Members of Sthenoteuthis are the dominant ommastrephid squids in tropical waters of the world's oceans and are commonly seen at the ocean's surface at night. They range in size from ca. 100 mm ML to 650 mm ML.

Brief diagnosis:

An ommastrephin with ...

• Large aggregation of subcutaneous photophores forming a dorsal photophore patch on anterodorsal region of mantle.

Circumglobal in tropical and subtropical, occasionally in temperate waters. S. oualaniensis is found in Pacific and Indian Ocean waters and S. pteropus in Atlantic Ocean waters.

1. Arms
   1. Arms tips in subadults not unusually attenuate; arms I with 20-30 pairs of suckers.
      
   2. Hectocotylus with pores. A fully developed pore passes through the protective membrane.
   3. Width of ventral protective membrane of arm III approximately equal to arm width.
      
      
2. Tentacles
   1. Largest club suckers with small pointed teeth and one large pointed tooth in each quadrant.
   
   

   Figure. Oral view of inner ring of largest club sucker of S. oualaniensis. Drawing from Roeleveld (1988).
3. Funnel/mantle locking-apparatus
   1. Mantle locking-apparatus with anterior bifurcation.
      
      
4. Photophores
   1. Small subcutaneous photophores on ventral surfaces of mantle, head and arms III-IV (see photographs on Ommastrephinae page).
      
   2. Large, oval, dorsal photophore patch composed of dense aggregaton of subcutaneous photophores on mantle near anterior end.
      
   3. Luminous patch on ventral surface of each eyeball.
      
   4. Two photophores on ventral surface of intestine in paralarvae and juveniles.
   
   
   

   Figure. Dorsal and dorsal-oblique of the dorsal photophore patch in S. oualaniensis with various stages of concealment. Top - Photophore patch (white area) mostly visible. Middle - Photophore patch almost completely concealed by chromatophores. Typically in preserved squid, the patch is not seen due to chromatophore cover. Bottom left - Photophore patch half partially covered and half uncovered. Photographs by R. Young. Bottom right - Cleared and stained portion of the mantle showing the dorsal photophore patch and the tip of the gladius. Scale bar is 3 mm. Photograph from Kishimoto and Kohno (1992).

Comparison of species

	Funnel/mantle locking-apparatus fused
Sthenoteuthis oualaniensis	Yes
Sthenoteuthis pteropus	No

Depth range based on 133 specimens in 2 taxa.
Water temperature and chemistry ranges based on 122 samples.

Environmental ranges
  Depth range (m): 3 - 914
  Temperature range (°C): 7.076 - 28.444
  Nitrate (umol/L): 0.008 - 40.784
  Salinity (PPS): 34.193 - 36.072
  Oxygen (ml/l): 0.272 - 4.979
  Phosphate (umol/l): 0.122 - 2.956
  Silicate (umol/l): 0.906 - 61.599

Graphical representation

Depth range (m): 3 - 914

Temperature range (°C): 7.076 - 28.444

Nitrate (umol/L): 0.008 - 40.784

Salinity (PPS): 34.193 - 36.072

Oxygen (ml/l): 0.272 - 4.979

Phosphate (umol/l): 0.122 - 2.956

Silicate (umol/l): 0.906 - 61.599
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.