Genetic relationship between pelagic and benthal organisms
Abstract
Having to choose between two alternatives, the primariness of benthal or of pelagic organisms, the author prefers the first, adding some new arguments to the listed old ones in favour of his opinion. The author’s propositions that Eumetazoa have not developed from protozoa colonies but from infusoria with several nuclei, and that the relationship between ontogeny and phylogeny as formulated by H a e c k e l are incorrect, facilitate the argumentation in favour of the primariness of benthos. Since the specific gravity of protoplasms, from the very beginning, has exceeded that of sea water, the transition from benthos to plankton required special adaptions. The very composition of plankton as we know it at present indicates that its development must have taken place at the expense of benthos. There is no higher organic form among plankton organisms that cannot be found among benthal organisms. Benthos, on the contrary, contains a variety of higher forms either not occurring among plankton organisms at all or found only among some plankton species and representing, more than probably, later additions. The purely planktonic groups, coming from benthal groups, have either gone through a neoteinic evolution or it can be supposed, with a considerable amount of certainly, that some bethal groups have subsequently joined plankton retaining their original forms.
The development of pelagic organisms can be divided into three stages. The first to appear were minute autotrophic protophyta from the bottom layer actively motile by means of unudulating flagella. Heterotrophic protista, protozoa, came after them. In the course of the second stage, when eumetazoa developed on the sea bottom, their free ontogenetic forms, i. e. their larvae, joined plankton as microphage, but returning, as a rule, to the bottom as soon as their metamorphosis was completed.
Attracted by the abundance of minute phytoplankton, even some adult metazoe (crustaceans) joined plankton and the larvae of some benthos species discontinued to return to the bottom. Plankton itself went trough the process of natural development and differentiation becoming what is known as nanoplankton, microplankton, and macroplankton. The condition were thus created for pelagic organisms to reach the third stage of their development and for the appearance of nekton, partly preying upon smaller nekton.
It can be stated, in conclusion, that the early development of pelagic organisms was at the expense of shallow-water benthos. This is equally true of the deep-sea fauna, of the freshwater one, and even of the land fauna. The further development of pelagic organisms paralleled that of benthal ones, new elements having been added to the former, among which some of the new elements grew into specialized plankton species while others rejoined the benthal species. Nekton was the last to appear. Plankton, representing the source of nourishment even for benthal organisms, thus grew in importance. Benthos with bacteria, in return, became important for the sustenance of plankton, renewing the supply of salts required by the metabolic process and used up so quickly by the lush growth of plankton.
