BIOL 111 Lecture Notes - Yolk Sac, Osmotic Concentration, Ovoviviparity

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~ 53000 speices = very diverse
- Include the vertebrates
- Deuterostomes
- Coelomates
- Bilateral symmetry
3 unique characteristics:
1. Dorsal hollow nerve cord
2. Notochord: supportive rod internally (highly reduced in vertebrates,
replaced by spine)
3. Post-anal tail
Other characteristics:
1. Pharyngeal slits: found in chordates but not unique to them: seen first in
2. Hollow dorsal nerve cord and segmentation is formed by neurulation
3. Central heart
4. Reduced segmentation
5. Segmented musculature
- myomeres
Deuterostomes include chordates
Pharyngeal slits:
- Pouches in human embryo
- Located on lateral surface of head
- In all vertebrates, ancestral trait in deuterostomes
- In vertebrates: are supported by arches: what become jaws and are
important for gas exchange
- For Filter feeding
- For respiration in vertebrates: water coming in mouth passes through slits
- O2 and CO2 can be exchanged across a respiratory surface = gills
- Supported by gill arches
Gills: bars in between the slits = gill arches
- made of bone or cartilage
- gill filaments on gill arches: respiratory exchange takes place
- In boney fishes: 4 pairs of gill arches
- Pairs of filaments down the filaments
- Gill raker: strained food, prevents food from exiting mouth through
- Covered by operculum, protects gills
- Gills full of vascular tissue
- Filament structure:
= thin, vascularized, high surface area, moist, maintain partial pressure
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