Chordates
Characteristics that Unify this
Group:
1. Notochord
2. Hollow, dorsal nerve cord
3. Pharyngeal slits
Chordate Characteristics
Notochords
• Long, flexible support
rod
• Dorsal, just below
nerve cord
• Usually replaced by
backbone in early
development
Hollow, Dorsal Nerve Cord
• Just below the
notochord
• Front end develops
into the brain
• Many nerves branch to
rest of body from this
main cord
Comparison of Arthropods and
Vertebrates
Pharyngeal Slits
• In aquatic chordates,
these develop into gill
slits
• Only chordates have
pharyngeal gill slits
Pharyngeal Slits
• In terrestrial chordates
the pharyngeal slits
close up at an early
stage in development
• In humans, the embryo
doesn’t ever develop
actual slits, but does
develop pharyngeal
“pouches”
Invertebrate Chordates –
Tunicates and Lancelets
Invertebrate Chordates –
Tunicates
Tunicates – Larvae and Adult
Tunicates - larva
• Tadpole-shaped
larvae are free
swimming.
• Only the larvae
have the
notochord and
dorsal nerve cord
• They Filter
plankton and
breathe through
their pharyngeal
gill slits
Tunicates - adults
• Adults develop
through
metamorphosis of
larval stage
• Are sessile, filter feed
and breathe through
the gill slits
Lancelets
• Fish-like shape
• Half (at least) of
their body is
buried in the sand
• Filter-feeders
• Have mouth and
up to 100
pharyngeal slits
along body
Lancelets
• Have
muscle/nerve
arrangement
similar to that
found in ALL
vertebrates
• No jaw
• No
appendages