Atlantic Pygmy Octopus

O. joubini are found in the warm temperate to tropical waters of the Atlantic, thriving in temperatures ranging from 18 to 25 °C (64 to 77 °F). They are benthic and are typically found on soft, muddy substrates around 10 to 15 m (33 to 49 feet) deep. Many laboratory experiments have shown that O. joubini prefer to remain hidden or, in the case of a tank environment, close to the sides of the enclosure. This behavior is presumably for protection against outside predators, though no literature describes specific predators of the O. joubini. In many instances, O. joubini observed in their natural habitat are found hidden in empty soda cans, and some researchers even obtained them by collecting soda cans from the ocean floor. They prefer to shelter in small cavities on the ocean floor and compete for viable crevices with many other animals, including mantis shrimp such as N. bredini.

O. joubini in captivity exhibit highly varied broods ranging from 140 to over 2,500 eggs. They can reach sexual maturity at a very small size, though most spawning adults were at least 30 mm (1.2 inches). Females typically began to lay a new set of eggs when the oldest eggs began to hatch. The key characteristics that differentiate O. joubini from O. mercatoris, and other unidentified pygmy octopuses, is the size of the eggs and its color. While varying in size, fully developed eggs range from 2.9 to 4.8 mm (0.11 to 0.19 inches), and are overall smaller than other species that were studied, informally referring to them as the "small egg species" that is most representative of the original O. joubini Robson holotype. Additionally, O. joubini appear to have a reddish-orange color that is more distinct than the larger egged species.