Illex Steenstrup 1880

Introduction

This subfamily, as currently recognized, contains only the genus Illex. These are commercially important species found in neritic waters of the North and South Atlantic (Roper et al., 1998). The number of species in the North Atlantic has been controversial, with the validity of I. oxygonius repeatedly questioned. Carlini et al. (2006) used molecular methods to confirm that three species are present in the North Atlantic. Since I. oxygonius  occupies waters where the distributions of I. illecebrosus and I. coindetii overlap, it could represent a hybrid of these species (Roper, et al., 1998).  Morphological identification of specimens, even mature males, can be quite difficult since all four species exhibit considerable intraspecific morphological variability; no single character will allow consistent identification of species (Roper, et al., 1998).

Brief diagnosis:

Ommastrephids with ... 

• suckers in eight series on tentacular club dactylus. 

Characteristics

1. Arms
   1. Either right or left ventral arm hectocotylized.
   2. Distal portion of hectocotylus without protective membranes.
      
   

   Click on an image to view larger version & data in a new window

   
   

   

   Click on an image to view larger version & data in a new window

   
   

   Figure. Oral views of the distal region of the hectocotylus of Illex oxygonius. Top - Photograph by M. Vecchione. Bottom - Drawing from Roeleveld (1988). v - Ventral side.
   
2. Tentacles
   1. Large, medial club suckers with smooth or bluntly crenulated inner rings.
   2. Dactylus of tentacular club with suckers in eight series.
   3. Carpal locking-apparatus absent.
      
   

   Click on an image to view larger version & data in a new window

   
   

   Figure. Oral view of the dactylus of the tentacular club of Illex sp. Photograph by M. Vecchione.
3. Head
   1. Funnel groove without foveola or side pockets.
      
      
4. Funnel
   1. Funnel/mantle locking apparatus with simple inverted T-shape. 
      
      

      Click on an image to view larger version & data in a new window

      
      

      Figure. Funnel (left) and mantle (right) components of the funnel/mantle locking apparatus of Illex illecebrosus, stained with methylene blue stain. Photographs by R. Young.

5. Photophores
   1. Photophores absent.
      
      
6. Comparison of species

   	I. illecebrosus	I. coindetii	I. argentinus	I. oxygonius
   Hectocotylus midsection with papillose, fringed flaps	No	Yes	No	No
   Largest distal medial manal club-sucker dentition	Smooth	7-8 broad, flat teeth	Smooth or few notches	Smooth
   Longest arm (arm II or III)	~ 50% ML	~ 60% ML	~ 70% ML	~ 55% ML
   Length distal portion of hectocotylus	~ 22 % ML	~ 25 % ML	~ 50 % ML	~ 29 % ML
   Length proximal bare portion of hectocotylus	~ 10 % ML	~ 13 % ML	~ 10 % ML	~ 4 % ML

Behavior

All species of Illex appear to congregrate, at least on occasion, near the ocean floor and spend time sitting on the ocean floor.

Click on an image to view larger version & data in a new window

Figure. Illex illecebrosus. Left - squid swimming near the ocean floor at 780 m depth, off Northeastern coast of USA. Right - Squid sitting on the ocean floor at xxx m, in same general region.

Distribution

Species of Illex are found only in the Atlantic Ocean -- Western Atlantic Ocean from equator to Iceland and from southern Brazil to Patagonia, and eastern Atlantic from 20°S to 60°N, including Mediterranean Sea. These species are generally confined to continental shelf and slope areas, or nearby oceanic waters, perhaps because of their habit of sitting on the bottom at depths of up to 1000 m.

Click on an image to view larger version & data in a new window

Figure. Distribution chart of all four species of Illex; modified from Roper et al. (1998).

Other Names for Illex Steenstrup 1880

• Illicinae Posselt 1891

References

Carlini, D.B., L.K. Kunkle, and M. Vecchione. 2006. A molecular systematic evaluation of the squid genus Illex (Cephalopoda: Ommastrephidae) in the North Atlantic Ocean and Mediterranean Sea. Molec. Phylog. Evol. 41:496-502.

Roper, C.F.E., C. C. Lu, and M. Vecchione. 1998. Systematics and distribution of Illex species; a revision (Cephalopoda, Ommastrephidae). In: Voss, N.A., et al. (eds.) Systematics and Biogeography of Cephalopods. Smithson. Contr. Zool. 586:405-423.