Giant Acorn Barnacle (Balanus nubilis)

A Giant Acorn Barnacle at the Pacific Northwest intertidal. (Balanus nubilis) Incredibly, giant acorn barnacles possess some of the largest muscle fibers known to science, a fact that makes them ideal (and often-studied) subjects in investigations of muscular tissue. These muscle fibers, known as myocytes, are actually some of the largest cells in the animal kingdom—an individual myocyte from B. nubilis can measure two millimeters or more in diameter, about 25 times thicker than the average human hair. By contrast, myocytes found in the human heart have a diameter of 0.015-0.020 millimeters—almost 100 times thinner than the largest B. nubilis muscle fibers.