These tiny 10 to 15mm diameter cubomedusae, or box jellies, were swept out of some Halimeda algae on a sandy lagoon slope. The four tentacles make it clearly a member of the box jellies, a group best known by its famous member the deadly sea wasp. Most box jellies do possess very powerful nematocysts, but this one is apparently an exception and does not seem to sting.
This appears to be a darker variety. It was in the same habitat and you can barely see the banded tentacles through the bell.
Created 20 October 2015
Updated 23 August 2020