Monterey Bay Aquarium Research Institute
Marine Botany

Diatoms Pennales

Pennate diatoms, or pennales, may be long or pen-shaped, or may be broadened in the middle until almost round. Unlike Centrales, they have bilateral symmetry; their shell, or test, is composed of two mirror-image halves. They will typically have a raphe, or groove usually lined with cilia, down one side.

Pennate forms are most common in fresh water or living on the bottom or other substrates in the ocean. The ciliated raphe helps them glide along these surfaces. In a plankton tow performed off Cabrillo Point in Monterey in winter, they were far less common than centric forms.

A few pennate diatoms are responsible for poisoning of humans. Pseudo-nitzschia and a few other species produce the toxin domoic acid. If a bloom of these species occurs, the diatom toxin accumulates in mussels, making them unsafe to eat. It has been suggested that an encounter with a domoic-acid crazed seagull was the inspiration for Alfred Hitchcock's The Birds.

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copyright John Becker 1996.

Last updated: Feb. 05, 2009