Is the diversity of the Beach Flies adequately known? Some reflections on the state of the art of current knowledge (Diptera: Canacidae)

An overview of the major zoogeographical gaps in our knowledge of the world beach flies (subfamilies Apetaeninae, Horaismopterinae, Pelomyiinae, and Tethininae) is provided. The identified areas treated in this work are as follows: the subarctic Beringia, the South American circum-Antarctic islands, the Neotropical region south of the equator, most of the West African seacoasts, the huge area ranging from India, across the Bay of Bengal, to Sumatra and Java, and most of Australia. Apart from the inhospitable northernmost and southernmost areas of the planet, which feature a real very low biodiversity, the remaining vast areas dealt with in this work woefully suffer a dramatic paucity of field collections, as well as of previously collected materials preserved in scientific institutions. This might seem a truism that, however, must be emphasized in order to unequivocally identify the geographic areas that need to be further investigated. at the end of the discussion, the world distribution for all species mentioned in the work is also provided.