A. palmata is an arborescent bryozoan whose colonies form limp, tufted tangles that are brown in color. Zooids occur only at the tips of branches and do not bud from the sides of mature individuals as occurs in other species. Individual zooids are cylindrical and measure approximately 0.79 X 0.13 mm (Winston 1982). The lophophore measures an average of 0.205 mm in diameter, and bears 10 tentacles. Colonies tend to become covered in a fine layer of silt that makes them opaque in appearance.