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

Abstract

Spermatogenesis ultrastructure was studied in a simultaneous hermaphrodite population of the solitary coral Balanophyllia europaea. In this species, spermatogenesis takes place in spermatocysts located within gametogenetic mesenteries surrounded by a bilayered boundary. Spermatogonia and spermatocytes are large flagellate cells, densely packed at the outermost edges of the spermatocyst. Spermatids and sperm are loosely distributed near the centre of the spermatocyst. The cytoplasm of spermatogonia and primary spermatocytes often contains short lengths of free axonemes, probably derived from the reabsorption of a primitive flagellum. Maturing spermatids either contain long intracytoplasmic axonemes, that may be stages of the tail synthesis, or have a flagellum. The morphological features of the sperm of this hermaphroditic scleractinian, very similar to those observed in the sperm of gonochoric taxa, support the hypothesis that the hermaphroditism of this population is an adaptive condition.

Sexual reproduction in the Mediterranean solitary coral Balanophyllia europaea (Scleractinia, Dendrophylliidae)

“…In particular, for species living in the Mediterranean, information is available only from the 19th century, on Caryophyllia smithi, Astroides calycularis, Balanophyllia regia, B. pruvoti and Cladopsammia rolandi (Lacaze-Duthiers 1873, 1897, and from the last few years on B. europaea (Goffredo & Telò 1998, Goffredo et al 2000.…”

“…A total of 94% of dendrophylliid corals studied are gonochoric (Harrison 1985). Of 50 known species of Balanophyllia (Cairns 1977), reproductive modalities are known only for B. pruvoti at Marseilles, France (Lacaze-Duthiers 1897), B. elegans at Monterey Bay, California (Fadlallah & Pearse 1982a, Beauchamp 1993 and B. europaea at Leghorn, Italy (Goffredo & Telò 1998, Goffredo 1999, Goffredo et al 2000. All are brooders; the first 2 species are gonochoric and the latter is hermaphroditic.…”

Dicyemid’s dilemma: structure versus genes. The unorthodox structure of dicyemid reproduction

“…Spermiogenic cells develop there without intercellular bridges, each within its own given time. A similar situation was found in a basal metazoan, the solitary coral Balanophyllia europaea in which spermiogenesis also takes place in an unsynchronized manner caused by the lack of intercellular bridges (Goffredo et al 2000). Another interesting phenomenon is the presence of annulate lamellae, not only in spermiogenic cells but also in the infusorigen's axial cell.…”

“…This somatic condition, which apparently points to plesiomorphy, is based on three particular organelles determining the mature sperm: the uncondensed state of the nucleus with its persisting pore complexes, the adaptation of the bundle of microtubules to a tool for fertilization and, finally, the lipid vesicle connecting both of these organelles. This uncommon concept essentially contradicts the ground pattern of metazoan sperm morphology, whose fundamental synapomorphies are shared with lophotrochozoans, both freeliving and parasitic ones (Jamieson et al 1995), as well as with such basal phyla such as Porifera and Cnidaria (Hinsch 1974;Paulus 1989;Goffredo et al 2000). This pattern is founded on a tripartite organization (Baccetti and Afzelius 1976): (1) the head, represented by a nucleus of predominantly condensed chromatin generally covered by a nuclear membrane devoid of pore complexes and the whole thing mostly surmounted by an acrosome; (2) a middle piece surrounded by mitochondria metabolizing the energy needed to propel; and (3) the flagellum, which arises from the posterior centriole.…”

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;.…”