The reciprocal influence between benthos and pelagos is inversely correlated with the distance between the water level where each species thrives and the sea bottom. The world ocean has an average water column of 3800 m; thus, we can easily imagine how true pelagos exist in the so-called open sea”, where marine environments with a water column deeper than 200 m represent the widest part of the planet’s surface (approximately 70%). Larvae and drifters exist in any part of the oceans, but most living organisms in the Pelagos have to belong to the Holoplankton and/or to the pelagic Nekton, with lifestyles and adaptations completely dictated by the absence of any solid surface that they can interact with. The richest part of this world is the epipelagos, a layer between the surface and − 200 m where the sunlight is still enough to allow photosynthetic production of biomass higher than its metabolic consumption. Immediately below this arbitrary limit is the twilight zone, between 200 and 1000 m of depth, where photosynthesis is still possible, but the metabolic consumption of organic matter is more important. The remaining part of the pelagos is below such a limit in complete absence of the sunlight and at constant temperature, salinity, and pH. The organisms of the largest planet domain, as a consequence, have to be mostly adapted to stay without any solid surface to touch, in constantly cold water conditions, and in the dark for their whole life duration. This lifestyle requires buoyancy strategies and/or swimming capacities to stay in the water medium. The ocean currents distribute plankton, and swimming allows organisms (the largest ones more than the smallest) to thrive in all the ocean partitions (horizontally and vertically), thus generating a biogeographic frame more complex than that derived by the common geographic approach, based on continent/ocean borders. The limits of the pelagos and partitioning inside this world are not those suggested by our necessity to put order in our knowledge, and organisms group together or separate from each other according to the existence of water mass borders. Contact areas (water–air, water–sediment, and between different water masses) are those where biomass and diversity are concentrated and justify the adoption of a specific terminology (neuston, hyperbenthos) to indicate typical communities.