Silicoflagellates

Two silicoflagellate skeletons. Distephanus crux (left) is a common silicoflagellate from the Oligocene and Miocene Epochs; Distephanus speculum (right) is common in the late Miocene to Recent. Both specimens are from the Weddell Sea near Antarctica (see McCartney and Wise, 1990)



The silicoflagellates are single-celled plankton that have a delicate siliceous skeleton made up of tubular rod-shaped elements. The silicoflagellates are a group of algae of the Order Dictyochales, which is now generally considered to be in the Division Chrysophyta, or golden algae, on the basis of pigmentation and the structure of the chloroplasts and mitochondria.

Silicoflagellates first appear in the Lower Cretaceous, are abundant and diverse in the Upper Cretaceous, and have an extensive record throughout the Cenozoic. The group is exclusively marine and in life is generally restricted to the euphotic zone. At death their skeletons settle to the ocean bottom, where they generally make up 1 - 3 % of the siliceous component of deep-sea sediment. Silicoflagellates tend to be abundant where diatoms are also common; the skeletons of both groups are of similar size, composition, and geologic range and are thus commonly found together. Like the diatoms, the silicoflagellates are especially abundant in areas of upwelling and in equatorial waters but are also abundant at high latitudes.

Silicoflagellates are fairly good biostratigraphic indicators, especially at higher latitudes and in deeper waters where calcareous microfossils are less common or dissolved. Silicoflagellate biostratigraphic zonations are available for high, middle, and low latitudes through most of the Cenozoic, but the zones generally cover longer intervals than are typical for foraminifera, coccoliths or diatoms. Their biostratigraphic use is somewhat complicated by a remarkable skeletal variability, and the group appears to be easily influenced by environmental changes.

The silicoflagellates can be considered the least important of the major microfossil groups. They deserve some time in the microfossil component of a paleontology course, but not the same amount given to more abundant and diverse groups such as the diatoms and radiolarians. However, students can expect to find silicoflagellates in microscope slides prepared for diatoms, and they may be struck by the beauty and simplicity of the silicoflagellate skeleton. This skeletal simplicity can also be useful in presenting the range of variation of some microorganism taxa.

from McCartney (1995)
(see publications list for references)

See a silicoflagellate publication on pdf format

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