A plural or variant form referring to a group of marine animals that includes jellyfish, corals, and sea anemones.
From Greek 'koilos' (hollow) + 'enteron' (intestine), referring to these animals' simple hollow body cavity that serves as a stomach and intestine combined.
Jellyfish and corals have one opening for both eating and pooping because their body is basically just a hollow tube—nature's simplest recycling system.
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