Guérin-Méneville, 1836
Length to 24 mm (females), to 13 mm (males). In females (Phronima atlantica 1), pleon and urosoma (including UR) combined 0.92±0.02 times as long as head and pleon combined; pleonite I 0.70±0.04 times as long as pereonite VII. Carpal process of P V moderate (Phronima atlantica 3), protruding only slightly beyond posterior ("ventral") margin of ART 6; carpal tubercle bifid, weaker than carpal process, not protruding beyond posterior margin of ART 6, with 4-5 tooth-like projections on posterior margin; ART 6 longer than palmar margin of ART 5, metacarpal tubercle indistinct. UR I with exopodite slightly shorter than endopodite; UR II with exopodite longer than endopodite; UR III with subequal rami.
In males (Phronima atlantica 2), pleon and urosoma (including UR) combined 1.14±0.04 times as long as head and pleon combined; pleonite I 0.9 5±0.04 times as long as pereonite VII. ANT II well-developed, usually longer than ANT I, flagellum 11-12 articulated. Carpal process of P V moderately developed (Phronima atlantica 4), protruding only slightly beyond posterior ("ventral") margin of ART 6; carpal tubercle shorter than carpal process, bifid, posterior part with 4-5 tooth-like projections; ART 6 moderately longer than palmar margin of ART 5. Exopodite of UR II slightly longer than endopodite, in UR I and III both rami subequal.