecture:I. Clicker QuestionsII. TapewormsIII. RoundwormsIV. InsectsOutline of Current Lecture:I. Clicker QuestionsII. ChordatesClicker QuestionsAnimals with exoskeletons, such as insects, have to molt as they grow larger. This is because the exoskeletona. Isn’t a living tissueb. Can’t grow with the organismc. Will crack if it grows largerd. Both a and bMosquitoes undergo complete metamorphosis and there are more than 2,500 species of mosquitoes worldwide (150 in US). On the other, hand, ticks undergo incomplete metamorphosis. Moreover, there are only 500 species of ticks worldwide (90 in US) which of thetwo is more successful and why?a. Ticks are more successful because they are easily able to hide on the host’s body and they can feed they can then feed longer b. Mosquitos are more successful because they undergo complete metamorphosisc. Mosquitoes are more successful and this is because they feed on hosts that are higher up in the food chaind. Ticks are more successful because they undergo incomplete metamorphosis. The larval forms are already suited very well for the environment and thus they don’t have to change much to become an adult.ChordatesChordates: not all chordates are vertebrates- Chordates include vertebrates AND invertebrates- 4 Characteristics:1. Dorsal hollow nerve cord (in vertebrates think of it as a spine)Biology 1022. Flexible supportive notochord or rod (vertebral column)3. Pharyngeal slits (ex. fish have gills or a human embryo when its developing has slits to help it breathe)- Develop into different structures: gills, auditory cavity, sinus cavity4. Muscular post anal tailAll of these characteristics must occur at a certain point during the life cycle, they can happen atthe same time or at different times, but they all happen.Simple Chordates:- Tunicates: aka sea squirt- Stationary, don’t move, become sedentary and attach to a surface- Invertebrate chordate- First to have a brain- Lancelet: - Closest living non vertebrate relative to vertebrate- Invertebrate chordate- Hagfishes- First to develop a skull- Slime glands- Enters through any opening or attaches to the animal - If a fish swallows him he spits slime that fills the gills of the fish so the fish cant breathe and spits him out- Lampreys- Attach themselves to things - Oral discs as
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