Acoel flatworm on corals (Waminoa sp.) care guide

Group
Other invertebrates
Other names
Waminoa flatworm, Acoel flatworm, Waminoa litus, Waminoa brickneri, Coral flatworm
Family
Convolutidae
Origin
Coral reefs of the Red Sea, Indonesia and Australia; arrives on coral frags
Water
saltwater
Reef safe
no

Care

Waminoa are tiny, flat, oval to round acoel flatworms, usually only a few millimetres across, that sit on the surface of living corals, often in large numbers. They are translucent brown or tan with paler spots, because they carry two kinds of symbiotic algae (Symbiodinium and Amphidinium). Two species are known, W. litus and W. brickneri. They are not the red planaria (Convolutriloba retrogemma), which forms rust-red carpets on rock and sand, nor the Acropora-eating flatworm. How it arrives: on coral frags and colonies, especially soft corals, bubble corals, Euphyllia and other large-polyped corals. It is usually overlooked because it blends in with the coral. How to identify it: look for many small, flat, brownish discs, often with paler centres, spread over the coral surface; they slide away when the coral is moved or blown with a pipette. Harm done: the worms feed on coral mucus and, in large numbers, cover the coral, shading it from light and irritating it, so it stays closed and may decline. Removal and prevention: quarantine new corals and dip them in a reef coral dip, blowing the coral surface with a turkey baster or pipette to dislodge the worms, then siphon them out. Repeat dips may be needed. Some wrasses (six-line, leopard and melanurus wrasses) and some dragonets may pick at flatworms. This is a pest and should not be sold as livestock. Copper: copper-based medicines and some plant fertilisers are toxic to shrimp, snails and most other invertebrates. Never dose them in a tank holding this animal, and check the label of any treatment or fertiliser before use. Sources: Wikipedia (en.wikipedia.org/wiki/Waminoa). Checked October 2026.

Diet

Feeds on coral mucus, with extra food from its symbiotic algae.

Breeding

Reproduces on its host coral, and numbers can build up quickly in aquaria. The symbiotic algae are passed from mother to offspring. Our sources do not describe its reproduction in more detail.

Compatibility and tank mates

Pest. Lives on corals and weakens them by covering and shading their tissue. Harmless to fish. Some wrasses and dragonets may eat it.

Last updated 8 October 2026. Community-edited care guide on Aquatic-Auctions.

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