Length to 15 mm (females), to 9 mm (males). In females (Phronima pacifica 1), pleon and urosoma (including UR) combined 0.89±0.05 times as long as head and pleon combined; pleonite I 0.71±0.03 times as long as pereonite VII. ART 4 of P V wider than long with strongly produced posterior margin. ART 5 of P V dilated, with proximal posterior corner produced, carpal tubercle with 4-5 tooth-like projections, bifid; carpal process protruding slightly beyond posterior ("ventral") margin of ART 6; ART 6 subequal in length to palmar margin of ART 5. Rami subequal in all UR.
In males (Phronima pacifica 2), pleon and urosoma (including UR) combined 1.16±0.07 times as long as head and pleon combined; pleonite I 0.94±0.07 times as long as pereonite VII. ANT II well-developed, about half as long as ANT I, flagellum 15-17 articulated. Posterior margin of ART 4 of P V very strongly produced, forming a semicircular arc, ART 4 wider than long; ART 5 also wider than long, proximal posterior corner produced, carpal process moderately developed, curved carpal tubercle with separate anterior tooth and 4 tooth-like projections, first somewhat isolated from rest, last two usually low (Phronima pacifica 3); ART 6 subequal to palmar margin of ART 5. Rami subequal in all UR, or exopodite slightly longer than endopodite in UR II.