A Protists with purely plant-like nutrition (photosynthesis): DIATOMACEA (Cretaceous to Present)
Diatoms have brown protoplasm enclosed in a rigid silica skeleton. They occur as plankton and benthos in marine and fresh water. They are important primary producers of the marine food chain.
B Protists with characters intermediate between animals and plants; some are capable of swallowing solids, but most depend on photosynthesis; capable of locomotion by means of flagella:
COCCOLITHOPHORIDA (Jurassic to Present) Organisms with the envelope of the cell covered by calcareous discs (2 to 30 microns in diameter). Coccoliths are pelagic; marine or fresh water.
SILICOFLAGELLATA (Cretaceous to Present)
Organisms with a skeleton composed of hollow bars of silica.
DINOFLAGELLATA (Silurian to Present)
A varied group of organisms, many of which have cellulose plates (6 to 100 microns); some may be the origin of acritarchs (which are known from the late Precambrian and later systems).
The Zooxanthella may be related; they are round yellow-green cells which live associated with hermatypic corals and some other marine invertebrates.
C Protists with purely animal-like nutrition (including the Protozoa); mostly feeding on organic matter; no photosynthesis. Most soft-bodied, but one phylum includes animals with hard parts.
PHYLUM SARCODINA (Cambrian to Present) class ACTINOPODA (Cambrian to Present)
subclass RADIOLARIA (Cambrian to Present)
Marine pelagic protozoans with hard parts of silica or strontium sulphate. As silica does not dissolve as readily as calcite in very deep water, radiolarian deposits are commoner in very deep water sediments.
class RHIZOPODEA (Cambrian to Present)
order Foraminiferida (Cambrian to Present)
Protoplasm of body supported by a skeleton usually calcareous. Mostly in marine or brackish water. Mostly benthic, but some pelagic; pelagic foraminifera (e.g. Globigcrina) are important in Cretaceous and Tertiary stratigraphy.
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