Oceanic mixotrophic flatworms

Abstract

Most reports of photosynthetic flatworms are from benthic or littoral habitats, but small 1 mm) acoel flatworms with algal endosymbionts are a widespread, though sporadic, component of the open-ocean plankton in warm waters. Among oceanic flatworms are specimens harboring prasinophyte or, less commonly, dinophyte endosymbionts. Photosynthesis was measured by super(14)C uptake in flatworms from shelf/slope waters in the western north Atlantic and from the Sargasso Sea. Rates were as high as 27 ng C fixed ind./h. Assimilation ratios ranged from 0.9 to 1.3 ng C fixed (ng Chlorophyll a)/h. Although these acoels were photosynthetic, they were also predatory on other plankton.