I. Protochordates (Tunicates, Lancelets) Marine Chordates: I. Protochordates (Tunicates, Lancelets)

The name Protochordates literally means 'the first chordates The name Protochordates literally means 'the first chordates.' The chordates include fish, amphibians, reptiles, birds and mammals. The protochordates fall into two broad groups or subphyla - the Urochordata and the Cephalochordata.

Urochordata The urochordata includes the group known as the tunicates - animals whose free-swimming larvae have a notochord and a nerve chord. The adults are sessile - they are anchored to one place on the Reef. Sea squirts are characterised by: having a hollow body with two openings being found either alone (solitary) or in colonies being attached to a reef

Sea squirts date back at least 500 to 600 million years Sea squirts date back at least 500 to 600 million years. They have very advanced body structures and belong to the same Phylum as humans (Chordata). Their larval stage looks very similar to a tadpole, complete with rod cells (notochords) running down their backs just like those of embryonic vertebrates.

Adult Sea Squirt Sea Squirt Larvae Notocord

Cephalochordata Cephalochordates, or lancelets, are fish-like animals that have a notochord and nerve chord along the entire length of their bodies and which persist all their lives. Although they can swim fairly well, most animals are found with their tails buried in the sand with only the anterior end protruding.  Like the tunicates, lancelets are filter feeders. 

They take in food and water through an oral hood whose edges bear delicate projections called cirri that act as a strainer to exclude larger objects.  Inside of the oral hood are bands of cilia that sweep food into the mouth.