Cats and dogs aren’t even species; they’re vague categories. I tried to find the actual answer to this question, but trying to nail down individual species is proving impossible. Every source is like “copepods” or “ants” like that isn’t incredibly broad. ChatGPT says it’s the Antarctic krill with 5x10^14 individuals. Going from there, the WWF says there’s over 7x10^14, and Wikipedia only says they’re one of the most abundant species, but not the most. I’m not going to get an answer to this question, and I’m going to be mildly annoyed about it infrequently for the rest of time.