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ChordatesCharacteristics that Unify this
Group: 1. Notochord 2. Hollow, dorsal nerve cord3. 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