Histological description of new specialized reproductive structures in Atlantic dendrophylliid corals (Anthozoa, Scleractinia)

Abstract

Abstract The family Dendrophylliidae comprises a genus of exotic azooxanthellate corals, Tubastraea (the ‘sun corals’), native from the Indo-Pacific and introduced in the Atlantic Ocean in the early 40s. In the Southwestern Atlantic, Tubastraea colonies were first registered in oil platforms on the northern coast of Rio de Janeiro State (22°S). Three decades later, the sun corals were for the first time identified in the Todos-os-Santos Bay (Bahia State, 13°S), a warmer environment with pristine marine ecosystems, such as estuaries, mangroves, and coral reefs. Regarding Brazilian native corals, studies on reproductive biology were developed for the broadcast spawner genera Madracis, Montastraea, and Mussismilia, as well as for the brooder corals Astrangia, Favia, Porites, Scolymia, and Siderastrea. Intending to describe the biological cycle of exotic dendrophylliids from the Brazilian northeastern coast, histological analyses revealed the occurrence of three new reproductive structures never yet observed in Scleractinia. The trophonema is commonly found among actiniarians and has also been registered for antipatharians, zoanthids, and coenothecalians (Alcyonaria). Similarly, an envelope of glycoproteic matter surrounding immature oocytes has never been mentioned for hard corals. Finally, the nucleolinus was thought to be restricted to mollusks and vertebrates, being an indicator of fertilized or parthenogenetic eggs. For the first time, the trophonema, the glycoproteic sac, and the nucleolinus are identified and described for Scleractinia. Beyond unexpected adaptative trends in the reproduction of the sun corals, these unprecedented results consolidate the knowledge about the anatomy and biology of basal metazoans.