Actinoptychus sp., a solitary centric diatom commonly found in coastal marine plankton samples.
Diatoms (the Bacillariophyceae) are some of the most beautiful organisms to look at under a scope! Their cell walls are shaped like tiny glass pill boxes, with an amazing array of sizes, shapes and ornamentation (see the diatom photo gallery). You can find diatoms drifting in the plankton or you can find them gliding along the benthos in just about any marine habitat. They are non-motile - the only flagellated stages are sperm, found in some species - so often planktonic diatoms will have elaborate ornamentation to help them stay aloft in the water and closer to the sunlight. There are two basic body shapes, centric (round, Order Centrales) and pennate (thin ellipse, Order Pennales), and either may be found in the plankton or on the benthos. While the pennate diatoms are solitary cells (although often living in dense assemblages or even forming tubes together), the centric diatoms may be solitary (as shown in the picture above) or chain-forming, linked by projections from their cell wall or membrane. When nutrient and light conditions are right, all diatoms are able to bloom - reproduce very quickly into huge numbers. They do this through vegetative or asexual reproduction.
Previous participants of the botany class have worked on diatoms, so use the following links to learn more:
Cell size: 20-200 m m
Cell wall: SiO 2 or glass frustule
Chloroplasts: many/cell, 3-5 thylakoid membranes/stack
Photo-pigments: chlorophyll a & c, carotenoids
Reproduction: most often simple cell division, sexual reproduction
Ecological roles: produce deposits (diatomaceous earth), toxic blooms
© 2001 Caren E. Braby