Diagnosis

A Gonatus ...

• without two large, deep chromatophores on the ventral surface of the head.
  
• with 4-5 hooks (largest most distal) and 1 sucker proximal to large central hook on club.
• with about 50 on median portion of tentacular stalk.
  

1. Arms
1. 46-57 suckers in proximal half of each arm IV.
   
   
2. Tentacles
   1. Clubs 20-36% of GL (25% in holotype).
   2. Club dactylus with 7-8 irregular sucker series at base becoming 4 series about half way out dactylus.
   3. Club ventral-marginal zone with 4 series of suckers in central region; medial suckers ca. one-half diameter of suckers in two marginal series. Largest suckers slightly smaller than largest arm suckers.
      
      
      

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

   4. Club dorsal-marginal zone with suckers in 4 irregular series.
   5. Club medial zone with large central hook; medium distal hook and proximal series with usually 4 small hooks and a sucker. Hooks decrease in size proximally. Sometimes the sucker replaced by 5th hook. Sometimes 6 hooks and rarely only 3 hooks present.
   6. Total number of suckers (excluding terminal pad, medial zone) on tentacular club: 190-225.
   7. Median region of tentacular stalk between marginal series with about 75-165 suckers.
   
   
   

   Figure. Oral views of the tentacle and club of G. steenstrupi, 94 mm GL, holotype. Top - Tentacle. Bottom - Enlargement of the tentacular club. Drawings from Kristensen (1981).

   
   

   Figure. Oral view of a tentacular club of a late juvenile G. steenstrupi, alive. The proximal suckers are just beginning to transform into hooks. Photograph by David Shale.

3. Head
1. Radula
   1. Lateral teeth of radula profiled by a ridge.
      
   

   Figure. Radula of G. steenstrupi, 57 mm ML. Drawing from Kristensen (1981).
   

2. Funnel
   1. Ventral pads of funnel organ about two thirds length of each ramus of dorsal pads
      
   

   Figure. View of the funnel organ of G. steenstrupi, holotype, 94 mm GL. Drawing from Kristensen (1981).

4. Pigmentation
   1. Two unusually large chromatophores absent from the ventral surface of the head.

Comments

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

All of the above features are useful in separating G. steenstrupi from G. fabricii. However, the lack of head chromatophores and the presence of usually 4 hooks proximal to the large central hook of the club are the easiest to identify.

European waters (ERMS scope), Northern North Atlantic, Portuguese Exclusive Economic Zone, Spanish Exclusive Economic Zone, United Kingdom Exclusive Economic Zone

Type locality: "east of Rock All, Northeast Atlantic". This is presumably Rockall trough so the locality would be in the vicinity of 57°N, 12°W

epi-mesopelagic

Depth range based on 14 specimens in 1 taxon.
Water temperature and chemistry ranges based on 12 samples.

Environmental ranges
  Depth range (m): 992 - 3458.5
  Temperature range (°C): 2.878 - 4.365
  Nitrate (umol/L): 16.616 - 18.394
  Salinity (PPS): 34.904 - 34.982
  Oxygen (ml/l): 5.915 - 6.416
  Phosphate (umol/l): 1.092 - 1.169
  Silicate (umol/l): 10.743 - 15.395

Graphical representation

Depth range (m): 992 - 3458.5

Temperature range (°C): 2.878 - 4.365

Nitrate (umol/L): 16.616 - 18.394

Salinity (PPS): 34.904 - 34.982

Oxygen (ml/l): 5.915 - 6.416

Phosphate (umol/l): 1.092 - 1.169

Silicate (umol/l): 10.743 - 15.395
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

Paralarvae of G. steenstrupi are most easily separated from the partially sympatric species, G. fabricii by the absence of two large photophores on the ventral surface of the head that distinguish the adults as well. 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).