Cnidaria
Cnidarians, are mainly jelly fish animals that have a one way digestive system, which means eating and execrations occurs through the same opening. This is also known as a gastrovasular cavity.Cnidarians are usually predators and use their nematocysts to inject venom into their prey. Cnidos is the Greek term for stinging needle, which is why jelly fish are called cnidarians.
coral
Coral are examples of sea anemones and they only have one opening for feeding and dispensing waste. they are nocturnal feeders. Coral is surrounded with tentacles to stick to surfaces and stick to their food as well. The tentacles are full of nematocysts, which help to paralyze their prey and bring it towards their mouths. Inside the stomach cavity there is mucus which helps with digestion, and what ever is left is excreted through mouth.
siphonophores
Siphonophores are another deep water species belonging to the Cnidaria family. These Siphonophores are compound organisms made up of the same stinging cells, nematocysts, to paralyze their prey before eating. The interesting twist about the Siphonophores, is that they each individually have a little light of a different color to first attract prey close enough for the nematocysts to sting them. These are called their bioluminescent lights, and they can flicker on and off to attract prey. They then bring food down to the digestive tract and the waste proceeds out the same end.
portuguese man o' war
The portuguese man o' war is another Cnidaria and is also a Siphonophora. It is apart of the Physaliidae family. It's class is a Hydrozoa, as it it often mistaken for a jelly fish. Unlike the other animals previously discussed, they cannot use speed or surprise attacks due to the movement of the waves in the sea and because their body is very malleable. They instead go all out and stretch out all their stinging tentacles into a floating net. The net has a pigment that resembles habitats for their prey such as coral cove oral rival fish, to attract here prey. When the get caught, portuguese man o' war contracts it's tentacles to bring it up to the mouth and begins to secrete digestive enzymes to liquefy the prey.