Deliberations on the External Morphology and Modification of the Labial Segments in the Nepomorpha (Heteroptera: Insecta) with Notes on the Phylogenetic Characteristics
Shapes of the labial segments of the Helotrephidae. (a)–(g) Hydrotrephes balnearius. (a) Dorsal view of the labium, the shape and size of the IV segment (this segment is longer than the remaining three), (b) the shape of the second segment (a triangular plate with evidently raised nodules in the distal part of the triangular plate) and the tubular third segment, (c) dorsal view of the labium, the first segment (I) is a narrow strap with the open stylet groove (gr), the second segment is divided into the triangular plate (tp) and the concave plate (cp), the triangular plate features pairs of nodules (no), the tubular III segment, the articulation between the second and third segments (cd), the IV segment has a conical shape, the stylet groove is closed in these segments, (d) ventral view (V) of the labium, on the distal edge of the first segment (I) and the proximal edge of the fourth segment there is the midventral condyle (cv), (e) the I and II segments magnified, (f) the oval apical plate can be observed, and (g) lateral view of all segments (the fourth segment is the longest). Lr: labrum, stb: stylet bundle.
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