Attheya armatus

Attheya is also a diatom, but is found only in the surf zone of Washington coastal beaches. It looks a little like Chaetoceros, but the spines are different and are called horns. The cells are either solitary or attached to each other to form short chains of up to eight cells. Cells are frequently attached to sand grains. Attheya occurs mostly in the fall, winter, and early spring and is an important food source for clams living in the beaches. When cells are present in high numbers (blooms) they may turn the surf black and be mistaken for an oil slick.