Green colored seaweed that can reach 20 to 200 millimeters long, composed of several blades or tubes that arise from a common attachment point. There are two different growth forms: one has a compressed shape, narrow sheet with ruffled edges, and the other (commonly referred to as Enteromorpha compressa) possesses hollow fronds rounded at the top, often with bubbles of oxygen (from photosynthesis). The tissue of both forms has a thickness of just one cell. It's habitat includes tide pools, sandy rocks, rocks in the intertidal and shallow subtidal up to 3 meters deep. Ulva compressa is extremely tolerant to widely varying salinities, temperatures and ph.

References:

http://macoi.ci.uc.pt/spec_list_detail.php?spec_id=168

http://www.seaweed.ie/descriptions/ulva_compressa.php