Cycloteuthis sirventi Joubin, 1919

Introduction

Cycloteuthis sirventi is easily distinguished from species of Discoteuthis by the general shape which includes a tail. Maximum known size is 480 mm ML (Clarke, 1986). This is probably the most common member of the family but, nevertheless, little is known of its biology.

Brief diagnosis:

A cycloteuthid ...

• with a distinct tail.
• with a large visceral photophore.

Characteristics

1. Arms
   1. Large suckers from arm III with ca. 20 low, truncate teeth (larger distally) around entire margin.
      
      

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      Figure. Oral view of inner ring of large arm suckers of C. serventi. Left to right - Suckers from arms I - IV respectively. Drawing from Young and Roper (1969).

2. Tentacles
   1. Suckers nearly equal in size across manus of club.
   2. Suckers from club manus with ca. 20 teeth, pointed distally and truncated proximally.
      
      

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      Figure. Left - Oral view of tentacular club of C. serventi, 42 mm ML.  Drawing from Young and Roper (1969).
      

      

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      Figure. Oral views of tentacular club suckers of C. sirventi. Left - Manus sucker with outer ring intact. Middle - Manus sucker showing inner ring only. Right - Dactylus sucker showing inner ring only.Drawings from Young and Roper (1969).

3. Head
   
   1. Beaks: Descriptions can be found here: Lower beak; upper beak.
      
      
4. Mantle
   1. Tail present.
      
      
5. Fins
   1. Fins large, oval, length about 80% of ML in subadults.
      
      
6. Photophores
1. Large photophore on ink sac.
2. Irregular series of small photophores apparently at edge of iris; large photophore on ventral surface of eyeball.
   

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   Figure. Ventral view of the visceral nucleus of C. serventi. Drawing from Young and Roper (1969).

7. Gladius
   1. Gladius with a secondary conus.
      

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      Ventral view of the gladius of C. sirventi. Drawing from Young and Roper (1969).

Nomenclature

A second species, Cycloteuthis akimushkini Filippova, 1968, has been described. This description was based on a very large specimen and apparent differences between this species and C. sirventi may be due to size effects alone. This species is considered to be a synonym of C. sirventi at present.

Life History

C. serventyi has a very distinctive paralarva. The second arms are very long and a thick, transparent dermal layer is present in the integument. Each eye is on a stalk but, unlike many cranchiids, the optic lobe is attached to the central brain and long retinal nerves connect it to the eye.

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Figure. Ventral and dorsal views of a paralarva of C. serventyi, 8.1 mm ML, Hawaiian waters. The scale bar is 1 mm. Drawings by R. Young.

Distribution

Geographical distribution. Tropical and subtropical waters of the world's oceans.

Other Names for Cycloteuthis sirventi Joubin, 1919

• Cycloteuthis Joubin, 1919

References

Clarke, M. R. 1986. A Handbook for the Identification of Cephalopod Beaks. Clarendon Press, Oxford. 273 pp.

Filippova, J. A. 1968. A new species of the genus Cycloteuthis. Malacol. Rev., 1: 119-124.

Nesis, K. N. 1982. Abridged key to the cephalopod mollusks of the world's ocean. 385,ii pp. Light and Food Industry Publishing House, Moscow. (In Russian.). Translated into English by B. S. Levitov, ed. by L. A. Burgess (1987), Cephalopods of the world. T. F. H. Publications, Neptune City, NJ, 351pp.

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.