Difference between unclassified and unknown clade in metaphlan3

Hi!

I am using metaphlan3 for metagenomics analysis on colorectal samples. Some samples result in a lot of taxa and some don’t. At the moment I am reading online about how the ‘unclassified’ and ‘unknown’ clades are generated. I was wondering if there are any differences of the meaning ‘unclassified’ and ‘unknown’.

Kind regards,

Moelong Yu