No clear distinction is made between "terrestrial", "semiterrestrial", and "aquatic" crabs. Rather, a continuum of terrestriality is displayed among the true crabs, although most land-adapted crabs must still return to water to release their
eggs. Some species of terrestrial crabs can be found many kilometres from the sea, but have to complete annual
migrations to the sea. Only a few land crabs, including certain
Geosesarma species, have direct development (the mother carries the eggs until they have become tiny, fully developed crabs), and these do not need access to water to breed. Many crabs belonging to the family
Potamidae, which contains mostly freshwater crabs, have developed a semiterrestrial (for instance the genus
Nanhaipotamon) to terrestrial life history, and are sometimes independent of fresh water for reproduction (for instance the genus
Tiwaripotamon). ==Ecology==