Jellyfish are amazing creatures with unusual characteristics.
They're 98% water and are seemingly majestic animals with their elegant movement through the ocean's water, but they also harbour one of strangest attributes of all: their mouth is also their pooper.
However unusual this seems to us, it has evolved to serve the jellyfish perfectly for its bodily functions. It's simply down to how their body and digestive tracts are built.
As a unique and highly evolved, yet simple ocean dwelling creature, the jellyfish doesn't have to worry about hygiene the same way that most other creatures do.
Here's a diagram of the jellyfish's layout from HowStuffWorks: