The factor of most importance to the structure of epipelagic oceanic c
ommunities is the absence of cover and the inability to hide from pred
ators in surface waters during the day (Elton, 1939). Visual predation
in an environment devoid of cover has resulted in convergent evolutio
n into only six modal adaptive patterns. Large, fast, visual predators
roam the water, 1) alone or in 2) schools, and they eat anything of a
ppropriate size that they see. Prey escape only by dint of 3) very sma
ll size, 4) invisibility due to tissue transparency, 5) diurnal vertic
al migration, or by 6) exploitation of the sea surface. The sensory ec
ology and physiology of zooplankton are different from that of all oth
er animal categories in all other habitats. Epipelagic zooplankton are
either extremely small animals, with small and structurally simple se
nse organs, or they are large, with gelatinous, transparent bodies whi
ch often lack sense organs.