BIO2231 Lecture Notes - Lecture 17: Dorsal Nerve Cord, Eustachian Tube, Aortic Arches
Lecture 17 - Chordates
Phylum Chordata
• Includes vertebrates
• Bilaterally symmetrical
• Dueterostome
o Radial and indeterminate – regulative
• Coelomates
Five major features
1. Notochord
2. Dorsal tubular nerve cord
3. Pharyngeal pouches and slits
4. Endostyle (thyroid gland)
5. Postanal tail
• Notochord
o Flexible rod of fluid-filled cells surrounded by a tough sheath
o Supportive rod that extends most of length of animal along dorsal body
wall
o Consists of connective tissue sheath packed with vacuolated cells
o Supports body along anterior-posterior axis
• Dorsal tubular nerve cord
o Anterior enlarged to form brain, cerebrospinal fluid in vertebrates
o Runs along dorsal axis of body above notochord
o Modified anteriorly into a brain
o Allowed development for sensory perception, integration and motor
responses
• Phrayngeal pouches and slits
o Slits between aortic arches
o Evagination of endodermal lining
o Invagination of ectoderm
o Connects pharynx to outside
o Series of openings between digestive tract in pharyngeal region and
outside of body
o Used for gas exchange
o Eustachian tube used in equalising pressure to prevent damage to ear
drum
• Endostyle (thyroid gland)
o Secretory furrow on pharyngeal floor
o Produces mucus
o Iodinated proteins
o Filter feeding apparatus
o Secretes mucus to trap food particles
• Postanal tail
o Tail, segmented body wall
o Somites
o Locomotory structure
o Extends posterior to anal opening
o Supported by notochord
• Pharynx > Gill slits > atrium
find more resources at oneclass.com
find more resources at oneclass.com
