Ultrastructure of spermiogenesis and spermatozoa of Discocotyle sagittata (Monogenea : Polyopisthocotylea : Discocotylinea)

Ultrastructural analysis revealed that the spermatozoon of Discocotyle sagi ttata (Leuckart, 1842) is composed of two parallel axonemes, mitochondrion, nucleus and cortical microtubules. The nucleus, which occupies a central/d istal position and has an unusual crescent-shaped profile, is slightly shor ter than the mitochondrial rod. The two axonemes, which are of unequal leng th, and the cortical microtubules (up to 68 forming a continuous ring in th e principal region) extend almost the entire length of the, spermatozoon. A fold of the plasma membrane creates a unilateral flange or undulating memb rane. Epifluorescence microscopy indicated that spermatogenesis gives rise to clusters of 64 spermatids connected to a common cytophore. Spermiogenesi s and the structure of the filiform sperm of D. sagittata conform to the ty pical polyopisthocotylean pattern.