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 - wikipedia:en: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 - wikipedia:en: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 - wikipedia:en:Lepidoteuthis grimaldii
  • Many, in two series - Octopoteuthidae

18

• Doratopsis paralarva
  • Present - Chiroteuthidae
  • Not present - 19

19

• Shape of distal ends of tentacles
  • Vermiform - wikipedia:en:Magnapinna pacifica
  • Other - 21

20

• Comparative arm length
  • All arms comparable - wikipedia:en:Batoteuthis skolops
  • Arm pairs I - III much longer than others - wikipedia:en:Joubiniteuthis portieri

21

• Ink sac
  • Present - Mastigoteuthidae
  • Not present - Promachoteuthidae