Cyclopoid Copepod

Oithona similis

Only visible under a microscope. With the unaided eye, they will look like a little speck. They have an oblong body shape with long antennae and a long urosome (tail). Adults have enlarged genital segments. Adult females are generally larger than adult males. Adults are 0.6 to 1.2 millimetres in length.

Authority

Claus, 1866

Classification Details

Phylum: Arthropoda (arthropods); Subphylum: Crustacea (crustaceans); Subclass: Copepoda (copepods).

Habitat

Known from all ocean basins. On northwest Atlantic coasts from the Arctic to Cape Cod. Low salinity and low oxygen content can negatively impact their numbers.

Diet

Carnivorous. Prefer to eat motile prey such as ciliates, calanoid nauplii, and flagellates, but will also eat diatoms. They are hard for prey to see and adopt a sit-and-wait hunting strategy. Juveniles feed on dinoflagellates.

Reproduction

Sexes are separate. Physical and chemical cues assist in the pairing for mating. Males grab onto females and place a sperm packet to the female's genital region. It releases sperm to fertilize the female's eggs. Females carry eggs in egg sacs. The eggs hatch into nauplius larvae, which are very small. They have three pairs of appendages for swimming and eating. There are six nauplii molts, then five copepodite stages (which resemble the adult) before they molt into an adult. They live for approximately six months to a year.

Fun Facts

Oithona is among the smallest copepods. Their swimming motion is to alternate between slowly sinking and “jumping”. This movement is very energy efficient.

References

Castellani C (2005) Feeding and egg production of Oithona similis in the North Atlantic. Marine Ecology Progress Series 288, 173–182.

Hansen FC, Mollmann C, Schutz U and Hinrichsen HH (2004) Spatio-temporal distribution of Oithona similis in the Bornholm Basin (Central Baltic Sea). Journal of Plankton Research 26(6), 659–668.

Johnson WS & Allen DM (2005) Zooplankton of the Atlantic and Gulf Coasts. Maryland: Johns Hopkins University Press.

Scripps Institution of Oceanography. Oithona similis – Zooplankton Guide. https://scripps.ucsd.edu/zooplanktonguide/species/oithona-similis Accessed online 22 January 2020.

Walter TC and Boxshall G (2020) World of Copepods database. Oithona similis Claus, 1866. Accessed through: World Register of Marine Species at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=106656 Accessed online 22 January 2020.