Sars, 1902
Females
Body elongate. Ce and Pd1 separate, Pd4 and 5 fused, posterolateral corners of Pr usually rounded, expanded in Gaussia; Pd1 with dark-pigmented spot on one side in Pleuromamma. Ur of 3 somites, CR often asymmetrical with up to 6 setae; genital apparatus comprising a common genital aperture located medially on ventral surface of Gns; copulatory pore contained within median genital aperture. R with paired filaments. A1 23-24-segmented; segments 1 and 2 fused, segments 3 to 7 separate, segments 8 and 9 fused, segments 10-22 separate, apical segment double. A2 with Coxa and Basis separate with 1 and 2 setae respectively; Enp 2-segmented, bilobed distal segment with 1-2, 8-9+6-7 setae; Exp 7-segmented with 1, 2, 1, 1, 1, 1, 4 setae respectively. Md with well-developed gnathobase, palp Basis with 4 setae; Enp 2-segmented with 4 and 10 setae respectively; Exp 5-segmented with 1, 1, 1, 1, 2 setae respectively. Mx1 Li1 with about 15 spines and setae, Li2-4 with 4-5, 4, 5-7 setae; Enp 2-segmented with 6, 9-12 setae; Exp with 11 setae; Le1 and 2 with 9 and 1 setae respectively. Mx2 Li1-5 with 5 (9 in P. xiphias), 3, 3, 3, 4 setae respectively; Enp 4-segmented with 3-4, 3, 2, 2 setae, or reduced. Mxp 7-segmented, Coxa with 1, 2, 4, 4 setae; Basis with 3 setae plus 2 setae on the incorporated Enp segment 1; free Enp 5-segmented with 4, 4, 3, 3, 4 setae respectively. P1-4 with both rami 3-segmented; Exp of P2-4 very large and flat, outer margin spines small. P1 Basis inner seta situated on its anterior surface and passing across face of Enp segment 1. Enp segment 1 of P2 typically incised and ornamented with 1 or more hook-like spinous processes; Enp typically small, cylindrical.
Spine and seta formula typically as follows but sometimes reduced: Spine and seta Metridinidae.
P5 uniramous, very small, symmetrical 2-4-segmented, Coxa and intercoxal sclerite fused; Basis and Exp segment 1 usually with outer seta and spine respectively; Exp segment 2 with 2-4 setae, terminal Exp segments may be fused.
Males
Ur of 5 somites, sometimes strongly asymmetrical, single genital aperture located ventrolaterally at posterior margin of Gns, usually on right side, sometimes on left. A1 usually prehensile on left side only, occasionally on right side only. Insert Mouthparts similar to those of female. P5 asymmetrical, attached to plate formed from fusion of Coxa and intercoxal sclerite; right leg comprising Basis with an outer seta and ?2-3-segmented Exp, Exp segment 2 with an inner spinous process in some genera, Exp segment 3 with 1 or 2 minute distal setae; left leg comprising Basis with outer seta and 2- or 3-segment Exp: Exp segment 1 bearing curved inner process, distal segment swollen, often curved or claw-like.
This family contains three genera, all of which occur in the South Atlantic:
Genus Gaussia Wolfenden, 1905
Genus Metridia Boeck, 1864
Genus Pleuromamma Giesbrecht, 1898