Morphology of the marine diatom Cocconeis pseudomarginata Gregory var. Intermedia Grunow

The morphology and fine valve structure of the marine attached diatom Cocco neis pseudomarginara Gregory var. intermedia Grunow was investigated. The e ntire frustule, internal and external structures of the raphid and araphid valves and complete cingulum are described using not only the light microsc ope and scanning and transmission electron microscope but also bleaching me thod and the focused ion beam technique. The raphe that terminates with a c omma-shaped helictoglossa internally is slightly sigmoid. The hymenes, with perforations arranged in a centric array, are located near the internal op enings of the areolae in the raphid valve (RV). The striae in the araphid v alve (AV) consist of alveoli occluded by hymenes that have perforations arr anged in a parallel array and locate near the outer surface. The complete c ingulum of AV consists of an afimbriate, open valvocopula and two bands wit h small ligula. The RV has only a valvocopula which is open type and not fi mbriate.