The males have a hectocotylus in which the upper half of left dorsal arm is modified with enlarged pedicels to the suckers which are densely packed to form 2 double rows of columnar structures and the suckers are reduced, having very small, fleshy, narrow openings.

There are a pair of saddle-shaped bioluminescent organs present in the inside of the mantle cavity on the ink sac.

[3] However, there is taxonomic uncertainty about the definition of E. morsei and other authorities have stated that this is a temperate species which is only found in the colder seas around Japan.

[1] Euprymna morsei is a shallow water species which spends the day buried in soft substrates and emerge at night to feed, using their bioluminescent organs to emit just enough light to disguise their silhouette from predators such as lancet fish (Alepisaurus ferox).

[1] Euprymna morsei is fished for food on a very small, local scale and sometimes taken as bycatch by fisheries.