Description of Euplotes charon: Medium (70-96 microns long) oval marine hypotrich ciliate which has a very large open triangular peristomial region. The right margin of the peristome winds sinusoidally down past the cytostome to about 7/8 of the body length. The abdoral zone of membranelle bears approximately 70 strong membranelles while the abdoral zone of membranelle as a whole extends down to about 2/3 of the body length. The dorsal argyrome is of the double-eurystomus type with 12 dorsolateral kineties carrying 18-40 dorsal cilia in the mid-dorsal rows. There are 10 frontoventrals, 5 transverse and 5-8 caudal cirri. The macronucleus is horseshoe shaped and there is a small compact micronucleus situated anteriorly.