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Containing group: Mastigoteuthidae

Introduction

The Mastigoteuthis species occur throughout much of the Atlantic, Indian and Pacific Oceans. At present we are confident of the separate species status of only two species: M. agassizii and M. psychrophila. However, character variation through the wide range of the group is apparent (see Comments) and we suspect that eventually more species will prove to be valid.

At present we refer to the tropical to temperate Indo-Pacific member as M. dentata, to the south temperate, tropical to boreal Atlantic member as M. agassizii (see the M. agassizii page for more details), and to the high-latitude southern form found in at least the South Atlantic and South Pacific as M. psychrophila.

Brief diagnosis:

Mastigoteuthids with ...

• numerous, small but easily seen integumental photophores.
  
• broadly spaced chromatophores.
  

Characteristics

1. Arms
   
   1. Arms III ca. 20% larger than arms I and approximately equal to arms II.
   2. Arm suckers largest near arm base.
      
      
2. Tentacles
   1. Club suckers vary in size and packing density depending on position on club; proximal and marginal suckers smallest.
   2. Largest club suckers 0.15-0.2 mm in diameter in large (about 80 mm ML or more) squids.
      
      
3. Head
   
   1. Funnel pocket present.
      
      
4. Funnel
   1. Funnel locking-apparatus ear-shaped with tragus but with or without antitragus; posterior margin of funnel lock deeply undercut.
      
      
5. Fins
   
1. Fin length (without tail) generally 55-65% ML; slightly broader than long.
   
   
6. Tubercules
   
   1. Tubercules absent from the integument.
      
      
7. Integument and photophores
   1. Integument with numerous, small (easily visible under the microscope)  photophores.
      
      

      Click on an image to view larger version & data in a new window

      

      Click on an image to view larger version & data in a new window

      
      

      Figure. Ventral view of M. agassizii photographed in a shipboard aquarium by David Shale on an NSF cruise with Marsh Youngbluth, Harbor Branch Oceanographic Institution, N.E. Atlantic waters. The original brilliant red color in the image has been reduced in Photoshop to accentuate detail. A double series of photophores shows best on the right (lower arm in photograph) ventral arm. ©

   The integument of species in the M. agassizii-group is complex and contains two elements in addition to the integumental photophores: (1) very small, whitish balls and (2) whitish rings surrounding chromatophores. Since the function of these two structures is unknown (we suspect that the latter may be a second category of integumental photophores), we call the first "white balls" and the second "ringed chromatophores" for descriptive purposes.

   2. Integument with chromatophores well sparated from one another (= scattered chromatophores).
      
   3. Ringed chromatophores present.
      
   4. Integument of the arms and head with numerous, very small (ca. 0.03 mm), white spheres (function unknown).
      
   

   Click on an image to view larger version & data in a new window

    

   Figure.  Ventral view of the head integument of M. agassizii, Gulf of Mexico, showing typical integumental photophores (bottom arrow) which lie deeply embedded in the skin, ringed chromatophores (top arrow) and white spheres. Non-ringed chromatophores are absent and most of the pigment is not in chromatophores. Photograph by R. Young.
   

   5. Eyeball photophores absent.
      
   6. Eyelid with very small eyelid photophore but, generally, distinctly larger than large integumental photophores of head.
      
      

      Click on an image to view larger version & data in a new window

      
      

      Figure. Left - Ventrolateral view of the head of a small M. dentata, 48 mm ML, Equatorial Pacific, preserved, showing the size of the eyelid photophore (arrow) relative to the integumental photophores of the head. Photograph by R. Young. Right - Lateral view of the eye of M. agassizii, western North Atlantic, alive, showing the eyelid photophore (white arrow) which is nearly invisible due to pigment cover. Black arrow points to the iris of the eye. ©
      

   More information on integumental photophores can be found here.

Comments

Integumental photophores are found in at least four species, but their morphology has only been studied in M. agassizii. The photophore has a large covering chromatophore that lies beneath vacuolated cells, a thick donut-shaped cup of photocytes and a central cord of cells that passes through the hole in the photocyte donut to the chromatophore.

The integumental phototophores of the M. agassizii-group appear superficially to be very similar to those of Mastigotragus pyrodes. However, the vacuolated cells above the covering chromatophore in M. agassizii give the impression that the photophore is sunken into the skin. Mastigotragus pyrodes also differs in lacking the ringed chromatophores and white spheres and has much more abundant chromatophores.

Comparison of species

Outer rings of club suckers have a complete whorl of pegs with lateral pegs enlarged in some species. The presence and size of enlarged lateral pegs depends on the absolute size of the sucker. Sucker size, howsever can vary with age and sucker position on the club. Smaller suckers are found proximally, distally at extreme tip and marginally on the club. Generally, the lateral pegs become enlarged at a sucker diameter of about 0.15 mm. Therefore if a large squid (ca. 80 mm ML or more) does not develop suckers of this size or larger, as in M. psychrophila, enlarged lateral pegs will not occur. This character is very important but is only useful in large squid.

M. psychrophila is most easily distinguished from other species of Mastigoteuthis by the arm IV photophore patterns (multiple irregular series vs two series), the differences in tentacle sucker dentition in large specimens (no enlarged pegs vs enlarged lateral pegs) and a slightly more pronounced antitragus in the funnel locking-apparatus. Of the remaining species, we recognize two of the five forms that have been described as separate species. These two, M. agassizii (temperate South Atlantic to boreal N. Atlantic) and M. dentata (tropical to temperate IndoPacific) are distinguished primarily by their geographic distribution. We compare the three species here:

• The funnel locking-apparatus of all three species.
  
• The club suckers of all three species. 
  
• The photophore patterns of all three species.

Nomenclature

We have placed three species, M. flammea,  M. grimaldii and M. schmidti, in synonymy with M. agassizii. See the M. agassizii page for more information on these species.