Some aspects of the oogenesis of three species of clathrinid sponges (Calcarea, Porifera)

Although oogenesis is the best-known stage of development in sponges of the subclass Calcinea (Porifera, Calcarea), several aspects of this process await further investigation. In the present study, we examined by light and electron microscopy the oogenesis of three species of the order Clathrinida (Clathrina aurea, Borojevia aspina and B. brasiliensis) from the coast of Rio de Janeiro state (Brazil). Oogenesis in these species was a rare and not synchronized event, neither in the individual nor in the population level. Oocytes grew between the choanoderm and the pinacoderm. They did not form any special structure for nourishing the egg and phagocytosis of somatic cells was not observed. The vitellogenesis of B. aspina and B. brasiliensis was performed in a mixed pathway, while in C. aurea it was not possible to observe the vitellogenesis. In the Borojevias, the surrounding choanocytes provided small clear vesicles at the same time that oocytes modified phagosomes to produce fibrous yolk inclusions. The phylogenetic character mapping analysis indicated that egg development in the mesohyl is the ancestral state for Calcinea, while the ancestral condition of the vitellogenesis is still uncertain.