[3] The mantle of D. opalescens is not fused to the head and its body is 4 to 5 times longer than it is wide, with fins equal in both length and width.

[5] The life cycle of D. opalescens has four stages: eggs, hatchlings (called paralarvae), juveniles, and adults.

Females insert the egg capsules into the sand with a sticky substance that anchors them in place so that the ocean surge can ventilate them.

Through a series of trial and error as these 2–3 mm ML hatchlings learn to eat copepods and other plankton in the first months of their lives.

This daily migration coupled with the shear zone created by tidal and near-shore currents cause the hatchlings to become entrained within 3 kilometers of shore.

By the time D. opalescens reaches 15 mm mantle length (about 2 months old) they are strong enough to swim in shoals.

Originally it was thought that the adults died after spawning, as the egg beds were often littered with dead squid.

[6] Doryteuthis opalescens is a cannibalistic predator that feeds on smaller prey species such as fish, crabs, shrimp, mollusks, and other juvenile squids.

Doryteuthis opalescens itself is an important food source for many predators like larger fish, sharks, marine mammals, seabirds, and also humans.

Its predators include the California sea lion, blue shark, sail fish, striped tuna, Chinook salmon, black-throated diver, and Brandt's cormorant.

In Southern California landings begin in November and continue through April correlated with the greater mixing of winter storms.

Between 1998 and 2019, studies found that D. opalescens populations in more northerly U.S. Pacific Coast waters have increased significantly.