Onykia robsoni (Adam, 1962)

Introduction

Adults of O. robsoni reach a length of 470 mm ML. This species apparently has the broadest distribution of any member of the genus.

Diagnosis

An Onykia ...

• with sagittate fins (fins drawn-out posteriorly).
• with warts rather than ridges on skin.
  

Characteristics

1. Tentacles
   1. Club with 13-16 pairs of hooks.

      Scanning electron micrographs of the hooks can be found here.

2. Mantle
   1. Covered with fleshy, irregular warts.
      image info

      Figure. Dorsal view of mantle warts of O. robsoni, holotype. Photograph from Adam, 1962.

3. Fins
   1. Sagittate shape.
   2. Length 53-62% of ML at 156-370 mm ML.
   3. Width 51-70% of ML at 156-370 mm ML.


4. Gladius
   1. Rostrum ventral length 23-36% of GL; triangular in cross-section.

Comments

The above data is from Kubodera et al., 1998. This species is very similar to O. robusta in the shape of the fins but is separated by the structure of the skin (i.e., warts vs ridges), and the fewer pairs of club hooks (13-16 vs 16-18).

Additional features of the description are found here.

Nomenclature

Onykia aequatorialis (Thiele, 1920) was described from the equatorial Atlantic at 18°07'W. Kubodera, et al., 1998, examined a spent female of O. robsoni from Bermuda that was very similar to O. aequatorialis which caused them to question the validity of the latter. Since the holotype has been lost and there are no distinguishing features in the type description, they designated O. aequatorialis a nomen dubium.

Distribution

The type locality is off Angola at 16° 36'S, 11°20'E. This species occurs north of the southern subtropical convergence, off southwestern Australia, New Zealand and southern Africa and it is indistinguishable from specimens taken from the Gulf of Mexico and off Bermuda in the North Atlantic (Kubodera, et al., 1998). It is also reported off the southwestern coast of South America.

References

Adam, W. 1962. Cephalopodes de l’Archipel du Cap-Vert, de l’Angola et du Mozambique. Memorias da Junta de Investigacoes do Ultramar, series 2, 33: 9-64.

T. Kubodera, U. Piatkowski, T. Okutani and M.R. Clarke. 1998. Taxonomy and Zoogeography of the Family Onychoteuthidae (Cephalopoda: Oegopsida). Smithsonian Contributions to Zoology, No. 586: 277-291.