Mantle narrow, its width 1/4-1/6 ML. Fin heart- or narrowly diamond-shaped, width 45-60% ML. Eight transverse rows of small suckers at club end. Teeth of large tentacular suckers approximately equal in size. Carpal group of tentacular suckers short, compact, fixing apparatus without knobs. Funnel pit without foveola and side pockets. No photophores. ML up to 40 cm.
Larvae: proboscis short, usually 1/4-1/2, rarely to 3/4 ML, usually shorter than arms. All suckers on the proboscis tip equal in size. Proboscis division beginning at ML approx. 4-5 mm, finished at 6-8 mm. Arms of 3rd pair beginning to develop (first suckers appear) at ML approx. 1.5 mm, of 4th pair at 3.5 mm. Tentacular ends in juveniles from ML 10-15 mm with more than 4 rows of suckers.
Two species in the South Atlantic: Illex argentinus (Castellanos, 1960) distributed in the SW Atlantic, a very common and important commercial species; and a close species Illex coindetii (Vérany, 1837), distributed on both sides of tropical Atlantic. Both inhabit near-bottom layers on the shelf and slope and pelagic layers over the shelf, slope, and "nearshore abyssal" areas. Larvae and juveniles seem indistinguishable. A third species, Illex illecebrosus (LeSueur, 1821), also an important commercial squid, inhabits the N Atlantic.