Is fucus filamentous or colonial algea?
I would suggest looking up some basic sources on types of algae. For example, that source that I link to says this:

Algae vary considerably in size, shape, and growth form.
They can be:

Single celled
Many celled - either colonially or as filaments of cells; or
Elaborate plant bodies with differentiated cell types


In this case, I believe that Fucus would be in the third category (&quot;elaborate plant bodies&quot;).
But note that these are informal categories, they don't really correspond to taxonomy or evolution or anything.