[8] Gigantocypris are ubiquitous in open oceans around the world, ranging from tropical to polar regions.

[6][11] Gigantocypris agassizii is essentially a widespread Pacific species, and Gigantocypris muelleri a widespread Atlantic and Southern Ocean species, but there are also a few possible records of the former in the Atlantic, and a few records of the latter in the Pacific and Indian oceans.

[8] Depending on the exact species, living individuals typically are orange, orange-red or violet-red,[6][15] but they can also be colourless.

[17] Despite living in the darkness below the sunlight zone, they are equipped with a pair of large eyes which, rather than using lenses to focus light onto a retina, use parabolic mirrors.

[18] The parabolic mirror eyes typically have a diameter of about 3 mm (0.12 in), look out through transparent sections of the carapace,[19] and appear silvery or golden in colour.

[7][15][22] Exactly how they catch their prey is unclear, but studies show that the outer part of their mandibles can be extended out through the slit (opening) of their globular carapace.

[7] They have a near-neutral buoyancy (marginally negative, sinking) and are able to swim smoothly (not in jerks) at a relatively high speed, indicating that they are active predators.

[10] They sometimes fall prey to other animals such as squid,[23] fish like grenadiers and chub mackerels,[24][25] and prions.

[26] The female Gigantocypris has a brood pouch, located inside the carapace, in which the eggs and embryos develop.