A synopsis of the milliped genus Abacion Rafinesque (Callipodida: Caspiopetalidae)

The milliped genus Abacion is summarized, and tesselatum Rafinesque, lactarium (Say), magnum (Loomis), and texense (Loomis) are recognized as valid species even though a low level of gene interchange may be occurring between tesselatum and magnum in coastal Georgia and tesselatum and lactarium in Illinois. Geographic races do not appear to be developing in any species, and all other species group names are relegated to appropriate synonymies. Abacion occurs widely in the eastern half of the United States, from the Atlantic Ocean to the central Great Plains and from the Great Lakes to southern Florida and northeastern Mexico. Species ranges overlap broadly, and instances of sympatry and syntopy are common. The species are similar anatomically, and the most reliable taxonomic characters are found on the male gonopods, particularly the configurations of the coxal processes and the distal elements of the telopodites.