The total number of marine and brackish planktonic species of copepods is evaluated at about 1950, belonging to 9 of the 10 sub-classes of Copepoda. Only the Gellelyoida, which are fresh-water and underground forms are not considered. These species are distributed over 59 families and 253 genera. According to the genera number distribution in families, 2 families yield the largest generic radiation: the Aetideidae and the Scolecitrichidae, with a dominance of mesopelagic and bathypelagic species. 63% of families have a restricted number of genera (1 to 3), some belonging to orders having their full expansion in the benthos. The families with epipelagic forms and those with herbivorous and omnivorous characters are weakly diversified in contrast to carnivorous forms. Sex-ratio analyses based on the number of individuals in samples indicate a strong dominance of females; one has to take into account, however, that both males and females are described for 67% of the total number of species, 28% is exclusively based on females and 5% on males.
