M. hjorti was originally described from five badly damaged specimens from the North Atlantic, then redescribed by Rancurel (1973) from three squid from the Gulf of Guinea. The species is distinctive and widely distributed but uncertainty exists on the taxonomic status of populations in other oceans.

Brief diagnosis:

A Mastigoteuthis ...

• with two photophores on each eyeball.
• with very large fins (length ca 90% of ML).

Limited molecular data is available for this species (see Mastigoteuthidae: Discussion of Phylogenetic Relationships).

1. Arms
   1. Arm III equals arm I in length (needs confirmation).
      
      
2. Tentacles
   1. Club suckers about equal sized except near tip.
      
      
3. Head
   1. Beaks. Description of the beaks can be found here in 2D.
   2. Beaks. Descriptions can be found here in 3D: Lower beak; upper beak.
      
   3. Funnel pocket absent.
      
      
4. Funnel
1. Funnel locking-apparatus with oval, slightly curved depression, posterolateral sides protude; without antitragus or clear tragus. Depression undercuts posterior margin.


Figure. Frontal views of the funnel/mantle locking-apparatus of M. hjorti. Left - Funnel component (uppermost), mantle component (lowermost). Drawing from Rancurel (1973). Left two photographs - Funnel component (left), mantle component (right), equatorial Pacific. Right two photographs - Funnel component (left), mantle component (right), 73 mm ML, eastern North Atlantic, 17°24'N, 22°57'W, NMNH 815489. Tissue stained with methylene blue stain. Photographs by R. Young.

5. Fins
1. Fins large; length about 90% of ML.
   
   
6. Tubercules
1. Large tubercules cover mantle, head, funnel and aboral surface of arms in subadults (tubercules are often lost during capture).


Figure. Left - Lateral view of head of M. hjorti showing tubercules and olfactory organ, 48 mm ML, western North Atlantic. Also visible are two lines on the head of the lateral-line analogue of cephalopods. Photograph by R. Young. Right - Scanning electron micrograph of mantle tubercles of M. hjorti, 93 mm ML, South Africa at 80°S, 05°E. Scale 0.1 mm. Photograph from Roper and Lu (1990).

7. Fins
1. Fins large, nearly the full length of the mantle. (see title photograph).
   
   
8. Photophores
1. Two large circular photophores on ventral surface of eyeball; no other photophores present.


Figure. Ventral view of damaged eye of a fresh M. hjorti, western North Atlantic. Arrows point to photophores. Photograph by M. Vecchione.

Comments

More information on the description of M. hjorti can be found here.

M. hjorti bears resemblance to M. cordiformis in the presence of large fins, skin tubercules, lack of a pocket between the bridles and the large trabeculate protective membranes on the tentacular clubs but differs in the presence of ocular photophores among other features.

Circum-equitorial, Gulf of Mexico

Type locality: North Atlantic at 36°N, 40°W; 32°N, 33°W; 36°05'N, 43°58'W. The species is also known from the central Pacific (pers. obs.), off South Africa (Roper and Lu, 1990) and the Indian Ocean (Nesis, 1987).

meso-bathypelagic

Depth range based on 25 specimens in 1 taxon.
Water temperature and chemistry ranges based on 25 samples.

Environmental ranges
  Depth range (m): 110 - 2510
  Temperature range (°C): 2.826 - 18.110
  Nitrate (umol/L): 3.246 - 34.258
  Salinity (PPS): 34.685 - 36.411
  Oxygen (ml/l): 1.831 - 6.192
  Phosphate (umol/l): 0.222 - 2.088
  Silicate (umol/l): 2.272 - 59.357

Graphical representation

Depth range (m): 110 - 2510

Temperature range (°C): 2.826 - 18.110

Nitrate (umol/L): 3.246 - 34.258

Salinity (PPS): 34.685 - 36.411

Oxygen (ml/l): 1.831 - 6.192

Phosphate (umol/l): 0.222 - 2.088

Silicate (umol/l): 2.272 - 59.357
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

Vecchione, et al. (2001) described a 6 mm ML paralarva which they assummed belonged to M. hjorti on the basis of a single large photophore on each eyeball. They described the paralarva as follows:

Mantle narrow, inserts on anterior end of fins. Fins ca. 25% of ML (excluding tail). Long, spike-like tail, nearly 3 times fin length. Skin mostly missing but fragments with scattered tubercules present. One light organ on ventral surface of each eye. Arm formula: II>I>IV>>III (arms III are minute buds). Tentacles long, thick, about 4 times length of arms II. Clubs with about 54 small suckers in 2 series proximally grading to 6 along "manus." Suckers end abruptly; tip with sucker anlagen.