cyanobacteria are among the genera Hemiaulus, Rhizosolenia and Chaetoceros. Dinotoms are diatoms that have become endosymbionts inside dinoflagellates. Research on the dinoflagellates Durinskia baltica and Glenodinium foliaceum have shown that the endosymbiont event happened so recently, evolutionarily speaking, that their organelles and genome are still intact with minimum to no gene loss. The main difference between these and free living diatoms is that they have lost their cell wall of silica, making them the only known shell-less diatoms. The study of diatoms is a branch of phycology. Diatoms are classified as eukaryotes, organisms with a nuclear envelope-bound cell nucleus, that separates them from the prokaryotes archaea and bacteria. Diatoms are a type of plankton called phytoplankton, the most common of the plankton types. Diatoms also grow attached to benthic substrates, floating debris, and on macrophytes. They comprise an integral component of the periphyton community. Another classification divides plankton into eight types based on size: in this scheme, diatoms are classed as microalgae. Several systems for classifying the individual diatom species exist. Fossil evidence suggests that diatoms originated during or before the early Jurassic period, which was about 150 to 200 million years ago. The oldest fossil evidence for diatoms is a specimen of extant genus Hemiaulus in Late Jurassic aged amber from Thailand. Diatoms are used to monitor past and present environmental conditions, and are commonly used in studies of water quality. Diatomaceous earth (diatomite) is a collection of diatom shells found in the earth's crust. They are soft, silica-containing sedimentary rocks which are easily crumbled into a fine powder and typically have a particle size of 10 to 200 μm. Diatomaceous earth is used for a variety of purposes including for water filtration, as a mild abrasive, in cat litter, and as a dynamite stabilizer. Overview Diatoms are protists that form massive annual spring and fall blooms in aquatic environments and are estimated to be responsible for about half of photosynthesis in the global oceans. This predictable annual bloom dynamic fuels higher trophic levels and initiates delivery of carbon into the deep ocean biome. Diatoms have complex life history strategies that are presumed to have contributed to their rapid genetic diversification into ~200,000 species that are distributed between the two major diatom groups: centrics and pennates. Morphology Diatoms are generally 2 to 200 micrometers in size, with a few larger species. Their yellowish-brown chloroplasts, the site of photosynthesis, are