Musculature of the posterior trunk region and spines in Echinoderes. (A-B) Confocal z-stack projections of phalloidin staining (muscle, red) and autofluorescence (cuticle, grayscale) in segments 9–11 of Echinoderes horni (A) and Echinoderes spinifurca (B) in ventral view, with posterior to the bottom. (C-D) Confocal z-stack projections of phalloidin staining in the posterior end of Echinoderes horni (C, male) and Echinoderes spinifurca (D, female) in lateral view, with posterior to the right side. (E-F) 3D reconstruction of myoanatomy in segments 7–11 of Echinoderes spinifurca in lateroventral view with posterior to the right side. Autofluorescence of the cuticle is included in (F). Abbreviations: dm, dorsal muscle; dvm, dorsoventral muscle; hd, hindgut dilator; LTAS, lateral terminal accessory spine; LTS, lateral terminal spine; pm, penile spine muscle; ps, penile spine; s, segment; te, tergal extension; tem, tergal extensions muscle; tsd, terminal spine depressor; tsl, terminal spine levator; vm, ventral muscle. Digits in (A) and (B) refer to the segment number. Scale bar: 20 μm.