Discoteuthis discus Young and Roper 1969

Introduction

Discoteuthis discus is most easily separated from its congeners by the arrangement of photophores and the form of the funnel locking-apparatus.

Brief diagnosis: 

A Discoteuthis ... 

• with a diagonal groove in the funnel locking-apparatus.
• with a photophore at the ventral tip of  the mantle.
  
  

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

  
  

  Figure. Ventral view of D. discus, xx mm ML, Gulf of Mexico. Badly damaged trawl-captured squid. Note the general proportions and the fragile structure of the arms.. Photograph by Danté Fenolio.

Characteristics

1. Arms
   1. Arms weak, approximately subequal and 60-85% of ML.
   2. Large arm suckers with few low, broad, rounded teeth mostly on distal margin.
   

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

   

   Figure. Oral views of large arms suckers of D. discus, 45 mm ML. Left to right - Sucker of arms I-IV respectively. Drawing from Young and Roper (1969).

2. Tentacles
   1. Dactylus with suckers in four series throughout.
   2. Medial suckers on manus of club globular relative to D. laciniosa (inner ring height ca 60% of diameter compared to 35% of diameter).
      

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

      

      Figure. Left - Side views of large manus suckers from D. discus (45 mm ML) and D. laciniosa (56 mm ML, paratype). Right - Oral views of a large sucker from manus and a much smaller sucker from the dactylus of D. discus, 45 mm ML, showing dentition. Drawings from Young and Roper (1969).

   3. Largest club suckers with numerous low, flattened or rounded teeth around entire inner ring.
      
      

      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. Oral view of the tentacular club of D. discus. TOP - 53 mm ML, holotype. Drawing from Young and Roper (1969). BOTTOM - XX mm ML. Photograph by Danté Fenolio.

3. Head
   
   1. Beaks: Descriptions can be found here: Lower beak; upper beak.
      
      
4. Funnel
   1. Locking-apparatus with diagonally positioned groove.
      

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

      

      Figure. Frontal view of the funnel locking-apparatus of D. discus, 45 mm ML. Drawing from Young and Roper (1969).

5. Mantle
   1. Free anterior margin of mantle smooth (i.e., flaps lacking).
      
      
6. Photophores
   1. At least 4 organs on margin of eyelid.
   2. One dark, round organ on ventral surface near posterior tip of mantle.
   

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

   

   Figure. Ventral view of posterior tip of mantle and fins of D. discus, 53 mm ML, holotype. Drawing modified from Young and Roper (1969).

7. Gladius
   1. Conus absent.
   

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

   

   Figure - Ventral view of the gladius of D. discus, 53 mML, holotype, with cross-sections shown above. Drawing from Young and Roper (1969).

Life History

The smallest known D. discus is 16 mm ML (Young and Roper, 1969). At this size, the fins are about 60% of the ML and reach 98% of the ML in squid of 45 mm ML. Mature individuals are not known.

Distribution

The type locality is off Ghana, West Africa (03 deg 50'M. 02 deg 37'W) in the tropical East Atlantic. This species is known from the tropical and subtropical Atlantic and the central North Pacific (M. Seki, pers. comm.).

References

Young, R. E. and C. F. E. Roper. 1969. A monograph of the Cephalopoda of the North Atlantic: The family Cycloteuthidae. Smithsonian Contributions to Zoology No. 5:1-24.