Planctoteuthis

1. 1. Arms
      1. Subequal in length in adults; arms IV much the longest in young.
      2. Arms IV with relatively few suckers in the proximal 1/3 of arm or less, remainder of arm without suckers. Suckers usually aligned in virtually single series.The reason for the peculiar structure of arms IV is unknown. The following images provides clues to this problem. These photographs show the bases of arms IV, presumably the sucker-bearing region, locked together. The tentacles (arrows in 1st and 3rd photos, in the 2nd photo, the tentacles have curlicue ends) emerge, adjacent to one another, from the joined arms IV . Apparently the proximal, sucker-bearing region of arms IV, and their lateral membranes, form a single tentacular sheath for holding both tentacles. The value of this arrangement and the function of the bare, distal arms IV is unknown. Also, the coiling of the tentacles suggests that they are not strongly retractile.

Figure. Planctoteuthis danae, Gulf of California, in situ ROV photographs. Left, middle - Slightly different anterodorsal views of the same squid, 1206 m depth. Right - Side view of a different, probably larger squid, ? depth. This species has 12-13 suckers on the proximal third of arms IV. All three photographs © 2013 MBARI.

1. Tentacles
   1. Club small, compact.
   2. Club keel absent in some species.
   3. Club without carpal locking apparatus.
   4. Low protective membranes/ridges along both boarders of club.
   5. Not divided into proximal and distal regions by protective membranes.
      

      Figure. Oral view of tentacular club of Planctoteuthis lippula, Hawaiian waters, 35 mm ML. Photograph by R. Young.
2. Head
   1. Head with elongate neck and brachial pillar.
   2. Eyes commonly project ventrally from head.
      

      Figure. Lateral view of head of Planctoteuthis lippula, Hawaiian waters, 35 mm ML. Photograph by R. Young.
3. Funnel
   1. Funnel valve absent.
   2. Funnel locking apparatus oval with posterior bump (antitragus) (see Comments).
   3. The exact form of the antitragus in the funnel locking-apparatus is often a species-specific feature. Unfortunately this structure is difficult to see and lighting and angle of view can often give different apparent results. The character must be used cautiously. Compare the locking apparatuses of the following species:
      

      Figure. Funnel component of the funnel/mantle locking apparatus of various species of Planctoteuthis. A - P. danae. B - P. levimana, 60 mm ML. C - P. lippula, 55 mm ML. D - P. oligobessa. Photographs by R. Young.
4. Photophores
   1. Absent.
5. Tail
   1. Tail present (usually lost during capture) with appendages. Appendages undescribed.

Comments

Figure. Funnel component of the funnel/mantle locking apparatus of various species of Planctoteuthis. A - P. danae. B - P. levimana, 60 mm ML. C - P. lippula, 55 mm ML. D - P. oligobessa. Photographs by R. Young.