Without the specimens it is not so easy to tell but it looks similar to a phorinid.  I have found something not unlike this subtidally in shallow water in Ireland.

Thanks Paul, Yes I was side-tracked by the large lophophores.

Thanks for all answers! I agree that this is a Flustrellidra hispida after comparing it with description of its morphology and pictures on google.

An additional question: I have never encountered this species before, despite extensive cruises and field expeditions in northern Norway. How common is this species this far North (ca 69⁰ N)?

This species grows on algae indeed. For questions on ID of Bryozoa you may also consult the Facebook group on NE Atlantic Bryozoa. 

https://www.facebook.com/groups/133129276808670/

Flustrellidra hispida - no question.