[3] The size of a fully grown O. ingens, inclusive of tentacles, is currently unknown.

Juveniles are presumed to live near the surface, until they reach a mantle length of approximately 200 mm, at which time they relocate to deeper water, and larger prey.

O. ingens exhibit sexual dimorphism, with females growing linearly twice as fast as males, and reaching a fully mature size of more than five times that of male counterparts.

[5][6] As such, deep water squid like M. ingens have the greatest known penis length relative to body size of all mobile animals, second in the entire animal kingdom only to certain sessile barnacles.

One of the most common findings is that juvenile squid (>200 mm ML) consume a greater percentage of crustaceans and cephalopods compared to their size than mature squid, which consume a large percentage of fish and virtually no crustaceans.