Urochordates (tunicates)

The pharynx is lined with a mucus net that filters seawater.  The tunic is made up of cellulose-like carbohydrates.  Tunicate larva is a free-swimming suspension feeder with all four chordate characteristics.  The tunicate adult is sessile (anchored) with only the pharyngeal slits.

Cephalochordates (lancelets)

Lancelets swim in a sinusoidal pattern ( ~ ~ ~ ~ ~ ).  Muscle segments develop from mesoderm blocks on both sides of the notochord.  These blocks are called somites.

Next:  "Phylogeny."