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Illustration of the head of the Antarctic fish Trematomus bernacchii showing the 16 anatomical landmarks used for geometric morphometric analyses. The numbered landmarks correspond to: (1) anterior-most point of the premaxilla; (2) posteriomedial end of the operculum; (3) origin of the epiaxial musculature; (4) depression corresponding to the insertion of the sternohyoid muscle; (5) anterior end of the anteroposterior orbital axis; (6) posterior end of the anteroposterior orbital axis; (7) dorsal end of the dorsoventral orbital axis; (8) ventral end of the dorsoventral orbital axis; (9) posterodorsal end of the maxilla; (10) posteroventral end of the maxilla; (11) anterodorsal end of the premaxilla; (12) anteroventral end of the lower jaw; (13) posterodorsal end of the adductor muscle; (14) posteroventral end of the adductor muscle; (15) anteroventral end of the adductor muscle; and (16) anterodorsal end of the adductor muscle. The landmarks define key skeletal, muscular, and orbital reference points used to quantify head shape variation among Antarctic fish species.