(well, if you look at the fish part of this very website)
Algae Blenny
or Salarias fasciatus
Taken from another website
Notes: An excellent housekeeper for your reef aquarium this Blenny will eat a wide variety of hair and string algae. Sometimes called by other names Lawnmower suits this fish best. A common sight is of this fish with a fat belly perching on a clean rock after its meal. Make sure to provide live rock for it to graze on and perch on. Although the microalgae that grows in your aquarium may provide enough food you may supplement its diet with herbivore preparations of marine and spirulina algae.
Usually not aggressive towards other fishes, with the possible exception of similar blennies such as the Black Sailfin Blenny and Horseface Blenny.