Looks like an ant, or part of an ant, to me. Seriously, may be terrestrial contamination. Looks EXACTLY like an ant head with attached throaz, legs may have been broken or pulled off. Is there a toddler on mars playing cruel ricks with happless insects and marsophiles?
I think a full OM image is 1 mm. That surely is not more than 1/10 across, so maybe 100 microns? The smallest ant I have seen (a small black ant) is about 1 mm.