The subclass Copepoda is represented in the marine plankton by free forms belonging to eight out of the nine orders of this group of Crustacea (Boxshall & Halsey, 2004): Platycopioida, Calanoida, Mormonilloida, Misophrioida, Hapacticoida, Cyclopoida, Siphonostomatoida, Monstrilloida. Add Poecilostomatoida which can no longer be considered as a group phylogenetically separated from Cyclopoida, and the controversial Thaumatopsylloida which are rejected by the above mentioned taxonomists. The order of Gelyelloida is defined from species in subterranean karstic systems.
In spite of the vastness of the volume of the seas and oceans, the number of free marine planktonic species of Copepoda is relatively modest (approximately 2500 forms known to date) compared with that of the parasitic or benthic forms. The total number of species of Copepoda, free and parasitic, is probably underestimated with about 11500 (Bowman & Abele, 1982, Humes, 1994). The number of individuals is virtually incalculable; it constitutes the greatest part of the metazoans of our planet (perhaps except the nematodes).
The role of the free Copepoda in the pelagic ecosystem is essential from a trophic point of view, as a link between the primary production and the larvae and juveniles of fishes and perhaps cephalopods. They characterize the secondary production of the sea. The specific composition and the biological cycles of the species are essential factors to determine in the course of time. The species form important indicators for the different water masses, being directly related to the characteristics and dynamics of these.
The majority of the marine environment has been sampled, however unequally if one refers to the oceanic provinces, as well as in the bathyal and abyssal regions of the oceans and the underwater caves.
The aim of this work is to offer a synthesis of our current knowledge on the diversity of the forms and their geographical distribution, to define greater biogeographic entities, and to look for the mechanisms of dispersion or isolation.
This database has the ambition to be useful, in fine, for an overall treatment in order to define great biogeographic entities and to seek the mechanisms of dispersion or insulation.
Sewell (1948, 1956) showed the way to be followed in the interpretation of the geographical observations of the species. The marine planktonic organisms depend primarily on the major oceanic surface and deep currents, as well as on their preferential bathymetric localities (Murray & Hjort, 1912; Raymont, 1983), with their more or less important capacity for circadian and/or ontogenetic migrations adding further complication.
Age of the group, which is presumably post-Precambrian (Sharov, 1966; Boxshall, 1983, Huys & Boxshall, 1991), and our ignorance about the evolution of the Copepoda and of the chronology of appearance of the genera (for lack of fossils), impede any interpretation in relation to the continental drift.
More recently Van der Spoel & Heyman (1983), by taking into account various zooplanktonic forms, redefined large biogeographic provinces.
The ecophysiology of the species is generally insufficiently known or not very exploitable to understand their localities. On the other hand Brodsky & al, 1972 (in Zvereva, 1972, editor) showed the importance of the functional ecomorphology to explain, for example, the geographical distribution of Calanidae.
One of the difficulties encountered in trying to draw up the cartography of the species comes from often too incomplete or insufficiently illustrated species descriptions, sometimes involving complex synonymies. A literature difficult to pull together and the absence of a world fauna, which should take into account the natural dispersion of the pelagic species, increase the difficulties of identification. This last problem has been considerably improved thanks to the publications from Bradford-Grieve (1994, 1999) and Boxshall & Halsey (2004) (see faunas preceded by * at the end of the chapter).
The study of structural variability and the biometric approach of the species within the populations are rarely considered (Brodsky, 1965; Frost & Fleminger, 1968).
The study of the epicuticular structures developed by Fleminger (1973), Vaupel Klein (1982), Mauchline (1988), or those of the isoenzymes or ARNm (Sévigny & Al, 1989; Cervelli & Al, 1995; Bucklin & Marcus, 1985; Bucklin & Al, 1989, 1995, 1996; Bucklin & Kocher, 1996; Kann & Wishner, 1996), can only be associated with a macroscopic initial identification.
Many systematic inventories, resulting from ecological works, are sometimes of doubtful value, whatever the sophisticated mathematical treatment, associated with them. To realise this it is sufficient to consult the bibliographical references, very few of which mention faunas or morphological documents used, and the respective sex of the animals is generally not specified. Moreover the practice of subsampling for countings overemphasizes the most abundant species at the expense of the rarer forms which are interesting from a geographical point of view.
Finally the type of mesh-size of the nets, like the sampling method, introduce considerable bias. More significant is undoubtedly the "moment" of sampling compared to the biological cycle of the species.
In addition to the test of synthesis of Sewell, we point out the geographical localities and the frequency of the pelagic species of the Copepoda, thanks to various marine records of importance, in the form of "regional" faunas ( * in Références ),
of more or less extended zones, like the North Atlantic and the North Sea prospected during many years using the "Continuous Plankton Recorder" (Colebrook, 1975), or geographical points related to the presence of marine laboratories, some of which are more than one hundred twenty years old, and more exceptionally of fixed stations off shore ( see List of the studied authors ).
A general and biogeographic systematic inventory can, to a certain extent, provide useful indications at the time of the identifications, or at least draw attention to the species.
Let us underline the particular cases of endemism observed in geographical places that are sometimes extremely distant and the role of anthropogenic transport (Carlton & Geller, 1993).
This inventory treats all the species listed starting from the work of Giesbrecht (1892 [actually "1893"], after Holthuis & Vervoort, 2006) up to 2019.
It is based on the analysis of more than six thousand publications, either of a purely systematic nature, or dealing with ecology. It cannot be regarded as exhaustive, nor safe from errors or lapses of memory, but the consulted publications correspond to a world "sampling" ( the authors and the prospected zones are quoted in the appendix : List of the studied authors ).
In the case of certain species the critical analysis starting from the literature does not make it possible to be sure about their validity or their synonymy; these cases are indicated in the remarks for each one of them.
Faunas and References