It is a well-known faet, that both the geographie distribution and the speeiation of plankton are produets of the geologieal history of the oeeans, the eontinental barriers, the eurrent patterns and the limitation of survival of individual speeies and populations by both biotie and abiotie environmental eonditions. The geographie distribution is also the produet of the mobility of populations, the seleetive pressure and the time during whieh a taxon has existed. A taxon eonsists of a population, or a group of populations, suffieiently distinet to be provided with a name, to be ranked in a...