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Containing group: Taonius

Introduction

Taonius belone is the tropical Indo-Pacific congener of the temperate/boreal Pacific T. borealis. Nesis (1972) originally described two subspecies under the name T. borealis : T. b. borealis and T. b. pacifica. The latter was based largely on Sasaki's 1929 description of "T. pavo" much of which is reproduced below. However, Chun (1906, 1910) had described a juvenile species of the genus (T. belone) from the Indian Ocean and Nesis (1982/87) placed T. b. pacifica within the synonymy of T. belone. N. Voss (see Nomenclature under the Taonius genus page) is very familiar with this genus and supports this synonomy.

Brief diagnosis:

A Taonius with ...

• Largest club sucker with two primary hook-like tooth and no secondary hook-like teeth.
• Large club suckers of marginal series of manus laterally compressed.
  

 

Characteristics

1. Arms
   1. Arms short; formula: 3>2=4>1.
      
   2. Protective membranes narrow except their proximal part, which are wide and connected together into an internal umbrella.
   3. Arm suckers biserial throughout, crowded distally; suckers number 21 pairs or more on each arm. Largest suckers about 8th pair.
   4. Larger suckers with 20-30, broad, closely set teeth around entire margin of ring; distal suckers with only 6-8 teeth; proximal suckers with teeth united appearing smooth except for few distal undulations.
   

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   Figure. Oral views of arm suckers of T. belone. Left - Arm III, sucker 20, 119 mm ML. Drawing from Voss (1963). Middle - Large arm sucker, 330 mm ML. Right - Distal arm sucker, 330 mm ML. Latter two drawings from Sasaki (1929).
2. Tentacles
   1. Largest two (?) suckers of medial two series of club manus with one or two enlarged, hook-like teeth; smaller secondary teeth absent.
   2. Other enlarged suckers of medial series of club manus with two largest hook-like teeth more nearly equal in size; 4-5 smaller secondary teeth present.
      
   3. Suckers of marginal series of manus  laterally compressed, each with two elongate, incurved teeth on distal and pointed teeth on lateral margin of sucker ring.
   4. Tentacular stalk with two series of locking suckers on distal 2/3 to 3/4 of stalk. Indistinct carpal cluster at base of manus.
   

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   Figure. Oral view of the tentacular club of T. belone, 330 mm ML, showing enlargement of some suckers. Drawing from Sasaki (1929).
   

   

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   Figure. Oral views of club sucker rings of T. belone, Phillipine Islands. Drawing from Voss (1963).
3. Head
   
   1. Beaks: Descriptions can be found here: Lower beak; upper beak.
      
      
4. Mantle
   1. At funnel-mantle fusion, tubercules absent .
   2. Mantle skin smooth.
      
      
5. Fins
   1. Fins elongate, lanceolate and subterminal; each fin at anterior insertion broadly separated from each other; fin length 44% of ML.
   2. Gladius extends beyond fins as axis of tail .
      

Comments

The above characteristics are taken from Sasaki, 1929 and Voss, 1963.

Life History

Paralarvae of T. belone from Hawaiian waters have been identified. they are distinctive among cranchiid paralarvae from these waters in the near lack of chromatophores.

Young (1975) found that the structure of the eyes changed with the vertical distribution of this species as in Sandalops melancholicus. Although data were few, he found paralarvae with stalked, laterally compressed eyes, in the upper 400 m; juveniles from 50 to 140 mm ML were captured between 500 and 700 m with most taken between 600 and 650 m. At depths greater than 700 m the squid had hemispherical eyes.

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Figure. Ventral-oblique (left) and ventral (right) views of a tubular eye of a juvenile T. belone, off Hawaii. Photograph by R. Young.

The laterally compressed eyes of paralarvae will reduce the size of a shadow cast by the opaque eyeballs under the highly directional downwelling daylight to aid in camouflage. In deeper waters where the intensity of downwelling daylight is reduced the upward looking tubular eye is more easily camouflaged with silvery mirrors on the sides and a photophore on the underside of the eye to match the weak downwelling light and, thereby, eliminate the eye shadow (= counterillumination). In deeper water yet, darkness allows the eye to assume a more normal shape that allows a broader visual field (Young, 1975).

Distribution

Geographical distribution

Type locality: Indian Ocean at 10°8'S, 97°14'E.

Found off southern Japan, Philippine Islands, Hawaiiiian Islands, central equatorial Pacific and, presumably throughout the tropical and subtropical Indo-Pacific, but details are poorly known. 

Vertical distribution

Off Hawaii T. belone appears to exhibit ontogenetic descent and not to undergo diel vertical migration (Young, 1975). 

Other Names for Taonius belone (Chun, 1906)

• Taonius pacifica pacifica Nesis, 1972
• Toxeuma belone Chun 1906

References

Sasaki, M. 1929. A Monograph of the Dibranchiate Cephalopods of the Japanese and Adjacent Waters. Journal of the College of Agriculture, Hokkaido Imperial University, 20(supplement):357 pages.

Voss, G. L. 1963. Cephalopoda of the Philippine Islands. Bull. U. S. Nat. Mus., 234: 1-180.