Abstract | Introduction | Presentation | Diversity | Main marine currents | The different oceanic zones : Summary of the species - Marine currents and other maps | Cosmopolitanism and endemism |
Species indicative of continental drift | Species whose localization is difficult to explain | Anthropic mechanisms | Conclusion
The total number of forms recorded since the work of Giesbrecht (1892) is 2644 (named and indetermined forms). Excluding Saphirella and Tisbe, 2510 (named), with the clear domination of 1986 Calanoida (79.1 %), the principal order of pelagic copepods, and 524 to the other orders (20.9 %) Given the immensity of the available volume, this very low diversification in the strictly planktonic forms reflects the difficulties surrounding speciation in such a medium.
The sex-ratio is 1 for 1542 species (i.e. 63.5 % of all the recorded forms, excluding Saphirella); 734 forms were described from females alone (i.e. 26.5 %) and 173 from males (i.e.
5.9 %). The apparent imbalance in favour of females in the catches results from biological bias (longer lifespan for females than for males) and/or for chorological reasons (different vertical distributions).
The average percentage of species per geographical zone is of
17.5 % (i.e.
464 ± 194 species). The lowest percentages are found in the Arctic and Antarctic stricto sensu, and in those regions where the frequency of observations is lowest: South and Southwest Atlantic, Red Sea, Southeast Pacific, China Seas. The highest values come from the Indo-Pacific region.
Cosmopolitan species represent only 24 percent of all forms recorded, reflecting not only the relatively restricted extension of the various populations, but also the shortage of analyses of the very little-explored deep-sea biotopes.
The distribution of many species may be linked to continental drift since the Cretaceous and more recently to glaciation, and also to the great main currents, but it is never easy to identify the determinant factor.
Certain localisations seem anthropic in origin, others remain unexplained - for some, the validity of the relevant observations has been demonstrated, but for others, erroneous identification remains a possibility untill the validity of observations shall be confirmed by methods which should be different than morphology.