Chromista is a eukaryotic kingdom of mostly aquatic organisms. The kingdom includes several important organisms such as diatoms, most algae, and some mildews. Most chromists are photosynthetic, and traditionally were classified as plants. Non-photosynthetic chromists were tossed into other kingdoms. Recent molecular studies (1980s) on the chromists led biologists to conclude that the photosynthetic chromists were very different from plants, and very similar to the non-photosynthetic chromists. A new taxon was born. Since the kingdom of Chromista is very new, it is known by other names--stramenopiles, heterokonta, and chromobionta. Most chromists contain carotenoid pigments such as fucoxanthin that give them characteristic colors and their name. Chromista means colored in Greek.
Photosynthetic chromists contain a unique chemical chlorophyll c which is not found in plants. Unlike plants, which store energy in starch, the chromists store energy in the oil leucosin and the polysaccharide laminarin. Typically the chloroplasts of the photosynthetic chromists are surrounded by the same membranes as the nuclei. Both the photosynthetic and non-photosynthetic chromists contain two flagella (though one might only be a stump). The longer of the two flagella is lined with hairs called mastigonemes. The Golgi apparati of many chromists produce silica or calcium carbonate skeletons that surround their cells. These skeletons are essential to their fossil record, which dates back to the precambrian. The skeletons of many chromists form extensive rock structures.
Chromists are ubiquitous in both fresh and marine water. Most are planktonic. However, kelp form huge forests on the ocean floor that are critical ecological structures. The Monterey Bay Aquarium, among others, has a kelp forest exhibit that extends over three floors. The photosynthetic chromists form the base of many aquatic food chains. Diatoms are important prey for small aquatic predators such as fish and jellyfish.
Chromista is currently a hot research topic among phylogeneticists. The classification of chromists is incomplete, and the evolutionary relationship between chromists and other eukaryotic organisms is unclear.
Phyla of kingdom Chromista
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