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Phyllodiscus is a monotypic genus of sea anemones in the family Aliciidae. The only species is Phyllodiscus semoni, commonly known as the night anemone, which is native to shallow seas in the central Indo-West Pacific, such as Indonesia, the Philippines and southern Japan. It is venomous and can cause a painful, long-lasting sting to humans. It is called unbachi-isoginchaku in Japanese which translates as "wasp-sea anemone".

Phyllodiscus semoni has a broad basal disc attached to the substrate. The lower portion of the column is smooth and the middle section has a radially arranged series of pseudo-tentacles, thick, stalked and branched outgrowths which show great variety in their appearance between different individuals. There are a number of hemispherical vesicles on the branches, and occasionally on the stalks. These contain nematocysts containing short and long-shafted stinging threads. The upper section of the column is short and smooth with a few nematocysts. The oral disc has a marginal ring of up to 160 long tentacles, two siphonoglyphs (feeding grooves) and a central mouth.