While solving this cryptic I figured out the answer to 1-across (mammal sounds like relative consumer) without solving the subsidiary indication. (I used down constraints and the standard part of the clue to guess the right answer.) After confirming my answer in the solution (warning: spoiler) here, I am even more baffled as to how the subsidiary was supposed to work. Please help!
"sounds like relative" refers to ant (aunt), so the clue is "ant consumer," which is an AARDVARK by ddef.
I see this as being
relative = aunt = (sounds like) ant and consumer = eater giving anteater which is an alternative name for aardvark.
Interestingly enough, this would actually fit as it is and is what I would have put down on first seeing the puzzle. This would have given me a lot of headaches with 2,3 and 4 down later!