Oithona similis

Taxon-Order: 
Cyclopoida

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Distribution: 
Known from all ocean basins. Within the Pacific: Subarctic, California Current, eastern equatorial Pacific, Subantarctic.
Habitat: 
Epipelagic to mesopelagic.
Size: 
Females 0.7-1.0 mm; Males 0.6-0.7 mm Total Length
Diet: 
Carnivorous, feeding on motile phytoplankton and microzooplankton.
Predators: 
Predatory zooplankton, fish.
Useful Facts or Characters: 

Rostrum not visible in dorsal view, but the small hook-like rostrum is visible in lateral view.

Natural History: 

A 'sit and wait' hunter, they provide few clues (either hydrodynamic or visual) to their presence. In the North Sea O. similis has been shown to have very low mortality rates (Eiane and Ohman 2004), which helps explain why they are so abundant in the ocean.

References: 

http://www.marinespecies.org/copepoda/aphia.php?p=taxdetails&id=106656

http://copepodes.obs-banyuls.fr/en/fichesp.php?sp=1803

http://www.arcodiv.org/watercolumn/copepod/Oithona_similis.html

Eiane, K., and Ohman, M.D. (2004) Stage specific mortality of Calanus finmarchicus, Pseudocalanus elongatus and Oithona similis on Fladen Ground, North Sea, during a spring bloom. Marine Ecology Progress Series 268: 183-193.

Nishida, S. (1985) Taxonomy and distribution of the family Oithonidae (Copepoda, Cyclopoida) in the Pacific and Indian Oceans. Bulletin of the Ocean Research Institute of the University of Tokyo 20: 1-167.