Gonatus antarcticus Lönnberg 1898

Introduction

Gonatus antarcticus was described by Lonnberg (1898) based on a stranded specimen near the Straits of Magellan (mm ML). He stressed that G. antarcticus difffered markedly from G. fabricii, which was the sole Gonatus species known at that time from the northern North Atlantic, by having greatly reduced marginal suckers, compressed hooks of arms I-III, and a little broader and differently shaped gladius. These characters stressed by Lonnberg may be due the comparison with the description of G. fabricii which was based on young individuals.

Diagnosis

A Gonatus with ... 

• large-size, very slender mantle (MW=17-18% ML), very long tail (ca. 20% of ML) and soft body.
• long, narrow fins (FL=1/2ML), sagittate with round sides (FW=83% of FL).
  
• long stout tentacles and small tentacle clubs (TCL=16-17% of ML)
  
• tentacluar club with central large hook, middle-sized hook distal hook and 3-4 small proximal hooks with distal one largest and sizes decreasing proximally.

Characteristics

1. Arms
1. Short (40-50% of ML), thick amd muscular.
2. Arm formula IV, II=III, I, but differences in lengths not prominent.
3. Arm IV with thin lateral keels and arm III with swimming keel along entire lengths.
4. Number of hooks and suckers on 1/2 arm III 20-21 and 21-22, respectively.
   
   

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   Photo. Gonatus antarcticus (ca. 22cm ML): deposited in South African Museum, Cape Town. Lavel indicates this specimen was identified into G. fabricii but judging from the locality this specimen should be G. antarcticus.

2. Tentacles
   1. Tentacle long (TL=ML) with relatively small club (TCL=16-17% ML).
      
   2. Large central hook with medium-sized distal hook.
   3. 3-4 hooks proximal to central large hook, distal one largest and decreasing in size rapidly proximally.
      
   4. Numerous small suckers on the median portion of the tentacular stalk.
      
   

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   Figure. Oral views of the tentacle and club of G. antarcticus. Top - Tentacle, 230 mm ML, NSMT-Mo 63957. Drawings from Kubodera & Okutani (1986). Bottom - Club, 113 mm ML. Photograph by R. Young.
   

3. Head
1. Almost squarish in shape, slightly narrower than mantle opening.
2. Funnel cartilage lanceolate in shape; nuchal cartilage rectangular with three grooves.
   
   
4. Fins and tail
1. Fins long, narrow (FL=1/2ML), sagittate with round sides (FW=83% of FL).
2. Long tail (ca. 20% of ML).
   
   
5. Photophores
1. Photophores absent.

Comments

Gonatus antarcticus is considered to be closely related to Gonatus species in the North Atrantic, i. e., G. fabricii and G. steenstrupi on the basis of external morphology. Imber (1978) considered that G. californiensis might be a synonym of G. antarcticus without reliable information. Tentacluar club structure and number of suckers on the tentacular stalk of G. californiensis apparently differ from G. antarcticus. Complete absence of Gonatus in  tropical waters indicates that this group has a distinct bipolar distiribution. Imber (1978) also described G. phoebetriae based on a single lower beak form the stomach contents of sooty albatross from off New Zealand. However, the validity of G. phoebetriae is very dubious due to incomplete comparison among beaks in the families and considered to be a species dubium. G. antarcticus is the sole Gonatus species distributed in the southern hemisphere.

Distribution

The distribution of G. antarcticus is primarily in the Atlantic sector of Antarctic waters around the Antarctic Convergence at  40 S. More details of the distribution are found here.

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Figure. Distribution of G. antarcticus. Dark pink area indicates known range; this species may have circum-antarctic distribution. Chart modified from Okutani (2005).

References

Kristensen, T. 1981. The genus Gonatus Gray, 1849 (Mollusca: Cephalopoda) in the North Atlantic. A revision of the North Atlantic species and description of Gonatus steenstrupi n. sp. Steenstrupia, 7(4): 61-99.

Kubodera, T. and T. Okutani. 1986. New and Rare Cephalopods from the Antarctic Waters. Memoirs of National Institute of Polar Research, Special Issue, 44:129-143.

Okutani, T. 2005. Cuttlefishes and squids of the world. Publication for the 40th Aniversary of the Foundation of National Cooperative Association of Squid Processors. 253pp.