Fig. 4

Terebra of Lariophagus distinguendus. a–d Light microscopical images of semithin cross sections through the terebra (from proximal to distal; scale bar in d applies to all light micrographs; positions of the sections are indicated in Fig. 6c; cf. Additional file 3). The bulbs and the laminated bridge are visible proximally. The 2nd valvula is connected with the paired 1st valvulae via the olistheter system. e–k TEM images of the terebra of L. distinguendus. The cuticle of the valvulae is remarkably homogenous. e Parts of the laminated bridge on the proximal part of the 2nd valvula (cf. a). f Notal membrane (cf. c). g Olistheter system comprising the rhachis of the 1sr valvula and the aulax of the 2nd valvula. h–k Apical part of the terebra. The olistheter-like interlock of the 1st valvulae on their dorsomedial surfaces (h, I, k) and the coeloconic sensillum at the apical end of one aulax are visible (j; for overview image, cf. Fig. 3a). Abbreviations: 1vv: 1st valvula; 2vf: 2nd valvifer; 2vv: 2nd valvula; 3vv: 3rd valvula; au: Aulax; blb: Bulb; cs: Coeloconic sensillum; den: Dendrite; ec: Egg canal; il1: Interlock of the 1st valvulae; lb: Laminated bridge; le: Lateral extensions of the 2nd valvula; lu2: Lumen of the 2nd valvula; m-1vf-gm: 1st valvifer-genital membrane muscle; nm: Notal membrane; oth: Olistheter; rh: Rhachis; st2: Sawtooth of the 2nd valvula; vw2: Ventral wall of the 2nd valvula