Mastigoteuthis magna group

Introduction

M. magna-group is very distinctive and its members cannot be easily confused with any other Mastigoteuthis. Squid in this group can be relatively common in warm temperate to tropical waters. One form is known only from Subantarctic waters.

Brief diagnosis:

A Mastigoteuthis with ...

• flask-shaped funnel locking-apparatus.
• very small (0.05 mm) tentacular club suckers. 

Characteristics

1. Arms
   
   1. Largest arm suckers in mid-arm rather than at or near arm base.
      
      
2. Tentacles
   1. Tentacular club suckers of uniform size throughout
      
   2. Tentacular club suckers extremely small, ca. 0.05 mm in diameter.
   

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   Figure. Oral view of the mid-region of the tentacular club of M. magna, 160 mm ML, preserved. The red dots are the suckers. Photograph by R. Young.

3. Head
   1. Funnel pocket absent.
   

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   Figure. Ventral view of head and funnel of M. microlucens. showing the absence of a deep pocket between the funnel-adductor muscles. Photograph by R. Young. 

4. Funnel
   1. Funnel with flask-shaped locking-apparatus.
   

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   Figure. Frontal and slightly oblique view of the funnel locking-groove of M. magna. Photograph by R. Young.

5. Fins
   
   1. Fin length usually 55-65% of ML.
      
      
6. Tubercules
   
   1. Tubercules absent from the integument.
      
      
7. Photophores and pigmentation
   1. Integumental photophores absent or microscopic in size (ca. one third diameter of integumental photophores of other members of the family - see M. microlucens).
      
   2. Pigment mostly in densely spaced chromatophores (possible exception in Mastigoteuthis type beta).
      
   

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   Figure. Frontal view of the skin of M. magna, under high magnification. Photograph by M. Vecchione.

Comparison of "species"

Here we compare the structure of the arm suckers (club suckers are similar in all forms), the funnel locking-apparatus, photophores and pigmentation of the three forms. Other differences exist (eg, beaks) but these most apparent ones.

1. Arm suckers: M. magna suckers have smooth inner rings although a hint of teeth can sometimes be seen in parallel lines on the ring. Mastigoteuthis "type beta" has small distinct teeth on the distal margin of the inner ring while M. microlucens generally has a few broad, rounded teeth, fused together over most of their lengths.
   


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Figure. Oral or oral-oblique views of large arm suckers of members of the M. magna-group. Left - M. magna, North Atlantic. Middle - Mastigoteuthis "type beta", Subantarctic Pacific. Right - M. microlucens, Hawaiian waters, central N. Pacific. Photographs by R. Young.

2. Funnel locking-apparatus: M. magna has a straight, anterior groove and a broad, posterior cup. Mastigoteuthis "type beta" has a broad groove that flares posteriorly and a rather elongate, posterior cup. M. microlucens has a slender a slender, anterior groove and a rather elongate, posterior cup. These features are often easier to recognize, in reverse, that is in the mantle component of the locking-apparatus.
   


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Figure. Frontal views of the mantle components of the funnel locking apparatuses in the members of the M. magna-group. Left - M. magna, North Atlantic. Middle - Mastigoteuthis "type beta", Subantarctic Pacific. Right - M. microlucens, Hawaiian waters, central N. Pacific. Photographs by R. Young.

3. Photophores: Photophores are known only in M. microlucens.
   
   
4. Pigmentation: Pigmentation is poorly understood except in M. magna which is covered with a dense array of red chromatophores. Mastigoteuthis "type beta" appears to be lightly pigmented and may lack chromatophores. M. microlucens is pigmented similar to M. magna but pigment may not be as dense in young individuals of M. microlucens.
   

Comments

The specific status of Mastigoteuthis "type beta" is uncertain since only one individual is known and its pigmentation, its most distinctive feature, is uncertain due to some damage during capture.