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Tintinnids are ciliates of the marine taxon Tintinnida, recognized for their formation of vase-shaped coverings called loricae, which may incorporate minute pieces of rock. Although appearing as early as the Ordovician period, tintinnids became abundant in the fossil record during the Jurassic. Tintinnids are an important part of the fossil record because of the rarity with which most other ciliates become preserved under the conditions of the marine environment. The loricae of tintinnids are easily preserved, giving them an extensive fossil record.
Tintinnids feed primarily on photosynthetic algae and bacteria. They are part of the microzooplankton: animals (as opposed to plants) between 20 and 200 micrometres in size. Tintinnids are found in salt and freshwater. They are most common in salt water and are usually present in concentrations of about 100 a liter but can reach abundances of several thousand per litre. Characteristics of their lorica, or shells, are used to distinguish between the roughly 500 species described. Like other members of the microzooplankton, tintinnids are a vital link in aquatic food chains as they are the 'herbivores' of the plankton. They feed on phytoplankton (plant plankton) and in turn act as food for larger organisms such as small crustaceans and larval fish.