Darkield photomicrograph, diverse selection of diatoms, strewn selection, recent marine sample, Genoa, Italy
Diatoms belong to a large group called the heterokonts, including both autotrophs (, golden algae, kelp) and heterotrophs (, water moulds). Their yellowish-brown chloroplasts are typical of heterokonts, having four membranes and containing pigments such as the carotenoid fucoxanthin. Individuals usually lack flagella, but they are present in male gametes of the centric diatoms and have the usual heterokont structure, except they lack the hairs (mastigonemes) characteristic in other groups. Most diatoms are non-motile, as their relatively dense cell walls cause them to readily sink. Planktonic forms in open water usually rely on turbulent mixing of the upper layers by the wind to keep them suspended in sunlit surface waters. Some species actively regulate their buoyancy with intracellular lipids to counter sinking. A feature of diatoms is the urea cycle, which links them evolutionarily to animals. This was discovered in research carried out by Andrew Allen, Chris Bowler and colleagues. Their findings, published in 2011, that diatoms have a functioning urea cycle was highly significant, since prior to this the urea cycle was thought to have originated with the metazoans who appeared several hundreds of millions of years after the diatoms. Their study showed that while diatoms and animals use the urea cycle for different ends, they are seen to be evolutionally linked in such a way that animals and plants are not
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Photo credit: © Scenics & Science / Alamy / Afripics
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Keywords: biodiversity, darkield, diatoms, diverse, genoa, italy, marine, micrograph, microscope, photomicrograph, photosynthesis, phyto, plankton, sample, selection, strewn
