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Cover
Dinoflagellates are a diverse and ecologically important group of unicellular protists. Some of them are free-living, photosynthetic or heterotrophic constituents of the plankton; others are symbiotic. Dinoflagellates in the genus Symbiodinium, commonly called zooxanthellae, are intra- or intercellular symbionts of diverse marine invertebrates, including foraminiferans, sponges, cnidarians, and molluscs.

The image on the cover shows a throng of Symbiodinium kawagutii cells that were isolated from their symbiotic host, the Hawaiian stony coral Montipora capitata (= M. verrucosa)¹; the coral appears in the inset. In 1987, on the basis of cytological evidence, R. J. Blank² speculated that the vegetative cells of M. verrucosa are haploid; but this finding was never corroborated. The question of ploidy is important, for it is central to our understanding of genome evolution and population genetics.

Now, for the first time, the methods of molecular genetics have been applied to the problem of haploidy in dinoflagellates. In this issue of The Biological Bulletin (p. 10), Scott R. Santos and Mary Alice Coffroth report that vegetative cells of Symbiodinium clade B symbiotic with gorgonians (sea fans and sea whips), and cultured cells from a range of hosts and locations, are haploid. Moreover, since Symbiodinium is monophyletic, S. kawagutii and other members of the genus must also be haploid.

The Symbiodinium cells on the cover are about 10 m in diameter; they were photographed by Scott R. Santos (State University of New York at Buffalo). The photograph of Montipora capitata was taken by Frank Stanton (University of Hawaii) at a depth of about 1.5 meters; the coral is about 1 m in diameter. Materials and information for the cover and legend were provided by Fenny Cox (University of Hawaii). The cover was designed by Beth Liles, Marine Biological Laboratory, Woods Hole, Massachusetts.

¹Maragos, J. E. 1995. Revised checklist of extant shallow-water stony coral species from Hawaii (Cnidaria: Anthozoa: Scleractinia). Bishop Museum Occasional Papers 42: 54-55.

²Blank, R. J. 1987. Cell architecture of the dinoflagellate Symbiodinium sp. inhabiting the Hawaiian stony coral Montipora verrucosa. Mar. Biol. 94: 143-155.


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