Porphyra linearis, pictured above, is a multicellular red algae that grows in a flat sheet or blade form. This is a small species of algae, generally less than an inch long. It is most visible in the winter and often grows in the same community as the filamentous algal species in the upper intertidal zone. The difference between Porphyra and the filamentous seaweeds is that Porphyra has a holdfast. Can you identify the holdfast on this specimen? Click on the picture to see if you are right.