Invertebrate Chordates

Invertebrate chordates are a special type of animal. They belong to the phylum Chordata (having a hollow dorsal nerve cord), yet they lack supporting or protective structures for their nerve cords and brains—they've got no bones!

Members in this group belong to the subphyla (some may say classes) Urochordata and Cephalochordata.

Urochordata

Urochordates (also called tunicates) are animals like the salps or sea squirts. These animals possess a dorsal nerve cord only in their larval stage, when they are free-swimming and exhibit bilateral symmetry—as adults, most are sessile, meaning they stay attached to one place for their entire lives, as coral does, although salps live in free-floating colonies. Adult tunicates no longer exhibit bilateral symmetry.

Stalked tunicates. NOAA

Colonial orange tunicates. NOAA

Salp Colony. NOAA

A tunicate tadpole, or larva. BIODIDAC, © Houseman

Cephalochordata

An example of an animal in this group are the lancelets. These are small, almost fish-like or eel-like animals with definite heads, but no fins or bones. They spend most of their lives half-buried in the sand filtering food from the water.

Lancelet. Dr. M.D. Stokes