Ornithoteuthis antillarum has a thin, elongated and muscular mantle which ends in a long, thinly-pointed tail.

[3] The tentacular clubs have a sucker-bearing region which is approximately half of the length of the tentacles with large suckers on the manus with 18-20 widely separated sharp, round and curved teeth on the margin while the suckers on the dactylus are larger in the ventral series and smallest in the dorsal series.

Sampling also suggests that O. antillarum lives above the seabed during the day, dispersing upwards at night, a partial diel migrant.

[3] The sex ratio is 1:1[1] and as the population matures it is believed that they undergo a spawning migration into areas associated with sea mounts.

An individual with a mantle length of 140 mm was photographed from a submersible at 684 m in depth and a water temperature of 10.7 °C in the Bahamas eating an adult bristlemouth Gonostoma elongata, a midwater fish.

[3] O. antillarum has a number of predators and these include epipelagic and mesopelagic fishes and they have been recorded in the diets of fish such as common dolphinfish (Coryphaena hyppurus), Atlantic sailfishes (Istiophorus albicans), skipjack tuna (Katsuwonus pelamus), white marlin (Tetrapturus albidus), albacore (Thunnus alalunga), yellowfin tuna (Thunnus albacares), bigeye tuna (Thunnus obesus), swordfish (Xiphias gladius).

With bony fish, O. antillarum are the most important component of the winter diet of yellowfin tuna off Brazil.

It is parasitised mainly by didymozoid trematodes, however, the intensity of infection is much reduced compared to same-sized specimens of Sthenoteuthis pteropus.