Figure 5.

General model of the labium focusing on the character of the segment in the Belostomatidae and Helotrephidae. (a) dorsal side of the labial segments in Hydrocyrius colombiae (Belostomatidae), (b) ventral side of the labial segments in Hydrocyrius colombiae (Belostomatidae), (c) dorsal side of the labial segment in Hydrotrephes balnearius (Helotrephidae), (d) detailed shape of the I and II segments, dorsal view, (e) ventral side of the labial segments. ap: apical plate, cd: dorsal condyle, cv: midventral condyle, gr (o): open stylet groove, gr: closed stylet groove, gr (no): stylet groove has no definite lips, is: intercalary sclerites, lo: lateral lobe of apex, mb: intersegmental membrane, no: nodule of triangular plate, tp: triangular plate, I, II, III, IV numbers of the labial segments.