design: Hosts were collected from the reef in front of CARMABI station on Curaao. The hosts were dissected and had their intestines removed, sliced into smaller pieces in sterile 0.2 m-filtered seawater and agitated by pipetting. The liquid was examined for archigregarines using a Leica DMIL inverted microscope. Archigregarines were manually isolated with a glass micropipette, washed 3-6 times in 0.2 m-filtered seawater, and imaged at 200x-400x magnification with a Sony alpha 7R camera. A single cell was then deposited in SmartSeq2 lysis buffer for single-cell transcriptomics (Picelli et al 2014). Cells were subjected to two to three freeze/thaw cycles, after which cDNA was generated and amplified following the SmartSeq2 protocol, using 24 PCR cycles. The resulting cDNA was made into libraries with Illumina Nextera XT or Illumina DNA prep, and sequenced on a Illumina MiSeq run (2x250 bp paired end).