Planctoteuthis oligobessa Young 1972

Introduction

Planctoteuthis oligobessa is a small species (maximum size = 76 mm ML). It can be separated from subadults of other members of the genus by the small fins and few suckers on arms IV. Little is known of its biology.

Brief diagnosis:

• 2-4 suckers on each arm IV.
• fin length 1/4 - 1/3 of ML.
  

Characteristics

1. Arms
   1. 2-4 suckers on each arm IV.
   2. Arm lengths: Arms I: 32-39% of ML (subadults); arms I: 24-25% of ML (adults); arms III: 47-61% of ML (subadults). arms IV: 121-135% of ML (subadults); arms II-IV 29-39% of ML (adults).
   3. Large arm suckers with 25-35 small, narrow, blunt teeth on distal 3/4 of ring.
      

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      Figure. Oral view of large arm suckers of P. oligobessa, 27 mm ML. A-D - Suckers from arm I-IV respectively.

2. Tentacles
   1. Clubs bilaterally symmetrical in shape.
   2. Club length 12-18% of ML.
   3. Suckers without teeth on inner ring.
   4. Clubs without keels.
      

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      Figure. Oral views of club sucker and club, 27 mm ML. Drawings from Young (1972).

3. Head
   
   1. Beaks: Descriptions can be found here: Lower beak; upper beak.
      
      
4. Funnel
   1. Locking apparatus with slender antitragus consisting of a single lobe.
      

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      Figure. Funnel locking apparatuses of P. oligobessa. Left - 27 mm ML. Drawing from Young (1972). Right - Subadult, off Southern California.

5. Fins
   1. Length 23-33% of ML.
6. Measurements

   	Paratype	Paratype	Holotype
   Sex	--	--	Female
   Mantle length	34	34	76
   Mantle width	11	11	28
   Fin length	7	8	14
   Fin width	12	--	--
   Length, arm I	12	11	19
   Length, arm II	15	15	27
   Length, arm III	18	16	29
   Length, arm IV	46	41	30
   Club length*	6	4	--
   Arm IV sucker count (left / right)	3 / --	3 / 2	2 / 3

   *Without carpus

Comments

Individuals of Planctoteuthis taken in trawls invariably show a broken gladius at the posterior end of the fin. The existence of a long and decorative tail was not known until ROV photographs captured insitu images. These images were taken by the Monterey Bay Aquarium Research Institute. The ventrally bulging eyes identify it as Planctoteuthis and the locality off California strongly suggests that it is P. oligobessa. The function of the tail is unknown although Vecchione et al. (1992) noted that the tail of Chiroteuthis (see Chiroteuthidae page) causes the young squid to resemble certain siphonophores suggesting protective mimicry.

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Figures. Lateral views, insitu with natural orientation, apparently of P. oligobessa, taken by a remotely operated vehicle (ROV) off California. Left image © MBARI 2001. Right image © MBARI 2011.

Nomenclature

This species was originally described as Valbyteuthis oligobessa. Valbyteuthis is now placed in the synonomy of Planctoteuthis (Young, 1991).

Life history

The holotype is a gravid, mated female with mature ovarian eggs of 1.5 mm in diameter. Spermatangia were found within the ovary. Fertilization, apparently, is internal.

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Figure. These two images of, presumably, P. oligobessa are apparently much older than those shown previously judging by the heavy pigmentation. Both images could be of adult squid, especially the bottom one with the damaged tail. Both images: © 2011 MBARI.

Distribution

Vertical distribution

The vertical distribution of P. oligobessa off southern California extends from 700 - 1200m (the maximum depth of the trawling program). The highest capture rate occurred in the 1100-1200 m zone and this species was one of the deepest living cephalopods taken in this program (Roper and Young, 1975). There is no difference between daytime and nighttime distributions.

Geographical distribution

P. oligobessa has been described only from the waters off southern California and northern Baja California; Nesis (1982/87) indicates that the distribution extends to Indonesian waters.

References

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