What are the differences between the manga and anime versions of Excel Saga? How does the anime for Excel Saga differ from the manga? More specifically, does the plot in the Excel Saga anime depart significantly from that in the manga?

I've read that some characters only appear in the anime. What are notable differences between the characters who appear in the manga and those who appear in the anime? Are there any other differences? Is the structure of the anime (i.e. one episode spoofs of different genres) different from that of the manga or are there similarities?
I've only read a bit of the manga, but as far as I can tell, the manga was more of a focused satire on the state of Japan's economy and politics in the '90s and early 2000s (a bit more like the later, similar series Nerima Daikon Brothers). It didn't have as much genre parody as the anime did. It also had the character of Elgala, a third ACROSS agent who works alongside Excel and Hyatt.