Freshwater crab Freshwater crab There are around 1,300 species of freshwater crabs, distributed throughout the tropics and subtropics, divided among eight families. They show direct development and maternal care of a small number of offspring, in contrast to marine crabs which release thousands of planktonic larvae. This limits the dispersal abilities of freshwater crabs, so they tend to be endemic to small areas. As a result, a large proportion are threatened with extinction. There are more than 1,300 described species of freshwater crabs, out of a total of 6,700 species of crabs across all environments. The total number of species of freshwater
Paleontology and botany, as it deals with both living and fossil organisms. Micropaleontology deals with all microscopic fossil organisms, regardless of the group to which they belong. Instead of focusing on individual organisms, paleoecology examines the interactions between different organisms, such as their places in food chains, and the two-way interaction between organisms and their environment. One example is the development of oxygenic photosynthesis by bacteria, which hugely increased the productivity and diversity of ecosystems. This also caused the oxygenation of the atmosphere. Together, these were a prerequisite for the evolution of the most complex eukaryotic cells, from which all multicellular