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