1. Arms
1. Hooks in two medial series on arms I-III.
   
   
2. Tentacles
1. Tentacles present in subadults.
2. Tentacular club with one or more hooks in median line; one greatly enlarged.
3. Proximal locking-apparatus of club with suckers and knobs medial to 4-6 large ridges and grooves, and usually several smaller ones.
   

   Figure. Oral view of tentacular club of G. californiensis, 315 mm GL, immature female, preserved. Photograph of preserved club by R. Young.

3. Head
1. Radula with 5 teeth in transverse row.
   
   
4. Mantle
1. Mantle tissue muscular or flabby depending on species.
   
   
5. Fins
1. Fins sagittate, drawn out posteriorly into a short tail.
   
   
6. Photophores
1. Ocular photophores present only in G. pyros.

Comments

Many of the species characteristics are found on the tentacles. The tentacles are complex and for descriptive purposes the club and stalk are divided into various zones, regions and series as follows:

The following table compares some characteristics of subadult species of Gonatus. The most useful character states are indicated in bold-red. The table doesn't separate all species.

Species / Character	Habitat	Ocular light organs	Proximal club hooks	Distal club hook	Medial suckers of tentacular stalk	Suckers on club	Club suckers of dorsal- and ventral marginal zones merge proximally.	Arm II< III length	Club length
G. antarcticus	Antarctic waters	No	Yes	Yes	120-140	250-315	No	40-50% ML	16-17% ML
G. berryi	North Pacific	No	Yes	Yes	0-2	159-181	No	60-70% GL	30-37% GL
G. californiensis	North Pacific	No	Yes	Yes	40-80	215-270	No	46-53% GL	17-24% GL
G. fabricii	North Atlantic	No	Yes	Yes	38-109	155-229	No	53-59% GL	12-20% GL
G. madokai	North Pacific	No	Yes	Yes	Many	?	Yes	90% ML	20% ML
G. middendorffi	North Pacific	No	No	Yes	Few	?	No	50% ML	10% ML
G. onyx	North Pacific	No	No	No	0-27	160-200	No	48-54% GL	20-25% GL
G. oregonensis	North Pacific	No	Yes	Yes	70	295-370	No	59-63% ML	21-30% ML
G. pyros	North Pacific	Yes	Yes	Yes	50-125	151-184	No	60-70% GL	20-25% GL
G. steenstrupi	North Atlantic	No	Yes	Yes	75-165	190-225	No	50-70% GL	20-36% GL
G. ursabrunae*	North Pacific	No	?	?	?	?	?	42-56% ML	13-25% ML

*Known only from juveniles but with distinctive relative sucker sizes on arms and club dactylus.