Anchialine caves are tidal, subterranean, inland habitats with a salinity-stratified water column and exchange of saltwater with the sea. They primarily occur on oceanic islands and some peninsulas with karstic limestone or volcanic terrain and include some of the longest explored caves on Earth. Use of specialized scientific cave-diving technology is essential to access this environment. A diverse, specially adapted fauna, dominated by crustaceans and other invertebrates, inhabit deeper, euhaline waters in anchialine caves. A number of new higher taxa, e.g., class Remipedia and order Mictacea, exclusively occur in this habitat. Some groups of anchialine fauna are found on opposite sides of oceans or even opposite sides of the Earth, and others have close relatives in the deep sea. Chemoautotrophically based food webs have been identified providing food in the otherwise lightless and nutrient-limited cave environment. Investigations of anchialine caves and their fauna by diving are a recent development so that much work remains. Only a small percentage of anchialine caves have been explored, much less scientifically studied, suggesting many new discoveries still wait.
