Below is the definition of therewithal according to google and several other sources.
Therewithal: together with that; besides. "he was to make a voyage and his fortune therewithal"
I was searching for a proper antonym for the word, such as "therewithout" (sadly it's not a real word), yet couldn't find anything. The sentence I'm trying to compose is as follows:
"In order to observe if these isopods would discriminate between environments with soil and other terrestrial environments (therewithout)..."