Order Calanoida Sars, 1903
The Calanoida is readily defined by the combination of the gymnoplean-type tagmosis, the presence of only one spine on the outer margin of the first exopodal segment of the second to fifth swimming legs, the presence of a coxal epipodite but not a lobate basal exite on the maxillule, and the presence of a seta on the inner margin of the coxa of the antenna. These are plesiomorphic characters, however, and it is difficult to identify apomorphies of the Calanoida. The presence of a maximum of 2 setae on the terminal (fourth) endopodal segment of the maxilla is an apomorphy of the Calanoida.
Calanoids are the planktonic copepods par excellence. They occur at all depths in the water column, from the surface to the abyssal trenches. Most are pelagic, living in the water column away from the influence of the sea bed. Some live in the near-bottom community and a few are more or less benthic. Calanoids are also abundant in the freshwater plankton and in inland saline habitats. They are typical members of specialized fauna of anchialine habitats. Many are specialist small particle feeders consuming the algal cells of the phytoplankton. Others are predators feeding on a wide variety of animal prey. All calanoids appear to be selective feeders and catch their food particles raptorially.
Huys and Boxshall, 1991