Fig. 4

Line drawings of Macrostomum crassum. a Habitus (dorsal view and lightly squeezed), with sensory cilia (sc), neuropile (np), eyes (e), pharynx (ph), testis (te), ovary (ov), female gonopore (fp), female antrum (fa), shell glands (sg), and adhesive glands (ad). b Male genital system with false seminal vesicle (fv), muscular true seminal vesicle (tv), vesicula granulorum (vg), and stylet (st). c Detailed drawing of the stylet (indicated are the measurements for the straight stylet length and the width of the proximal and distal stylet openings, while the segmented stylet length (in Table 2) corresponds to the average length of both sides of the stylet). d Mature sperm cell with feeler (fe), body (bo), bristles (bi), shaft (sh), velum (ve), and brush (br). Note that it is difficult to distinguish the feeler and body region of the sperm in this species. Scale bars indicate 200 μm in (a) and 20 μm in (b–d)