You saw no lice? Of course not. According to the link submitted by the good doctor, the suspected organism is barely visible except under excellent lighting, appears like a speck of finely ground pepper. Its size is approximately that of a pinhead floating on the surface layers of the water.
As one who spends hours in the Caribbean water every day, at least a week a month and all around the country, I can tell you I've been "stung" and/or come up with itchy rashes many many times, and never have I ever seen what got me, even in the crystal clear waters of Boca Chica, where there is virtually nothing but clean sand underfoot.
There is hardly a day that goes by when I don't end up at least for a few minutes, in an area that has some of that itchy stuff around and I find myself frantically rubbing my hands all over my body to "get it off me". I'm usually not affected for more than a few minutes after I get out of the area. Everybody seems to have a theory about what it is, but make no mistake about it. When you're in it, you'll know it. It isn't jelly fish though. When one of them gets you, thing sting will be instant, intense, at the marks leave lines.
You'll find sea urchins underfoot (venomous points that break into splinters!), sharp rocks, crabs (one reached up and sliced into my toe as my foot dangled above it), plants that if disturbed give off a stinging chemical, fish that will nibble at you, jelly fish, rays that don't take kindly to being stepped on, and a host of critters that sting or bite.
This is not unique to the Dominican Republic. If you swim in the sea or ocean, you can get cut, bit, stung, poked, and get rashes. The sea is alive with life and isn't without risk. Notice that experienced divers often wear wet suits even though the water is very warm. There's a reason.
I always get out of my suit and rinse with fresh water when I get out of the sea. I used to think it was just the salt that made me stingy and itchy.
None of these things would ever keep me out of the water.
