The remarkable diversity of subterranean Cirolanidae (Crustacea: Isopoda) in the peri-Caribbean and Mexican Realm

With 42 endemic species (one of them with two subspecies) described to this day, most of them belonging to 11 endemic genera, the peri-Caribbean – Mexican zone has definitely the richest fauna of stygobitic (entirely subterranean-adapted) cirolanids of the world. After a succinct presentation of the various habitats for stygobitic cirolanids in the zone, the species are grouped together (Table 1) according to their affiliation to habitats of freshwater or of marine water – water salinity being considered the most reliable common denominator. A check-list in alphabetical order follows, including references, known distribution, information on habitats, etc. That this is a case of very high biodiversity of stygobitic Cirolanidae results from comparison with the situation in the rest of the world. Some aspects of morphology in relation to systematics are reviewed (i.a.: evolutive significance of some morphological adaptations; monophyly of stygobitic genera). Attempts are made to reply to questions like: what can we know about ancestors of stygobitic species? Can age of stygobitic taxa, or lineages, be appreciated with some degree of reliability? What can we guess about the roots of present-day diversity (two types of habitat requiring different explanation for time and mode of groundwater colonization being recognized)? How deep are these roots? What is the legacy of Tethys? This case of high biodiversity could be explained through the rich, turbulent history of this vast and fragmented area; through the abundance and extraordinary diversity of habitats propitious for stygoevolution; and through the (supposed) abundance and high diversity of potential marine ancestors. A final part of the paper is devoted to endangered or already destroyed habitats and fauna, with a plea for protection.