Dichotomous Key/Oegopsida

1

 * Buccal connective to arms IV
 * Dorsal - 2
 * Ventral - 3

2

 * Funnel locking-cartilage
 * Straight - 4
 * Inverted T - ../Ommastrephidae/

3

 * Carpal locking-apparatus
 * Present - 12
 * Not present - 13

4

 * Gladius conus
 * Present - 5
 * Not present - 6

5

 * Anterior fin attachment
 * Mantle - 8
 * Gladius - 7

6: Histioteuthids

 * Comparative eye size
 * Equal - Psychroteuthis glacialis
 * Unequal, left eye larger - ../Histioteuthidae/

7: Enoploteuthids

 * Hooks on tentacular clubs
 * Present - 9
 * Not present - 10

8

 * Free posterior fin lobes
 * Present - ../Neoteuthidae/
 * Not present - ../Architeuthidae/

9

 * Photophores on eyeballs
 * Present - 11
 * Not present - Ancistrocheirus lesueurii

10

 * Hooks on arm pairs I - III
 * Present - ../Pyroteuthidae/
 * Not present - ../Lycoteuthidae/

11

 * Photophores on mantle
 * Present - ../Enoploteuthidae/
 * Not present - ../Pyroteuthidae/

12
Brachioteuthidae

Cranchiidae

Gonatidae

Cycloteuthidae

Onychoteuthidae

Thysanoteuthidae

13

 * Secondary tentacular club
 * Present - 14
 * Not present - 15

14: Chiroteuthids

 * Number of series of suckers
 * Six (on at least one arm) - 20
 * Other than six (on any arm) - 18

15

 * Proximal region of manus of club greatly expanded
 * Present - ../Brachioteuthidae/
 * Not present - 16

16: Lepidoteuthids

 * Tentacles
 * Absent or reduced in adults - 17
 * Present - ../Pholidoteuthidae/

17

 * Number of hooks
 * Two or fewer - Lepidoteuthis grimaldii
 * Many, in two series - ../Octopoteuthidae/

18

 * Doratopsis paralarva
 * Present - ../Chiroteuthidae/
 * Not present - 19

19

 * Shape of distal ends of tentacles
 * Vermiform - Magnapinna pacifica
 * Other - 21

20

 * Comparative arm length
 * All arms comparable - Batoteuthis skolops
 * Arm pairs I - III much longer than others - Joubiniteuthis portieri

21

 * Ink sac
 * Present - ../Mastigoteuthidae/
 * Not present - ../Promachoteuthidae/