AME 62:279-287 (2011)  -  DOI: https://doi.org/10.3354/ame01474

ABSTRACT: We documented the abundance of the heterotrophic dinoflagellate Oxyphysis oxytoxoides Kofoid along the Korean coast, cultured it (food source: the marine ciliate Myrionecta rubra Jankowski [= Mesodinium rubrum Lohmann]), sequenced its nuclear-encoded large-subunit (LSU) rDNA, and resolved its phylogenetic relationship within the Dinophysiales. Abundance was low, usually <9.7 × 10³ cells l^–1, in samples from 2005 and 2006. It co-occurred with the mixotrophic dinoflagellate Dinophysis acuminata, possibly indicating a common pool of prey. Growth on M. rubra reached a density of 38 × 10⁵ cells l^–1. Observations on live cells from our established cultures revealed that O. oxytoxoides uses a peduncle to suck up the cell contents of M. rubra, the number of food vacuoles increasing as feeding proceeds. No regional variability was found in partial LSU rDNA sequences (domains D1–D2) of our strains, despite different sampling sites and dates. Phylogenetic analysis, based on LSU rDNA, showed that while Amphisolenia forms an early divergent basal group in the Dinophysiales, the other dinophysoids form 2 separate groups: (1) Oxyphysis and Phalacroma, and (2) Histioneis, Ornithocercus, Citharistes and Dinophysis. The presence of a peduncle in several genera, and the widespread distribution of pedunculate dinophysoids, indicate that these species may be fundamentally heterotrophic with a common feeding mechanism. Our results shed light on the feeding ecology and phylogenetic position of O. oxytoxoides.

KEY WORDS: Dinophysiales · Myrionecta rubra · Oxyphysis oxytoxoides · Peduncle feeding · Phylogeny