Well, according to BS01 (though I can't seem to find the source, so sue me):
"The original Krana were created by the Great Beings by exposing to Energized Protodermis the remains of the process that created the first Matoran. This procedure resulted not only in Krana, but also Zyglak.
The Bahrag were later taught how to create Krana on their own and were given Energized Protodermis to do so. A carving depicting the process the Bahrag used was inscribed on a tunnel above Metru Nui."
I wouldn't be surprised, I did remember reading that the creation of the Zyglak was a side-effect of the Krana being made by the Great Beings.