Taonius Steenstrup, 1861

Introduction

Species of Taonius are large squids (up to 660 mm ML) with long, slender terminal fins (as seen in the video still frame below) and hooklike teeth on largest club suckers. They are found circumglobally in the midwaters of the open ocean. An AVI/MPEG format video clip of this animal is available at Cephalopods in Action.

Brief diagnosis:

A taoniin ...

• with large, claw-like suckers in the medial two series on the club manus.
• with long, lanceolate, terminal fins.

Characteristics

1. Tentacles
   1. Tentacular clubs with enlarged suckers that bear one or two large, central, hook-like teeth.*
   2. Distal 2/3 of tentacular stalk with two series of suckers and pads.
   3. Terminal pad on club with 2-3 suckers separated from dactylus suckers by narrow "neck."
      
   

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   Figure. Oral view of the tentacular club of T. pavo, 198 mm ML. Drawing from Voss (1980, p. 391, fig. 8e).

2. Head
   1. Eyes large, bulge from head, anteriorly oriented.
      
      
3. Funnel
   1. Funnel valve absent.
   2. Funnel organ: Dorsal pad with three round, fat papillae.
      
      
4. Mantle
   1. Tubercles absent at funnel-mantle fusion (single tubercle may be present in young).
      
      
5. Fins
   1. Terminal, lanceolate, very long and narrow; anterior insertion on gladius. However, the photograph below suggests that in T. borealis, at least, the anterior end of the fin attaches to the side of the mantle.
      
      

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      Figure. Side view of T. borealis virtually motionless in the water at a depth of 1397 m. Note the position of the anterior tip of the fin. Insitu photograph © 2011 MBARI.
      



Figure. Ventral view of the eye of a subadult T. pavo, 539 mm ML, showing photophores. Drawing from Voss (1980, p. 391, fig. 8d).

6. Photophores
   1. Two ocular photophores: Medial photophore large, crescent-shaped; lateral photophore small, crescent-shaped within concavity of first.
   2. Arm tip photophores absent.

*Unique in family.

Comments

Characteristics are from Voss (1980).

Development of the hook-like teeth on the medial suckers of the manus is highly dependent of the size of the squid. In T. borealis the adult club is present at about 15 cm ML (Nesis, 1972).

Comparison of species

Nomenclature

Chun (1906) named Toxeuma belone from the Indian Ocean at 10°08'S, 97°14'E on the basis of a single specimen of 51 mm ML. Lane (1957) pointed out that the generic name Toxeuma was preoccupied and proposed the name Belonella belone. Nesis (1972) maintained a generic separation between Belonella  and Taonius based in part on his observation of the different consistency of the tissues (gelatinous in Taonius and leathery in Belonella). Belonella and Taonius  were synonymised by Voss (1980), even though some authors did not accept this action(e.g., Nesis, 1987, Okutani, 2005). The identity/validity of Chun's species, however, was long considered uncertain;  ongoing research (Voss, pers. comm.), supporting previously published data (Nesis, 1987, Voss, 1988, Voss et al., 1992b) and working hypotheses (Young and Mangold, 2008), strongly  indicate that T. belone should be synonymised with T. pacificus (the latter species name obtained by synonymising Belonella (pacifica pacifica, Nesis, 1972) with Taonius). Thus,  the new combination is derived, Taonius belone (Chun, 1906), the specific name belone having priority.

Life history

As in Sandalops, species of Taonius go through a stage while in upper mesopelagic depths, in which the stalked eye has a nearly tubular shape (Young, 1975). The bottom of the eye is covered by two large photophores, one of which is strongly bilobed.

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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.

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Figure. Dorsal view of a young T. pavo (left) and a dorsal view of the anterior end of this squid (right), taken off Florida from a submersible of the Harbor Branch Oceanographic Institution. The eyes are just beginning the transition to a hemispherical shape. Large photophores appear to cover he posterior surface of the eyes. Photographs taken by E. Widder/HBOI.

References

Joubin, L. 1900. Céphalopodes provenant des Campagnes de la Princesse-Alice (1891-1897). Résult. Camp. Scient. Monaco, 17: 1-35.

Lane, F. W. 1957. Kingdom of the Octopus. The Life History of the Cephalopoda. Jarrolds. 287 pp.

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.

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

Voss N. A., S. J. Stephen and Zh. Dong 1992. Family Cranchiidae Prosch, 1849. Smithson. Contr. Zool., 513: 187-210.

Young, R. E. 1975. Transitory eye shapes and the vertical distribution of two midwater squids. Pac. Sci. 29: 243-255.