Thysanoessa inermis (Krøyer 1846)

A common krill of the subarctic Atlantic and Pacific, and adjacent Arctic seas

Subarctic in deeper coastal waters and shelf breaks; Common in Arctic waters near Pacific or Atlantic inflows, uncommon in central basins; Undergo diel vertical migrations, spending daytime near bottom or to maxiamum of ~500 m, night-time in surface waters

Primarily herbivourous, may feed on detritous when food scarse; During open-water periods feed on phytoplankton when abundant (shifting to small zooplankton when phyoplankton less abundant); An important prey item for fish, birds, seals and whales

Transparent, yellowish if rich in lipids, females might develop blue hue when spawning; Eyes round, rostrum pointed, photophores red; Anntennae lack lappet, carapace without denticle; well-developed spine on 6th abdominal segment

Females lay several clutches of eggs (140 per brood on average) during spring; Females require repeated mating after each molt to form new egg clutches; Life cycles is typcial: eggs, nauplius, metanauplius, followed by several stages of feeding calytopsis, and furcillia larvae; Juveniles resemble adults, and molt regularly while growing to adulthood over the first year of life; Life expectancy not known, likely 1-2 years

Differs from other Thysanoessa species by the presence of a dorsal spine on the last segment of the abdomen.

Amphiboreal species; found in the Barents Sea, White Sea, Kara Sea, Bering Sea, Sea of Okhotsk.

The last segment of the abdomen carries a dorsal spine. The front edge of the carapace is transformed into an elongate rostrum. Uropods are shorter than the telson.

Length up to 30 mm.

Important food source for herring.

Arctic to Gulf of Maine

upper and glacial epipelagic regions of the Gulf and estuary, and the upper Mesopelagic of the Gulf and estuary

depth in m: 200-300; horizontal distribution: amphiboreal species, N Pacific, N Atlantic