Gonatus fabricii (Lichtenstein 1818)

Introduction

Brief diagnosis:

A Gonatus with ...

• 3 hooks and one sucker proximal to large central hook on club.
• 2 large chromatophores on ventral side of head medial to eyes (see drawing).
  
  

  Gonatus fabricii. Drawing from Kristensen

Characteristics

1. Arms
1. Number of suckers in proximal half of each arm IV = 62 at 129 mmGL (neotype), range for all sizes- about 55-69.
2. Tentacles
   1. Clubs 12-20% of GL (15% in neotype).
   2. Club dactylus with suckers in 7-8 irregular series at base decreasing to 4  sucker series about half way out dactylus; suckers nearly same size in transverse series.
      
   3. Club ventral-marginal zone with 4 series of suckers in central region; medial suckers ca. one-half diameter of suckers of other three series. Occasionally 1-2 small suckers present as a partial fourth series.
      
   4. Club dorsal-marginal zone with 3-4 irregular series of suckers.
   5. Club medial zone with large central hook; small distal hook and proximal series with usually 3 small hooks and one sucker, with largest hook never closest to large central hook (i. e., hooks initially increase in size proximally). About a quarter of squid lack  sucker, about 10% have 4 hooks and one sucker and about 3% have 2 hooks only.
      

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      Figure. Oral view of the proximal hooks of the medial zone and suckers of the ventral-marginal zone of the club of G. fabricii, fresh. Photograph by M. Vecchione with transmitted light taken aboard the R/V G. O. SARS during the MARECO cruise to the central North Atlantic

   6. Total number of suckers (excluding terminal pad, medial zone) on tentacular club: 155-229.
   7. Median region of tentacular stalk between marginal series with usually 40-80 suckers (range 38-109).
   

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   Figure. Oral views of the tentacle and club of G. fabricii 129 mm GL, neotype. Top - Tentacle. Bottom - Enlargement of the tentacular club. Drawings from Kristensen (1981).

   

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   Figure. Oral view of the tentacular club of G. fabricii, fresh. Same club photographed above. Photograph by M. Vecchione.

3. Head
1. Radula
   1. All lateral teeth of radula smooth, without ridges.
   

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   Figure. Radula of G. fabricii, 106 mm ML. Drawing from Kristensen (1981).

2. Funnel
   1. Ventral pads of funnel organ about half as long as each rami of dorsal pad.
      
   

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   Figure. Funnel organ of G. fabricii, 129 mmML, neotype. Drawing from Kristensen (1981).
   

4. Pigmentation
1. Two unusually large chromatophores lie deep on the ventral surface of the head.
   

Comments

The above description, except for photographs, is from Kristensen (1981). More details of the description can be found here.

Life History

The mature egg, found in the vicinity of the ovary of a mature female, is nearly spherical and almost 5 mm in the longest axis (Kristensen, 1981). Egg masses have never been observed in nature.

Paralarvae of G. fabricii are most easily separated from the partially sympatric species, G. steenstrupi, by the presence two large chromatophores on the ventral surface of the head in G. fabricii vs none in G. steenstrupi. This difference distinguishes the adults as well.  The full chromatophore pattern of the paralarva is not known. The number of suckers on arms I-IV is useful at sizes greater than 13 mm ML as is the form of the funnel organ in all but smallest paralarvae. The paralarval stage appears to end at about 20 mm ML which corresponds with hook development and movement into deeper water (Falcon, et al., 2000).

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Figure. Ventral views of growth stages of G. fabricii showing the head chromatophores and the form of the funnel organ. Drawings from Falcon, et al. (2000).

Distribution

Type locality: The neotype was taken at the entrance of Amerdloq Fjord at Holsteinsborg (approximately 67°N, 54°W), West Greeland, 250-285 fms.

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Figure. Distribution of Gonatus spp. in the North Atlantic. Blue - G. steenstrupi. Red - G. fabricii. General map with dots and triangles from Kristensen (1981). Red and blue lines based mostly on paralarvae, from Falcon, et al. (2000).

References

Falcon, L. I., M. Vecchione and C. F. E. Roper. 2000. Paralarval gonatid squids (Cephalopoda: Oegopsida) from the mid-north Atlantic Ocean. Proc. Biol. Soc. Wash., 113: 532-541.

Kristensen, T.K. 1981. The Genus Gonatus Gray, 1849 (Mollusca: Cephalopoda) in the North Atlantic. A Revision of the North Atlantic Species and Description of Gonatus steenstrupi. Steenstrupia, 7(4):61-99.