JOURNAL OF ULTRASTRUCTURE AND MOLECULAR STRUCTURE RESEARCH 100, 75-85 (1988) La Spermiogenhe de Myzostomum sp. (Procoelomata, Myzostomida) XAVIER MATTEI ET BERNARD MARCHAND Dipartement de Biologie Animale, Faculte des Sciences, Vniversite Cheikh Anta Diop de Dakar, SCnPgal Received March 3. 1988 Le noyau de la spermatide de Myzostomum sp. renferme de la chromatine et des granules de nature proteique. Le centriole unique, donne naissance a un flagelle de type 9 + 0, puis migre dans le cytoplasme de la spermatide. I1 se constitue ainsi un canal cytoplasmique vers lequel migrent les mitochondries. Le noyau s’allonge et 16 a 18 microtubules apparaissent a sa p&iph&ie, organisant une manchette rudimentaire. Le canal cytoplasmique s’ouvre ensuite sur presque toute sa longueur. Le flagelle se trouve ainsi en position extracellulaire. L’enveloppe nucleaire se rompt, mettant en contact direct les elements nucleaires et cytoplasmiques. I1 se constitue ainsi un derive nucleocytoplasmique darts lequel la chromatine est peripherique et les granules protdiques en position centrale. Le centriole, coiffe d’une vtsicule, subit une seconde migration anterieure qui ne se termine que lorsque l’extremite distale du flagelle a depasse l’extremite posterieure du derive nucleocytoplasmique. La partie libre du flagelle constitue de ce fait la portion antetieure du sper- matozo’ide. La vesicule associee au centriole organise une baguette qui fait saillie a I’avant du gamete. Les microtubules de la manchette persistent dans le spermatozoide ou ils sont disposes contre la membrane plasmique. Le spermatozoide est anime de deux types de mou- vements. L’un, peu efftcace, entraine un dtplacement anterograde, flagelle en avant. Nous le supposons dti a des ondulations qui se dtplacent du centriole vers l’extremite du flagelle. L’autre, rapide et e&ace, provoque un dtplacement retrograde, flagelle en arribre. I1 nous semble d0 a l’intervention des microtubules qui dtforment le derive nucltocytoplasmique et impriment au flagelle des ondulations allant de son extremite distale vers le centriole. Q 1988 Academic RW., J~C. The nucleus of the Myzostomum spermatid contains chromatin and protein granules. The single centriole gives rise to a 9 + 0 type flagellum and then migrates in the cytoplasm of the spermatid. A cytoplasmic canal is thus constituted toward which the mitochondria migrate. The nucleus becomes longer and 16 to 18 microtubules appear on its periphery, forming a rudimentary manchette. The cytoplasmic canal then opens along almost its whole length. The flagellum is thus in an extracellular position. The nuclear envelope breaks open, bringing the nuclear and cytoplas- mic elements into direct contact. A nucleocytoplasmic derivative in which the chromatin is pe- ripheral and the protein granules are in a central position is thus formed. The centriole, capped by a vesicle, undergoes a second forward migration which does not end until the distal extremity of the flagellum has gone past the posterior extremity of the nucleocytoplasmic derivative. The free- swimming part of the flagellum now constitutes the anterior portion of the spermatozoon. The vesicle attached to the centriole turns into a rod which protrudes at the front of the gamete. The microtubules of the manchette persist in the spermatozoon where they are arranged against the plasma membrane. The spermatozoon in propelled by two types of motion. The fust, which is not very effective, causes a forward movement, with the flagellum in front. We suppose it is due to undulations which go from the centriole toward the extremity of the flagellum. The second, which is rapid and effective, produces a backward movement, with the flagellum behind. It appears to be due to the intervention of the microtubules which deform the nucleocytoplasmic derivative and transmit undulations to the flagellum, going from its distal extremity toward the centriole. CJ 1988 Academic Press. Inc. Dans une note preliminaire (Mattei et des Acanthocephales (Marchand et Mattei, Marchand, 1987), now avons decrit 1976a, 1977a, b). En raison de cette simili- I’organisation du spermatozoi’de de Myzo- tude, nous considerons les Myzostomides stomum sp. Son anatomie est inhabituelle et les Acanthocephales comme &ant dew et tres proche de celle du spermatozo’ide classes d’un meme phylum que nous avons 75 0889-1605/&J $3.00 Copyright 0 1988 by Academic Press, Inc. All rights of reproduction in any form re~erw~i