The function of the eye-like ocelloid in warnowiid dinoflagellates remains unknown because warnowiids are rare and uncultured, and scant molecular data exists for this group. While the ocelloid resembles the camera-type eyes found in animals, it is composed of organelles, with a highly modified plastid serving as the retinal body. By performing single-cell transcriptomics on cells isolated from the environment, we generate a comprehensive molecular dataset of warnowiids that includes all four known genera and one previously undescribed genus. We show that the heterotrophic members of this group have retained and express components of the ancestral photosynthetic mechanism, seemingly without photosystem II and RuBisCo. Our findings suggest that the ocelloid retinal body has repurposed the remaining photosystem to perform a function other than photosynthesis.

Cells of interest were isolated using a microcapillary pipet and placed into lysis buffer. cDNA extraction was performed according to SmartSeqII (Picelli et al. 2014). Libraries were prepared at the Sequencing and Bioinformatics Consortium, University of British Columbia, and sequenced on the Nextseq platform.