(Fig. 2 G; Table 3)
Material examined. 2 specimens (34.0– 46.1 mm SL): MNRJ 30348, 1(34.0 mm), AG 2-14; MNRJ 30359, 1(46.1 mm), AG 2-13.2.
Diagnosis. Sternoptyx pseudodiaphana can be differentiated from its congeners by the following combination of characters: SAN photophore positioned at approximately 3 or less times in trunk depth, not more than 3.5 times in sub-adults; trunk depth subequal to trunk length; vertebrae 30–32, rarely 29; dorsal-fin rays 9–13, usually less than 12; pectoral-fin ray bases pigmented in juveniles; dorsal-fin base usually smaller than dorsal-blade base, occasionally equal.
Meristic description. Fin rays: D 11–12; A 14; P 1 10; P 2 5. Gill rakers: 7–8 (4–5 + 1 + 2–3). Photophores: BR 5; I 5; AB 10; PAN 3; AN 3; SC 4.
Distribution. Widely distributed in Southern Ocean and associated boundary currents in Southern Hemisphere, between 20 ° and 50 °S.
Remarks. These specimens represent the first records of S. pseudodiaphana in the western South Atlantic.