Characters of coloniality in diatoms

Developmental studies have revealed four types of structures that indicate colonial habit - spines, spinules, ridges, and granules. Spines link valves in colonies, as in Aulacoseira italica, and are of fairly constant shape. Spinules develop on the valve margins, and assist in linking cells, but their shapes and dimensions are variable, as in Diatoma hiemale. Ridges occur on the valve margins in pennate forms as low serrate siliceous outgrowths, e.g., in Didymosphenia geminata. Granules are produced on the contact surfaces in combination with other elements or alone. These types of contact structures correlate the longevity of the colonies. -Author