The majority of harpacticoids show a great dependence on the peculiarities of their habitat. This research attempted to detect the possible existence of biogeographical and ecological trends. The limited biogeographical data is discussed, so this is applied the method of analysis of morpho-ecological correlation (Jakobi, 1962) developed to determine ecological trends. This way, all characteristics of the harpacticoidean body selected were studied to check their adaptative value. Based on those results it was possible to establish and to define ecological units. Data were then subjected to statistical tests of homogeneity for variance and significance. Graphs are used to demonstrate the natural adaptation process. Diagrams permit one to recognize the general tendencies as well as degrees of specific evolution. Nevertheless, quite different principles such as type formation and atomic orbit model analogy, were applied to understand biogeographic trends. The change of the endopodits of the 4th leg of adult males (Enp. P4 male) is utilized as an example.