Chordates Characteristics that Unify this Group: Notochord Hollow, dorsal nerve cord 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