Schematic reconstruction of the mature spermatozoon for the family Pleurogenidae. The sperm cell is organized in three different regions: Region I or anterior part, Region II or middle part and Region III or posterior part. The blue discontinuous lines linked to the first and second mitochondria indicate the more posterior location of the two mitochondria in the spermatozoon of Prosotocus confusus. Consequently, in P. confusus cross-sections marked with * do not present mitochondrion and the section marked with ** only exhibits the first mitochondrion. ASE, anterior spermatozoon extremity; Ax1, first axoneme; Ax2, second axoneme; AZ, attachment zones; C1, centriole of the first axoneme; C2, centriole of the second axoneme; CC, central core; CM, cortical microtubules; D, doublets; EO, external ornamentation; G, granules of glycogen; M1, first mitochondrion; M2, second mitochondrion; N, nucleus; PM, plasma membrane; PNE, posterior nuclear extremity; PSE, posterior spermatozoon extremity; S, singlets; SB, spine-like bodies.