X is for Xanthodont:
Yellow-toothed. Yes, the teeth are supposed to be that colour. Many rodents have yellow teeth, Syrian hamsters for example. This is a Coypu and you can get an even closer look at the teeth here
X is also for Xiphosuran - an order of animals that contains for example horseshoe crabs:
Horseshoe crabs are not crabs, not even crustaceans. They are more related to arachnids, but really they are doing their own thing and have been doing it for a very long time - for the last 450 million years.
See what else X stands for with ABC Wednesday
Photos were taken at Wildpark Schwarze Berge Hamburg, Hagenbecks Tierpark Hamburg and Oregon Coast Aquarium.