Illex is formed by four taxa distributed throughout the Atlantic Ocean (I. argentinus, I. coindetii, I. illecebrosus and I. oxygonius), whose identification and phylogenetic relationships based on morphological characters remain controversial.They are found in the northwest Atlantic Ocean, from off the coast of eastern North America to Greenland, Iceland, and west of Ireland and the United Kingdom.

The squid is reddish brown to purple in color and there is higher opacity in the head and mantle while the rest of the body are yellowish green tinted.

[11] The months for hatching range from June to December where it is more prevalent in July, August, September, October and November.

[12] Even so, the condition of the habitat also affects the differing growth rate of both sexes as male grow faster than females in Newfoundland and Nova Scotian waters.

It is found that northern shortfin squid who lives in warmer waters grow more rapidly especially in the Mid-Atlantic region.

[14] Northern shortfin squid has developed behavior such as ink jetting,[15] schooling and camouflaging as protection to prevent predation by larger fish species such as bluefin tuna, red and silver hake.