Ultrastructure and large subunit rDNA sequences of Lepidodinium viride reveal a close relationship to Lepidodinium chlorophorum comb. nov. (= Gymnodinium chlorophorum )

The chloroplasts of dinoflagellates display an unusually high diversity. Therefore, besides the typical peridinincontaining chloroplast probably of red algal origin (Ishida & Green 2002), some dinoflagellate chloroplasts have originated from a cryptomonad, diatom, haptophyte or chlorophyte (Watanabe et al. 1987, 1990; Elbrachter & Schnepf 1996; Chesnick et al. 1997; Schnepf & Elbrachter 1999; Takishita et al. 1999; Hackett et al. 2003). It has recently been hypothesized that the seeming readiness of dinoflagellates to take up and incorporate foreign chloroplasts might rely on the exceptionally high number of chloroplast genes transferred to the dinoflagellate nucleus from the original chloroplast (Green 2004). As acquisition of chloroplast-containing endosymbionts seems to be a relatively frequent event in apparently diverse groups of dinoflagellates, the chloroplast type and color have not been considered to be useful taxonomic criteria above species level (Elbrachter & Schnepf 1996). However, recent investigations based on molecular sequences have quite surprisingly shown that the diatom- containing dinoflagellates form a monophyletic group (Inagaki et al. 2000; Horiguchi 2003; Tamura et al. 2005; Horiguchi & Takano 2006), irrespective of the fact that this group consists of morphologically very diverse species (e.g. athecate, thecate, flagellate, coccoid and filamentous forms). This indicates that the acquisition of endosymbionts might not be so frequent a phenomenon as hitherto anticipated and that chloroplast type might be a taxonomic criterion to be used also at higher than species level.