Taxonomy and biodiversity of calanoid copepods

The sea-floor habitat is populated by many small calanoid copepods, which are an extremely abundant and diverse group of organisms and contribute up to 90-97% of the total biomass of the animals living in the World Ocean. Their fauna remains very poorly-known due to the technical difficulties associated with sampling in the habitat close to the near-bottom, especially at abyssal depths. 

A new stage in the research of the biodiversity of benthopelagic calanoids has been started in the end of 20th century and has been determined by the invention and use of modern devices for the sampling in the vicinity of the sea bed. Major part of these calanoid taxa have never been found outside the near bottom. These new data on the benthopelagic calanoids showed that the near-bottom is inhabited by calanoids with specific morphological characters (e.g. sensory setae) differing from those of their pelagic relatives. For the benthopleagic taxa heterobathmy (combination of plesiomorphic and apomorphic features) appeared to be typical. As the system of the order Calanoida was established at the edge of the 19-20th centuries, when these taxa were not known, an update by modern data is inevitable and it is now necessary to revise many families, and especially their near bottom representatives.

Collections obtained my modern devices like Epibenthic sledges recently used in the German expeditions on board of R/V “Polarstern” and “Meteor” or samples collected by the USA submersible “Alvin” are unique in the fact that they contain high numbers of new and rare taxa, and show that the biodiversity of the near-bottom biotop is very high. In the recent decade more than one third of all known benthopelagic genera were described.

Among the benthopelagic taxa, clausocalanoidean copepods are the most numerous calanoids in the near-bottom biotope. The diversity of taxa in this superfamily is very high and includes 94 genera in 11 families, of which 46 genera are exclusively benthopelagic constituting about 63% of the near-bottom calanoid copepod genera. As they are a link between benthic and pelagic ecosystems, Clausocalanoidea are extremely interesting from a taxonomical as well as from an ecological point of view.