Under Construction

This genus contains the following 12 species:

Containing group: Gonatidae

Introduction

Gonatus, the most speciose genus in the family, has its highest diversity in the high North Pacific. These squids reach a maximum length of 39 cm ML.

Brief diagnosis:

A gonatid ...

• with one or more hooks in median line on tentacular club.

Characteristics

v

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.
   

   Click on an image to view larger version & data in a new window

   

   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. Posterior tip of mantle muscle separable from fins (not confirmed in most species). The tip of the tail (see arrow below) in Gonatus spp. is loosely attached to the mantle. The photograph below shows the fins apparently separating from the mantle tip. Although not visible in the photograph, transparent integument does extend between the tip of the mantle and the fins. The tip of the fins can also curve ventrally beneath the mantle tip. Presumably this unusual flexibility of the tip of the muscular mantle and fins increases manuverability.
   
   

   Click on an image to view larger version & data in a new window

   
   

   Figure. Ventrolateral view of Gonatus sp. Insitu ROV photograph at 701 m depth. Photograph © 2011 MBARI.

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.

Behavior

Some, at least, Gonatus spp. exhibit a "Parachutte posture" (see photographs below) similar to that seen is some other MBARI photographs of oceanic squids, which presumably reduces the sinking rate. In the upper left photograph, the squid is just entering into the posture. In the upper right photograph, the squid is in the posture and the squid is motionless with arms, tentacles and fins spread wide and the squid horizontally oriented. In the bottom photograph, the squid is just coming out of the posture. The squid held the posture for about 20 seconds. Presumably it would hold the it longer if not disturbed by the ROV.

Gonatus spp. often swim with their tentacle clubs locked together. The clubs are often locked both at the base of the clubs (carpal locking apparatuses) and at the tips of the club (presumably the circle of suckers that form the terminal pad). At the carpal locking apparatus we assume that the suckers involved of one club grasp the corresponding knobs of the other club. The terminal pad, however, has suckers but no knobs. The following photographs suggest how the latter lock is formed.

Life History

Brooding of egg masses in G. onyx (Seibel et al., 2000) [suspected in G. fabricii (Bjorke et al., 1997), and documented in G. madokai (Bower et al., 2012)] occurs in deep water. Such brooding behavior, rare in oceanic squids, may prove to be characteristic of all members of the genus and perhaps the entire family. The long brooding period demanded by cold temperatures in deep water and its resulting slow population turnover rate, presumably is offset, in evolutionary time, by low egg mortality in the vast, dark, lowly populated bathypelagic environment (see Seibel, et al., 2000). For more information on brooding behavior, go to the G. onyx page.

References

Bower, J. R., K. Seki, T. Kubodera, J. Yamamoto and T. Nobetsu. 2012. Brooding in a gonatid squid off northern Japan. Biol. Bull. 223: 259-262.

Nesis, K. N. (1982). Abridged dey to the cephalopod mollusks of the world's ocean. 385+ii pp. Light and Food Industry Publishing House, Moscow. (In Russian.). Translated into English by B. S. Levitov, ed. by L. A. Burgess (1987), Cephalopods of the world. T. F. H. Publications, Neptune City, NJ, 351pp.

Okutani, T. and M. R. Clarke (1992). Family Gonatidae Hoyle, 1886. P. 139-156. In: Sweeney, M. J., C. F. E. Roper, K. M. Mangold, M. R. Clarke and S. V. Boletzky (eds.). "Larval" and juvenile cephalopods: a manual for their identification. Smiths. Contr. Zool., No. 513.

Seibel, B. A., F. G. Hochberg, and D. B. Carlini. 2000. Life history of Gonatus onyx (Cephalopoda: Teuthoidea): deep-sea spawning and post-spawning egg care. Marine Biology 137 (3): 519-526.

Seibel, B. A., B. H. Robison and S. H. D. Haddock. 2005. Post-spawning egg care by a squid. Nature 438: 929.