Mesonychoteuthis hamiltoni Robson, 1925

Introduction

Mesonychoteuthis hamiltoni is the largest of all cranchiid species with adults reaching over 2 m in mantle length (Nesis, 1982). It is a circumpolar Antarctic species with young found north to the subtropical convergence (Nesis, 1982).

Diagnosis

A taoniin ...

• with hooks on the arms and tentacle clubs.

Characteristics

1. Arms
   1. Hooks present on arms.
      

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      Figure. Oral view of half of the arm crown (arms I-IV, arm I at top) of a juvenile M. hamiltoni, 86 mm ML. Drawing from Voss (1980), p. 395.

      

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      Figure. Dorsal view of the brachial crown of a large M. hamiltoni. Photograph by Martin Collins.

2. Tentacles
   1. Tentacular club with hooks.
   2. Diagonally set pairs of suckers and pads on distal 2/3 of tentacular stalk.
   

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   Figure. Oral view of the tentacular club of a large M. hamiltoni. Note the very small marginal suckers. Photograph by Martin Collins.
3. Funnel
   1. Funnel valve absent.
   2. Funnel organ: Dorsal pad with three papillae.
      
      
4. Mantle
   1. Tubercles absent in adults, present in paralarvae and juveniles.
      
      
5. Fins
   1. Fins ovate, without anterior lobes.
   2. Fins terminal.
      
      
6. Photophores
   1. Two ocular photophores: crescent-shaped medial photophore and small, oblong lateral photophore within concavity of first.
   2. Arm tip photophores probably absent.

Comments

This is the only cranchiid that has hooks on the arms. Characteristics are from Voss (1980).

Life History

The young stages were described by McSweeny (1970). Hooks first appear on the arms at about 45 mm ML.

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Figure. Top - Dorsal view of an advanced paralarva of M. hamiltoni, 23 mm ML. Bottom - Ventral view of a juvenile of M. hamiltoni, 86 mm ML. Drawings from Voss (1980, p. 395, fig. 10 c, b).

Distribution

M. hamiltoni is known only from Antarctic waters. A map of its distribution can be found here.

References

Nesis, K. N. 1982/87. Abridged key to the cephalopod mollusks of the world's ocean. 385+ii pp. Light and Food Industry Publishing House, Moscow. (In Russian.). Translated into English by B. S. Levitov, ed. by L. A. Burgess (1987), Cephalopods of the world. T. F. H. Publications, Neptune City, NJ, 351pp.

McSweeny, E. S. 1970. Description of the juvenile form of the Antarctic squid Mesonychoteuthis hamiltoni Robson. Malacologia, 10: 323-332.

Voss, N. A. 1980. A generic revision of the Cranchiidae (Cephalopoda; Oegopsida). Bull. Mar. Sci., 30: 365-412.