Colpomenia peregrina Sauvageau

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Common names: Oyster Thief, Bladder Weed; Ballons, Voleuse d'huîtres.
Description: Plants baloon-like when young, becoming contorted and collapsed with age, brown when young to yellow-brown when older, generally 30-90 mm, but up to 250 mm. Frond thin, papery, delicate, and filled with seawater when young, hollow and empty when older.
Habitat: Generally growing epiphytically on Corallina officinalis and other algae, and on mussels and oysters. It most obvious in spring, reaching its maximum size in May in Ireland.
Key characteristics: Not solid and gelatinous like Leathesia marina, which persists all year around although it most obvious in summer.
Note: An introduced species, perhaps by means of shellfish movements. Plants are said to inflate with gas and to float away with small oysters; thus the common name.

Identification guide for selected marine non-native species (National Museum Wales). (Download free PDF, about 3.5 Mb).

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