What can you say?  This common name is another really descriptive one although all pictures I have seen of Neptune portray him with a full beard rather than a shaved face!  Penicillus are found in seagrass beds and sand flats where one also finds Halimeda.  Like Halimeda, Penicillus also has a holdfast to anchor it to the sand.  It can reach about 10 cm in height and is lightly calcified which acts to stiffen the plant so that it remains upright.  Calcification also helps to prevent grazing since it makes the plant harder to digest.  It does need to bend though because a strong current would uproot it from the bottom!