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.