This species can be found inhabiting shallow, inshore waters around central China, South Korea, and Japan.

[6] The type specimen was collected off Kadsiyama in Tokyo Bay and is conserved at the Musee Zoologique in Strasbourg.

[2] The distribution of this species includes the waters off South Korea and northern Australia, as well as the Japanese islands of Honshu, Kyushu, and southern Hokkaido.

The buccal mass is used to break through hard exoskeletons, secrete digestive fluids, and then remove the softened flesh of prey.

[10] There is also evidence of a sex-specific cognitive bias in I. paradoxus, such that females more often than males overestimate the size of prey they will be able to successfully attack.

[4][12] The sperm become activated by seawater, and will swim to the seminal receptacle around the female's buccal mass on the ventral mantle, where they will be stored until spawning and fertilization.

[13] The female can mate with multiple males and retain sperm from each before adhering to a substrate such as seagrass to spawn.

[6] Once the female has mated, either with one male or several, she can use her buccal mass to pull spermatangia off her body individually to get rid of as many as she chooses.

[18] A possible explanation for female preference of small and fast copulating males could be that predation risk is decreased with shorter time spent in copula and less attention drawn with smaller body size.

During copulation, males have been observed directing their spermatangia by the right hectocotylus to different locations on the female's body (such as different arm crown bases) per spermatophore ejaculation.