Pelagic species are widely distributed in a horizontal plane and have three-dimensional distributions, since the sea covers about 70% of the surface of the earth, and on average 4 km deep. For most macrozooplankton and micronekton groups there seems to be no great expectations of finding new taxa with the exception of gelatinous groups and of the deep sea, which is a relatively unknown especially in the benthopelagic zone close to the sea-bed. However, we do not know very much about variation, either morphological or genetical, within socalled species in different parts of their range. We think we are dealing with single very broadly distributed species, which, in reality, are species complexes consisting of several more or less cryptic species or infraspecific categories. Examples are given in different animal phyla of the same phenomena e.g. that we find variation in consistent geographic patterns. The recognition of the true dimensions of the species diversity and variation in the ocean may give us a new view about the so-called speciespoor pelagic system. Much more research is needed before we can have real confidence in our estimates of the numbers of species existing in the pelagic realm.

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Zoologische Verhandelingen

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Naturalis journals & series

Pierrot-Bults, A. C., & van der Spoel, S. (2003). Macrozooplankton diversity: how much do we really know?. Zoologische Verhandelingen, 345, 297–312.