Yes, it's true, they're highly toxic... some of them, anyway, and there is no way to know about the specific species you're looking at, so it's safest to assume _all_ of these mat growing polyp corals might be toxic.
Be aware, but really, the risk isn't as great as you might think. There's a poll and a thread on here today about hand washing and gloves. No, I don't use gloves, but hey, it's an option.
Fang toothed blennies (I have a Smith's blenny) are venomous. Most corals and anemones are venomous to some extent, and some people are far more susceptible to their toxins than others. Rabbitfish/foxface (I've got an orange spotted rabbitfish), lionfish... there's lots of critters we keep that may be venomous, to some extent. Be aware, and watch where you stick your fingers
I was in an aquarium shop, many years ago, and watched a teenage employee try and sell a mother and her 10 year old kid a blue ring octopus for the kid's new aquarium. Kid was mad at me for killing the sale by asking the woman if she was aware that the critter she was about to take home was capable of killing her son. Happily, I haven't seen a blue ring in a store for decades, but at one time, it wasn't uncommon to find them.
