Fig. 8

Lines and curves as diagnostic characters. A, B Shell outline differs between Cerastoderma edule (A) and Cerastoderma glaucum (B). Size differences refer to adult shells, arrow heads mark growth lines. C, D Truncate posterior end of the shell of Mya truncata (D) allows discriminating this species from its next relative, Mya arenaria (C). E-O Coiling of the gastropod shells causes sutures (arrows). Ridges, whorls, and outline a species-specific, despite difference in coloration. E-GLittorina littorea, dorsal view (E, F), drawing of ventral view (G). H-KNucella lapillus, dorsal view (H, I), drawing of ventral view (K). L-ONassarius reticulatus, dorsal view (L-N), drawing of ventral view (O). Note intraspecific variation in color, ridges, and curviness in the shown gastropod shells. P, Q Wing veins in Diptera (Hexapoda), d exemplifies one homologous field. PPhilonicus albiceps (Asilidae, Diptera). QMelanostoma mellinum (Syrphidae, Diptera). A, B, G, K, O modified from Hayward and Ryland [70]