While O. agassizii exists across a wide depth range, heavier octopuses generally live 700 meters or more from the ocean's surface.

The largest specimen, a male, had a mantle (the body not including the octopus' arms) reaching 63 mm, a little under two and a half inches.

A study in a sister species, Opisthoteuthis grimaldii, observed them using the fins to maintain a vertical position in the water relative to the mantle and sea floor.

Opisthoteuthis agassizii exhibit extended spawning, and the number of egg cells in a female does not appear to correlate with body mass like in most octopus species.

[7] Opisthoteuthis agassizii are predacious and tend to eat benthic prey, such as amphipods and polychaetes, but their diet frequently expands to include copepods, decapods, crustaceans, and even microbivalves and microgastropods.

There is a slight shift in primary prey as they grow in size; a study found that O. agassizzi under 500g fed mainly on amphipods, while those above 500g ate more polychaetes.

[10] Most of their time is spent along the seafloor, hunting prey and crawling using their eight arms, but O. agassizii can swim like all octopuses are capable of doing.

A study on a related species also showed similar fins being used to aid in buoyancy and ballooning, a common defense mechanism in octopoda.

[9] Cirrate octopods cannot, however, swim via jet propulsion, and thus O. agassizii specimens use their fins to drift or pump their arms in contractions to move in a more controlled fashion.

The most extensive work has been done by Piertney, who used ribosomal DNA sequencing to place the Opisthoteuthidae as a sister family of Grimpoteuthis, Luteuthis, and Cryptoteuthis.