Gonatus madokai was described by Kubodera and Okutani (1977) based on a large holotype (329 mm ML) and two juvenile paratypes (72 mm DML) with three additional specimens (40-63 mm ML) collected from the subarctic waters of the northwestern North Pacific.

Morphological changes with growth of this species were well described (Kubodera and Okutani 1977). G. madokai is one of a few gonatids that can be identified almost throughout its life.

Diagnosis

A Gonatus with ...

• pronouncedly long arms (ca. 90% of ML), long tail (ca. 20% of ML) and soft body.
• large fins (FL>1/2ML), sagittate with round sides (FW=83% of FL).
• tentacle club with a central large hook, a middle-sized hook distal to the central hook and five small hooks in a line proximal to the central hook.