INTRODUCTION TO CHORDATES:
5 chordate hallmarks:
Notochord:
A flexible rod, extending the length of the body
It is the first part of the endoskeleton to appear in an embryo
It is a hydrostatic organ
Muscles attach to the notochord, and because it can bend laterally without shortening, it permits
undulatory movements of the body
Dorsal tubular nerve cord:
Single nerve cord is dorsal to the digestive tract and is a tube
The anterior end becomes enlarged to form the brain
The hollow cord is produced in the embryo by infolding of ectodermal cells on the
dorsal side of the body above the notochord
Pharyngeal pouches and slits:
Pharyngeal slits are openings that lead from the pharyngeal cavity to the outside
They are formed by inpocketing of the outside ectoderm (pharyngeal grooves) and
evagination/outpocketing of the endodermal lining of the pharynx (pharyngeal
pouches)
The perforated pharynx evolved as a filter-feeder apparatus. Water with suspended food particles is drawn
by ciliary action through the mouth and flows out through pharyngeal slits where food is trapped in mucus
Endostyle or thyroid gland:
Located in the pharyngeal floor, it secretes mucus that traps food particles brought into the pharyngeal
cavity
Some cells in the endostyle secrete iodinated proteins
Postanal tail:
A postanal tail, together with somatic musculature and the stiffening notochord, provides the motility used
for free-swimming
It has evolved for propulsion of water
5 chordate hallmarks:
Notochord:
A flexible rod, extending the length of the body
It is the first part of the endoskeleton to appear in an embryo
It is a hydrostatic organ
Muscles attach to the notochord, and because it can bend laterally without shortening, it permits
undulatory movements of the body
Dorsal tubular nerve cord:
Single nerve cord is dorsal to the digestive tract and is a tube
The anterior end becomes enlarged to form the brain
The hollow cord is produced in the embryo by infolding of ectodermal cells on the
dorsal side of the body above the notochord
Pharyngeal pouches and slits:
Pharyngeal slits are openings that lead from the pharyngeal cavity to the outside
They are formed by inpocketing of the outside ectoderm (pharyngeal grooves) and
evagination/outpocketing of the endodermal lining of the pharynx (pharyngeal
pouches)
The perforated pharynx evolved as a filter-feeder apparatus. Water with suspended food particles is drawn
by ciliary action through the mouth and flows out through pharyngeal slits where food is trapped in mucus
Endostyle or thyroid gland:
Located in the pharyngeal floor, it secretes mucus that traps food particles brought into the pharyngeal
cavity
Some cells in the endostyle secrete iodinated proteins
Postanal tail:
A postanal tail, together with somatic musculature and the stiffening notochord, provides the motility used
for free-swimming
It has evolved for propulsion of water
