Planctoteuthis oligobessa

Planctoteuthis oligobessa Young 1972

Richard E. Young and Clyde F. E. Roper
The holotype is deposited in the Santa Barbara Museum of Natural History, Santa Barbara, California.
     
    Containing group: Planctoteuthis
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    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:

    A Planctoteuthis with ...
    • 2-4 suckers on each arm IV.
    • fin length 1/4 - 1/3 of ML.
    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.
        Click on an image to view larger version & data in a new window

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

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

        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
       ParatypeParatypeHolotype
      Sex----Female
      Mantle length343476
      Mantle width111128
      Fin length7814
      Fin width12----
      Length, arm I121119
      Length, arm II151527
      Length, arm III181629
      Length, arm IV464130
      Club length*64--
      Arm IV sucker count (left / right)3 / --3 / 22 / 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.

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

    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.

    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.
    Paralarval stages for P. oligobessa are unknown. 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.
    Click on an image to view larger version & data in a new window
    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.