Figure 2 : Structure and function of the terminal abdominal segment in a representative species that possesses anal prolegs (Tethea or) and one that lacks anal prolegs but possesses anal oars (Drepana arcuata).

From: The evolutionary origins of ritualized acoustic signals in caterpillars

Figure 2

(a, d) Schematic of T. or and D. arcuata illustrating the overall body plan of each species. (b, f) (top panels) Schematic of identified setae on the terminal segment in T. or and D. arcuata; labels refer to names of setae according to Stehr13 (D=dorsal, SD=subdorsal, V=ventral, SV=subventral, L=lateral, PP=posterior proctor); (bottom panels) scanning electron micrographs showing posterior views of the right anal proleg in T. or and the homologous region with stridulatory oar in D. arcuata. PP1 setae are marked with arrows, and colours correspond to setae labelled in the top panel. Scale bars, 200 μm (T. or) and 100 μm (D. arcuata). (c, e) Video frames of the terminal abdominal segments in each species, illustrating one complete crawling cycle in T. or and one complete anal scraping movement in D. arcuata. Arrows show the progression of movement. Scale bars, 3 mm (T. or) and 1.5 mm (D. arcuata).