Complex sentence: It begins with a general overview of ichthyology, although it is not a self-contained introduction, then after a short section on Chordata and non-fish taxa, the work goes on to list all known fish in a top-down fashion.
Split into simpler sentences: It begins with a general overview of ichthyology, although it is not self-contained. After a short section on Chordata and non-fish taxa, the work lists all known fish in a top-down fashion.