Mantle cylindrical in the anterior half, conical in the posterior half, its width in adults 3-6 times less than ML. No tail. Mid-dorsal mantle projection tongue-like, noticeable even in larvae. Fins transversely tongue-like in larvae, oval in juveniles, elongate diamond-shaped in adults, fin length equal to or longer than width. Arm length in adults >25% ML. Central club suckers much larger than marginal ones. Buccal membrane with small suckers. Lateral sides of gladius bent arch-like, without marginal ribs. No photophore. Egg size: length 2.3-2.7, width 1.8-2.2 mm.
Newborn larvae (ML approx. 2.2 mm) with 9 red chromatophores dorsally on mantle, 4 on dorsal side of head and 2 patches ("cheek patches") of 4 chromatophores each on ventral side of head. ML in adults up to 50 cm. Two subspecies; only Loligo vulgaris reynaudii d'Orbigny, 1845 recorded from the SE Atlantic.
Three related species have been mentioned for the SW Atlantic: Loligo (or Amerigo according to some authors) sanpaulensis Brakoniecki, 1984 (= L. brasiliensis sensu Castellanos and Menni, 1969, L. emmakina Gray, 1849); L. (or Amerigo) patagonica Smith, 1881 (= L. gahi Brakoniecki, 1984, partim, ?non d'Orbigny, 1835), the deepest, approx. 80-800 m, and coldest-living loliginid; and Doryteuthis plei (Blainville, 1823). Larvae of D. plei (McConathy et al., 1980), L. sanpaulensis (Leta, 1987a), and L. patagonica (Rodhouse et al., 1992) are hardly distinguishable from those of Loligo (Sweeney et al., 1992; Vecchione and Lipinski, 1995).