MicroscopicLife

They were first described by the Rev. John Harris in 1696, and other shapes were described by Antonie van Leeuwenhoek in 1703. Most rotifers are about 0.1–0.5 mm long (albeit their size can range from 50 µm to more than 2 mm), and are common in freshwater environments around the world with some saltwater species. Some rotifers are free-swimming and are truly planktonic, others move slowly along a substrate, and some are sessile, living inside gelatinous tubes or fixatives that are attached to a substrate. About 25 species are colonial (eg Sinantherina semibullata ), sessile or planktonic. Rotifers are an important part of freshwater zooplankton, being an important food source and with many species also contributing to the decomposition of soil organic matter. Most rotifer species are cosmopolitan, but there are also some endemic species such as Cephalodella vittata to Lake Baikal. Recent barcode evidence, however, suggests that some 'cosmopolitan' species, such as Brachionus plicatilis, B. calyciflorus, Lecane bulla, among others, are actually species complexes.

Gastrotrichs are microscopic multicellular organisms, so they are animals. They have many cells in their bodies. They show something called the eutely, meaning that the number of cells an individual has is based on its genome. For example, we have some trillions of cells in our bodies, and some of us have more cells, some have less, even though we are all Homo sapiens. . But gastrotrichs have a fixed number of cells for each species, if this one in the video has 1000 cells, each one of the trillions of others in the same species all over the world has 1000 cells!