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The Prymnesiophyceae
are characterized partly by sub-light-microscopic features, including
plastids surrounded by four layers of membrane indicating a history of
successive “packaging” by endocytosis. Thylakoids are stacked in triplets,
chlorophyll is both a
and c,
and the storage reserve is chrysolaminarin. Other
classes (Eustigmatophyceae, Raphidiophyceae,
and Tribophyceae) share all these features. The name "Prymnesiophyceae"
was established by Hibberd (1976) to satisfy the International Code of
Botanical Nomenclature by using the root of a genus (with the use of Prymnesium
in this case). The previous name "Haptophyceae"
(Christensen 1962) was based on the presence of an appendage unique to this
protistan class, located between the flagella that superficially resembles
them, the haptonema
that has no homologue outside the class. Various species have differing
lengths and flexibilities of haptonemas, and their function also varies from
grasping objects to none observed. Most species are marine (~300), fewer than 10 are in
freshwater. Freshwater habitats include lakes with low conductance. Blooms of
Chrysochromulina
have occurred after loading of organic solutes
(human sewage) in a New Hampshire lake (personal observation). Some
genera including the coccolithophores and Phaeocystis are strictly marine
plankters. One of these, Emiliani, is the main source
of lime (CaCO3) in chalk cliffs as found in England and Germany. |
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References: |
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Christensen, T. 1962. Alger, in: Böcher, T.W., Lange, M., Sørensen,
T., Eds., Botanik, Vol. 2. Systematisk
botanic. Munksgaard, Copenhagen (178 p.). Hibberd, D.J. 1976. The ultrastructure and taxonomy of
the Chrysophyceae and Prymnesiophyceae (Prymnesiophyceae): A survey with some new observations on
the ultrastructure of the Chrysophyceae. Bot. J. Linnean Soc. 72:55-80. |
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