They are classified primarily into centric and pennate groups, then further by whether they possess a seam known as a raphe. They usually reproduce asexually in a unique "shrinking division" pattern that diminishes their size to a critical point, at which time growth occurs 
They are classified primarily into centric and pennate groups, then further by whether they possess a seam known as a raphe. They usually reproduce asexually in a unique "shrinking division" pattern that diminishes their size to a critical point, at which time growth occurs in the form of an auxospore, and earth rich in these organisms is mined commercially for its filtration applications. Their two-valved cell walls are known as tests, or frustules, and are made of a form of silicon. For 10 points, name these unicellular organisms, a type of Eukaryotic algae.
They are classified primarily into centric and pennate groups, then further by whether they possess a seam known as a raphe.