ULTRASTRUCTURE OF SPERMIOGENESIS AND SPERMATOZOA OF DECADIDYMUS-GULOSUS, TEMNOCEPHALA-DENDYI, T-MINOR, CRASPEDELLA SP, C-SPENCERI AND DICERATOCEPHALA-BOSCHMAI (PLATYHELMINTHES, TEMNOCEPHALIDA, TEMNOCEPHALIDAE), WITH EMPHASIS ON THE INTERCENTRIOLAR BODY AND ZONE OF DIFFERENTIATION

Examination of the ultrastructure of spermiogenesis and mature sperm i n six species of Temnocephalidae revealed the origin of the spiral reg ion of microtubules in the sperm shaft. The region is characteristic o f many Temnocephalida but absent from other platyhelminth taxa. During spermiogenesis, an electron-dense heel region develops from, or adjac ent to, the outer plates of the intercentriolar body in the zone of di fferentiation. The intercentriolar body splits into two halves, each o f which remains attached to one basal body via the dense heel. The ent ire anchoring apparatus of each flagellum, consisting of the basal bod y, striated rootlet and the intercentriolar body and dense heel, rotat es around the spermatid shaft until the two basal bodies lie parallel to each other. This rotation causes the compression of one of the two semi-circular rows of microtubules which originate on opposite sides o f the spermatid shaft. The row is compressed to a tight horseshoe shap e with electron-dense material between the folded halves. Distal to th e flagellar insertion region, the shaft tapers and the number of micro tubules decreases. Proximally the inner folded row gradually opens to join the remaining semicircle of microtubules by one end joining the o uter array first. The other end remains inside the peripheral row for some distance, resulting in a spiral arrangement along part of the sha ft. In the six species examined, the proximal end of the sperm termina ted either in an extensive flange that contained only microtubules or by the shaft splitting into a number of fine processes, each containin g only one or a few microtubules.