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Specimen
082
Pinnularia is a predominantly fresh-water algae.Pinnularia are elongated elliptical unicellular organisms. Their cell walls are composed chiefly of pectic substances on a rigid silica framework. Their walls are composed of two halves called thecae (or less formally, valves.) These halves overlap like a Petri dish and its cover. The margins of the two thecae are covered by a connecting band called a cingulum and all together are referred to as a frustule. The cytoplasm is arranged approximately in layers conforming to the shape of the cell's walls. A large central vacuole is present with the nucleus suspended in its centre by a transverse cytoplasmic bridge. Two chloroplasts are present along the sides of the cells, and contain chlorophyll a, c, beta-carotene and fucoxanthin pigments. One or two pyrenoids are usually present in each chloroplast, although like many heterokont algae Pinnularia tend to store their energy as fat. The cytoplasm also contains chrysolaminarin and some volutin. Locomotory organs are absent in Pinnularia - it moves by characteristic gliding movements. Circulation of the streaming cytoplasm within the raphe causes this movement. |