Jellyfish
The Jellyfish, unlike most other animals, does not possess any excretory organs. Rather than having a separate mouth and anus, it uses a single multipurpose orifface. This system of excretion is known as an incomplete digestive system. The single excretory orriface is known as a coelenteron. This cavity both processes the jellyfish's food by means of extracellular digestion (digestion of food outside of individual cells) and expels it out.
Sea Anenome
The Sea Anenome is a long living cnidaria that, like the Jellyfish, does not have an excretory system. This animal excretes by releasing waste from its gastrovascular cavity and out of its slit-like coelenteron, which is located on top of the sea anenome's body.
Portuguese Man 'O War
The Portuguese Man 'O War is also a member of the phylum Cnidaria . The Portuguesee Man O' War is a siphonopore (multiple organisms that cohesively act as a single body) that also lacks an excretory system. It paralyzes its prey and absorbs its nutrients, and releases the waste produced through its outer membrane.