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Neotype - Mature male, 199 mm ML, National Museum of Natural History, Smithsonian Institution, USNM 727456.

Containing group: Illicinae

Introduction

I. illecebrosus. the northern shortfin squid, is probably the most abundant cephalopod in the western North Atlantic, and is the target of an intensive fishery off northeastern North America. It is also very important as both predator and prey in the continental shelf and slope ecosystems of that area.

Characteristics

1. Arms
   1. Hectocotylus (either left or right arm IV)
      

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      1. Hectocotylus shorter than or equal to its opposite arm in length, always equal in thickness.
         
      2. Distal portion (HA3) of arm IV 13%-30% of total arm length with weakly developed papillae and lamellae.
      3. Basal portion (HAb) short, about 6% of total arm length.
      4. Proximal portion (HA1) with 7 to 8 pairs of normal suckers increasing in size distally.
      5. Middle portion (HA2) with suckers about 3/4 diameter of proximal suckers; oral surface of arm not expanded; sucker rows not abnormally separated; very slight constriction between HA1 and HA2; trabeculae not modified as fringed lobes.
         
         

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         Figure. Generalized diagram of an Illex hectocotylus defining the terminology used. Drawing modified from Roper, et al. (1998).
         

2. Tentacles
   
   1. Largest distal medial manal sucker-rings smooth, without crenulations or notches.
      
      

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      Figure. Oral view of the tentacular club of I. illecebrosus. Drawing from Roper, et al., (1984)
      

3. Head
   1. Head-width index low, 16.3-17.0.
      
   2. Beaks: Descriptions can be found here: Lower beak; upper beak.
      
      
4. Fins
   1. Fin angle usually 45° (40°-50°), never > 50°.
      
      
5. Reproductive structures
   1. Spermatophore: "Spermatophore cone at oral end of cement body, a low, right-isosceles triangle with rounded corners in outline; oral tube long, narrow; aboral neck long, narrow" (Roper, et al., 1998).

Life History

I. illecebrosus inhabits inshore waters in summer and retreats to deeper, offshore waters of the continental shelf and slope in autumn and winter. It occurs in temperatures of 0° to 15°C, optimum 7° to 13°C, so it is restricted to northern waters. Spawning grounds and season are unknown, but recent data indicate a late autumn-early winter spawning in offshore slope water near the inshore edge of the Gulf Stream. An inshore summer migration is associated with intensive feeding, primarily on small fishes and euphausiids.

Distribution

Type locality - Northwest Atlantic near the Isles of Shoals, New Hampshire, United States, at approximately 43°N, 70°30'W.

Geographical distribution - Western North Atlantic from 66°N, and Baffin Island, to about 29°N in the Straits of Florida. Records apparently of I. illecebrosus exist from Iceland, southern Greenland and the Mid-Atlantic Ridge but these may be strays from the normal habitat (Roper et al., 1998).

Vertical distribution -  I. illecebrosus is primarily a neritic species of the continental shelf and upper slope. Its vertical range is extensive depending on size, season, and time of day. It has been caught from the surface to about 1 000 m depth; but tends to congregate on or near the bottom during the day and disperse into the water column at night.