動物: dôbutsu. The Japanese make a crucial distinction between "animal" (dôbutsu) and "bug" (mushi)—the latter category including insects, arachnids, worms, parasites, and other wiggly, slimy critters. So, in a short renku there's no reason not to have both kinds of creatures: bunnies and ants, birds and worms, dinosaurs and spiders.
When you're brainstorming animals to include in your renku, some major categories to think of are four-footed (四つ足), bugs (虫), birds (鳥), and fish (魚). But all creatures count, from whales to bacteria.