Thysanoessa raschii (M. Sars 1864)

The most widespread Arctic krill

Transparent, yellowish if rich in lipids, females might develop blue hue when spawning; Eyes round, rostrum pointed, photophores red; Anntennae lack lappet, carapace with 1 small denticle; abdomen without keel-spines

Panarctic and subarctic in coastal waters (above 200m); Can be abundant in coastal embayments; Most common in Arctic waters near Pacific or Atlantic inflows, uncommon in central basins; Undergo diel vertical migrations, spending daytime near bottom, night-time in surface waters

Females lay several clutches of eggs during summer; 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 2-3 years

Primarily herbivourous, may feed on detritous when food is scarse - known to feed directly on under-ice algae; 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

Differs from other Thysanoessa species by the presence of 2 spines on the sides of the carapace

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

The lateral edges of the carapace carry a small spine on each side. The last segment of the abdomen does not carry a spine.

Length up to 30 mm.

Thysanoessa raschii, sometimes known as Arctic krill, is one of the most common euphausiid species of the subarctic and Arctic seas. They may reach 20–25 millimetres (0.8–1.0 in) long, and are sexually mature above 14 mm (0.6 in).

T. raschii is a major prey item of several taxa, planktivorous fishes and marine mammals. It is also a common prey item of seabirds, including shearwaters.

This species goes through a number of stages in its development. Roderick Macdonald defined the characteristics of fourteen stages, or 'furcilia'.

upper and glacial of the Gulf and estuary

depth in m: 0-200; horizontal distribution: amphiboreal species, N Atlantic, N Pacific