Flatworms

Platyhelminthes

Flatworms of the phylum Platyhelminthes - mostly free-living polyclads gliding over reefs in striking colour patterns.

Last updated May 2026

Pink flatwormProstheceraeus roseus16 photos

Up to 4 cm3–30mRocky reef

A pale pink to rose-colored marine flatworm with a smooth, oval body and wavy edges. Similar to the pink flatworm but more uniformly colored.

Found under stones and in shaded crevices — slides gracefully over rocky surfaces, nearly transparent in bright light.

Observed at

Bajo Piles I(Cabo de Palos)El negre(Costa del Maresme)Punta Cana(Costa del Maresme)Pedra de Déu(Illes Medes)Ancora del Negre(Costa del Maresme)La Calzada(Costa del Maresme)El Trencat(Costa del Maresme)Ferranelles(Illes Medes)Els Canons de Tamariu(Begur)La Virgen(Costa del Maresme)El Santuari(Costa del Maresme)

Brown flatwormYungia aurantiaca4 photos

Up to 6 cm2–30mRocky reef

A flat, oval marine flatworm (not a true nudibranch) with a velvety brown surface, often with lighter margins. Paper-thin and remarkably flexible.

Glides over rocky surfaces and under stones — can swim briefly by undulating its body edges like a magic carpet.

Observed at

Pedra de Déu(Illes Medes)

Candy-striped flatwormProstheceraeus vittatus4 photos

Up to 5 cm1–30mRocky reef

A polyclad flatworm (not a true nudibranch) with a cream body finely lined with dark longitudinal stripes and a delicate ruffled margin. Two raised pseudotentacles mark its leading edge as it glides over rock with smooth, undulating motion.

Observed at

Bajo de Dentro(Cabo de Palos)Bajo Piles I(Cabo de Palos)

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