Stingray, in the hand. Didn't see it because it was buried in the sand. I accidentally brushed my hand over it in shallow water when I was just starting to swim to deeper water. Even had heavy leather gloves on. Also been stung by an agua mal (man o' war) when I swam into a broken off piece of tentacle a couple times. Pretty common in Rocky Point in the warm months. Only other thing I've ever been stung by is sea nettles - the invisible kind. You don't even see those, just feel the stinging. They are some kind of small plankton critter or tiny jellyfish.
Some of the tide pools along the Miramar are pretty large. At low tide, after the sediment settles, you can snorkel in them and see lots of neat critters that aren't obvious just by poking around up on top. Brittle stars, octopus, nudibranch, gobies, tube worms -- literally all kinds of colorful and interesting stuff.