Acoela | |
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Many flatworm-like, orange individuals of the Waminoa acoel on a Plerogyra coral (whitish bubbles) | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Xenacoelomorpha |
Subphylum: | Acoelomorpha |
Order: | Acoela Uljanin, 1870 |
Acoela, or the acoels, is an order of small and simple invertebrates in the subphylum Acoelomorpha of phylum Xenacoelomorpha, a deep branching bilaterian group of animals, which resemble flatworms. Historically they were treated as an order of turbellarian flatworms.[1][2] About 400 species are known, but probably many more not yet described.[3]
The etymology of "acoel" is from the Ancient Greek words ἀ (a), the alpha privative, expressing negation or absence, and κοιλία (koilía), meaning "cavity".[4][5] This refers to the fact that acoels have a structure lacking a fluid-filled body cavity.