Colpomenia peregrina, sometimes referred to by its vernacular names oyster thief and bladder weed,[1] is a species of brown seaweed.

peregrina Sauvageau) is a small brown alga, bladder-like, hollow and membranous, up to 9 cm across.

C. sinuosa was present at least as far back as the 1840s in Spain, and C.peregrina was introduced and first noticed by oyster fishermen in the Bay of Biscay in 1906.

It is globose and smooth when young, becoming hollow and convoluted with age and growing to 5 cm in diameter.

[9] This species is found in littoral rock pools, in localities that are not exposed, and also in the sublittoral to a depth of 3m.

Colpomenia peregrina has been recorded in Ireland from the following counties: Down,[13] Donegal,[4] Kerry, Galway, Clare and Cork.

C. peregrina is found in intertidal to subtidal zones of the coasts of the North and South Islands.