Typically elongated, straight, and slender, these organisms may also have an ovoid or slightly sigmoid shape. They’re often found individually but can aggregate to form star-shaped colonies or reside within mucilage tubes. Usually, each cell contains two plastids positioned toward the poles of the cell. The raphe system, which is fibula-shaped, is typically situated on or close to the valve’s edge. In the frustule, the raphe exists on opposing margins of the two valves. These organisms undergo cycles of both asexual and sexual reproduction in alternating phases.