Well, here it is. The true identity of the beastie will probably be disappointing to some readers and revolting to others. This is my new monster, which is both predatory and venomous...so still kind of cool, right?
For reference, that specimen container it's in is about 5.5" (14cm) across, and the worm snakes back and forth across it twice and a bit more when
retracted. It is as big around as my thumb in that state. When I saw it earlier today, it was stretched completely across a 3ft/1m tank having a snuffle about in some detritus. It was strong enough to shrug off the long metal forceps that I use to snare normal-sized worms, so catching it was a bit of a fun time.
Although I have seen and heard of some pretty big fireworms over time, this one takes the cake from my own experience and reading. All of the dreaded worm-as-long-as-your-arm stories I've heard and read in the hobby have been Eunicids, but this one seems to be an actual fireworm. It's quite pretty really...bubblegum pink and iridescent. I was sorely tempted to get a silly floral pattern tank for it but it was the wrong dimensions to fit any place I had to put it. However, it's flamboyant pinkness doesn't make it safe. It's a size that can easily take out shell-dwelling animals like hermits, snails, and Bivalves...and guess what has been turning up as empty shells for me lately in that tank! The way it whipped about when I was trying to catch it almost got me stung several times too since it was longer than the forceps I was using. I am pretty sure that it's not just a massively overgrown individual of a common species; it has some unusual features like obvious eyes. And it uses those eyes...I had to cover the specimen cup to stop it from being a total creeper and sticking its head over the side to look around the room. NOT something I want to see taking a stroll across the floor in a random part of the house.
So, there is a giant worm coiled up inside that pico now...and have to keep my fingers crossed that it was just a lone oddball and didn't establish a colony before showing itself to me today.