Don't worry too much about it. If you take a look at the number of questions on the DAT, Diversity of Life is literally only a tiny part of all biology tested, yet the amount of energy you need to know it through and through is disproportionately high. I would recommend you print out the DAT bootcamp chart ( or any comparable chart where you can read about the main inferences between all the phyla), and just try to familiarize with a little every day over a month or so. I honestly didn't really study it at all like anything else, and the one question I got was super easy: something like which of the following is a pseudocoel or something like that. Like the above poster, it's not going to be that involved I don't think that you will have to recall everything possible about every phylum.