English: Figure 16 of the paper.

Diagrams of spermatozoa (redrawn from Justine, 1991).

Caption adapted from original caption of figure. Diagrams were drawn from original micrographs of transverse sections. Digenea. Dorsal and ventral microtubules are present (proposed as a synapomorphy for the Cercomeridea). There are no lateral microtubules (symplesiomorphic compared with the synapomorphy for the polyopisthocotylean Monogenea). Polyopisthocotylea. Dorsal and ventral microtubules are present (synapomorphy for Cercomeridea). Note the presence of lateral microtubules (proposed as a synapomorphy for the Polyopisthocotylea). Monopisthocotylea (uniflagellate and biflagellate). Microtubules are absent from the principal region of the spermatozoon, which is interpreted as (i) the absence of dorsal and ventral microtubules, a reversal of the synapomorphy for the Cercomeridea; and (ii) the absence of lateral microtubules, the symplesiomorphic state versus the synapomorphy for the Polyopisthocotylea.