Japanese gun squid body is conical, like a pen tube, so it is also commonly known as "pen tube octopus". It is small, the longest not more than 15 centimeters, the body is symmetrical, carcass length is four times the carcass width. The orbits on both sides of the head are large, and the eyes have pseudocornea on the outside, only a very small lacrimal hole connects with the outside world. There are 10 carpals in front of the head and around the mouth, of which 4 pairs are shorter, with two rows of suckers on the carpals, and the other pair of carpals is longer, with a tentacle, and the top of the tentacle is a spike, with 4 rows of suckers on the spike. Carpal fins long, more than 1/2 of carcass length, posteriorly recurved, terminal fins shaped, two fins connected in longitudinal rhombic shape. Body surface with nearly circular pigmented spots of varying sizes. Inner shell horny, transparent, lanceolate, slightly narrowed posteriorly. The body has an ink sac.