Abralia Gray 1849

Introduction

Species of Abralia are small squid some of which are associated with shallow bottoms on steep slopes and as such are members of the mesopelagic-boundary fauna.

Brief diagnosis: 

An enoploteuthid ... 

• without large, black photophores at the tips of arms IV (see, however, A. astrolineata).
• with fins extending to posterior tip of tail.
  
  

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  Figure. Abralia trigonura. Same squid as in title image. Note the slender extension of the fin to the tip of the tail. Photographed in situ by  Jeffrey Milisen

Characteristics

1. Arms
   1. Arm suckers present distally on Arms IV.
      
      
2. Tentacles
   1. Manus of club with one series of hooks; two series of suckers.
      
      

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      Figure. Oral view of the tentacular club of Abralia veranyi, female, 38 mm ML, North Atlantic. Photograph by R. Young.
      

3. Buccal crown
   1. Typical chromatophores on oral surfaces of buccal crown.
      
      
4. Photophores
   1. Enlarged photophores on tips of arms IV generally absent; if present, not covered by black chromatophores (exception in A. astrolineata).
   2. Five to twelve photophores on each eye.
   3. Complex photophores of integument without red-colored filters.
5. Spermatangia receptacles
   1. Located under dorsal collar, in median pocket at posterior end of nuchal cartilage, or under gladius between stellate ganglia.
      

Comments

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Figure. Ventral view of arm IV integumental photophores of A. trigonura, off Hawaii. Photograph by R. Young.

In life, the integumental photophores have a characteristic appearance. The photo shows the three types of integumental photophores. A "lensed" photophore (white arrow) has a blue color and white ring. A "simple" photophore (black arraow) is small and violet-colored. The remaining are "complex" photophores and have a central green color and small "satellite" green-color points. Often complex photophores will appear blue rather than green depending on their physiological state (see Young and Arnold, 1982). The black dots are chromatophores.

The structure of a complex photophore can be seen here. 

Classification

Species of Abralia are generally placed into six subgenera but these may not all be natural groups. The following table (modified from Tsuchiya and Okutani, 1988, and Tsuchiya, 1991) shows the primary taxonomic features of each group.

References

Nesis, K. N. 1982. 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.

Tsuchiya, K. 1991. Abralia fasciolata, a new species of enoploteuthid squid from the western Indian Ocean (Cephalopoda: Oegopsida). Bulletin of the National Science Museum, (series A) 17(2):69-79, 16 figures.

Tsuchiya, K. and T. Okutani. 1988. Subgenera of Enoploteuthis, Abralia and Abraliopsis of the squid family Enoploteuthidae (Cephalopoda, Oegopsida). Bulletin of the National Science Museum, Tokyo (series A) 14: 119-136.

Young, R. E. and J. M. Arnold. 1982. The functional morphology of a ventral photophore from the mesopelagic squid, Abralia trigonura. Malacologia 23: 135-183.

Young, R. E., L. A. Burgess, C. F. E. Roper, M. J. Sweeney and S. J. Stephen. 1998. Classification of the Enoploteuthidae, Pyroteuthidae and Ancistrocheiridae. Smithsonian Contr. to Zoology, No. 586.