Spermatogenesis in anthozoa: Differentiation of the spermatid

Abstract

The fine structure of spermatids has been examined in Calliactis, Protanthea, Gonactinia and Parazoanthus (Cnidaria, Anthozoa). The sperm cells are relatively simple and lack distinct acrosomes. Their nuclei, spherical in the zoanthid, in the actinians are slendertipped cones. Condensation of the chromatin is interpreted in terms of progressive coiling of densely-stained filaments and the elimination of nucleoplasm. Nuclear elongation occurs in the absence of microtubules. A well-developed centriolar complex is attached to the nuclear envelope by fibres and in this area (that of a shallow fossa in actinian spern) the nuclear membranes seem to be thickened. The centrioles are surrounded by a mitochondrial collar, especially pronounced in Calliactis. In contact with the mitochondria and nucleus is a ring of lipid-containing vesicles 300-700 nm in diameter. A system of densely-staining vesicles 150-300 nm in size corresponds to the "pro-acrosomal vesicles" described for other coelenterates. They are scattered in the peripheral cytoplasm and are regarded as derivatives of the endoplasmic reticulum. Problems of organelle function and of differentiation during spermiogenesis are discussed.

Ultrastructural observations of the spermatogenesis of the hermaphroditic solitary coral Balanophyllia europaea (Anthozoa, Scleractinia)

“…The main nuclear maturation stages in B. europaea spermatids are substantially the same as those described in other Anthozoa (see Dewel and Clark 1972;Clark and Dewel 1974;Lyke and Robson 1975;Larkman 1980; In the posterior region of the cell an axoneme, many disassembled doublet microtubules (arrow) and four mitochondria are present. B Spermatid.…”

“…Cytoplasmic microtubules, which play a role in nuclear shaping of many Metazoa (Baccetti 1970;Adiyodi and Adiyodi 1983), were not observed. For this reason, one can assume that nuclear shaping in B. europaea is determined by chromatin aggregation and condensation, as already suggested by Lyke and Robson (1975) for other anthozoans. When chromatin condensation is complete, a small bullet-shaped area of slightly electron-dense material is evident at the anterior tip of the nucleus in B. europaea sperm.…”

“…Larkman (1980), Schmidt and Hoeltken (1980) and Hinsch and Moore (1992) studied the early phases of Anthozoa spermatogenesis. Clark and Dewel (1974), Lyke and Robson (1975) and Schmidt and Zissler (1979) carried out most of the available observations on spermiogenesis in Anthozoa. Recently, much attention has been given to the ultrastructural features of mature sperm in Scleractinia (Harrison 1988;Steiner 1991Steiner , 1993Steiner and Cortés 1996).…”

Gamete spawning in Antipathella subpinnata (Anthozoa, Antipatharia): a structural and ultrastructural investigation

“…Gradually, however, the sexual reproduction of corals has received greater attention. Ultrastructural studies have significantly contributed to expanding our knowledge of gametogenesis, mature gamete structure, fertilization and ensuing development (Hinsch and Clark 1972;Hinsch 1974;Clark and Dewel 1974;Lyke and Robson 1975;Schmidt and Zissler 1979;Schmidt and Schäfer 1980;Steiner 1991Steiner , 1993Goffredo et al 2000;.…”

Existence d'un complexe acrosomal chez les spermatozoïdes du cnidaireMuggiaea kochi(Siphonophore, Calycophore): différenciation et réaction acrosomale / Existence of an acrosomal complex in the spermatozoids of the cnidarianMuggiaea kochi(Siphonophora, Calycophora): differentiation and acrosomal reaction

“…Cela semblait Ia regie chez les spermatozoides de cnidaires oil seules des petites vesicules qualifiees de proacrosomiques avaient ete observees, chez certaines especes, pres du pole anterieur du noyau [1][2][3][4].…”