Plankton Nets are a modification on the standard trawl used to collect planktonic organisms, of nearly any size, intact. Towed by a research vessel, Plankton Nets have a long funnel shape that allows them to catch differently sized plankton simply by changing the mesh size of the net. At the end of the funnel is a collection cylinder called a cod-end.
A ring net, a common form of Plankton Net, being readied for use during Arctic shelf research. (C.A. Linder, Wood's Hole Oceanographic Institute)
Bongo nets , such as these pictured here on the NOAA ship McARTHUR, are another common design. (NOAA Ocean Explorer)
The multinet,  a vertically profiling Plankton Net used to collect depth-stratified samples of small zooplankton such as copepods. (Mid-Atlantic Ridge Ecosystems - MAR-ECO. Filipe Porteiro)
This amphipod trap is specially designed to collect intact specimens of zooplankton and small crustaceans such as amphipods. (Census of the Diversity of Abyssal Marine Life - CeDAMar)