Length to 25 mm (females), to 19 mm (males). In females (Phronima solitaria 1), pleon and urosoma (including UR) combined 0.90±0.03 times as long as head and pleon combined; pleonite I 0.66±0.05 times as long as pereonite VII. Carpal process of P V strong, curved (Phronima solitaria 3); carpal tubercle strong, narrow, single (or with weak and poorly separated anterior tooth), with 7-9 tooth-like projections; ventral tip of carpal tubercle protruding downward beyond posterior ("ventral") margin of ART 6, almost reaching level of tip of carpal process. ART 6 more or less longer than palmar margin of ART 5, metacarpal tubercle present but weak. Rami subequal in all UR.
In males (Phronima solitaria 2), pleon and urosoma (including UR) combined slightly longer than head and pleon combined; pleonite I slightly shorter than pereonite VII. Animals look like males of Phronima sedentaria, but have long, well-developed ANT II (slightly shorter than ANT I), and moderately shorter carpal process and ART 6 of P V (but ART 6 still longer than palmar margin of ART 5).