Abstract
The technique of serial sections has been employed to study spermiogenesis and spermatozoon of Gonapodasmius. The zone of differentiation (ZD) shows no centriole-like body and no striated root. Peripheral microtubules are of two types: laterally placed thick microtubules which are spaced and coincide with external bristles on the membrane; and dorsally and ventrally placed thin microtubules which are closely aligned. The two parallel flagella fuse with the median cytoplasmic process. The nucleus, mitochondrion, and thin microtubules migrate distally. The arching membranes, at the base of the ZD, mark the area where the mature spermatozoon is pinched off from the cytoplasmic mass. The spermatozoon consists of four regions. (a) The anterior region, made of the ZD, has peripheral microtubules with external bristles, viewed in toto as longitudinal ornamentations. Two centriolar derivatives, made up of nine singlets each, are continued as two 9+“1” flagella, classic in Platyhelminthes. (b) The intermediate region shows no peripheral microtubules. (c) The middle region shows nucleus, mitochondria, and ventral microtubules without ornamentations. (d) In the terminal region, the two flagella separate. The first two regions have never been described in previously studied Platyhelminthes spermatozoa.
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