Chordates - Chordata

I am not sure my wife is all that happy about being included in the marine fauna, but I just wanted to make a point of the fact that humans belong to the phylum Chordata.

At some stage in their life cycle, chordates have a pair of gills or similar organs to extract oxygen from a liquid environment. In our case, lungs replace rudimentary gill slits after the embryonic stage. As you know, fish keep their gills for the rest of their lives.

Chordates also have a notochord (spine in our case) at a certain stage in their life span. The spinal chord of ascidians degenerate at a certain phase. Humans and other vertebrates replace the notochord with a more complex skeleton structure during the embryonic stage.

The two largest classes of fish are the cartilaginous fish (including for instance sharks, skates and rays) and the bony fish including most other commonly known fish species.