Dinoflagellate
Fossil dinoflagellates are important in stratigraphy, the dating and correlation of strata. During their life, dinoflagellates have a mobile planktonic form and a resistant cyst phase which enables them to survive over winter in sediment. Only the cyst gets fossilised. Their first certain appearance is in the Silurian period, with a big radiation in the Mesozoic era.p440 They are classified as Phylum Dinomastigota by Margulis and colleagues.