Bearded Fireworm: A macro study of a mean-looking polychaete

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They look like a cross between a caterpillar and a tricked out centipede. They crawl about with considerable agility, they are voracious feeders, and they certainly know how to defend themselves. Meet the Bearded Fireworm (Hermodice carunculata), a free-moving marine Polychaete worm.

This species is widely distributed from the Caribbean, throughout the warmer waters of the Atlantic Ocean (including Florida and the Bahamas), and all the way to the Mediterranean Sea. All of the images in this post were captured in the Mediterranean, in the waters around Cyprus and Greece.

H. carunculata is a segmented worm, i.e., it is a member of the phylum Annelida. As a Polychaete, one of its distinguishing anatomical features is a set of bristles. In this case, the hair-like bristles, or setae, are arranged in bundles attached to small appendages, called parapodia, at the lateral edge of each segment of the worm.

Although the setae are very fine, they are hollow and contain a venom. The setae also are extremely brittle. If touched they will break off readily and the fragment(s) will lodge in the skin of whatever touched them. The common name Fireworm refers to the burning sensation caused by the venom in the setae.

When the animal is disturbed or threatened, the setae are fluffed out in a defense display, as in the photo below.

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In the next photo, below -- a sort of quarter-profile view -- you can see the how the setae bundles emerge from the critter's parapodia. The structures above the parapodia are gill filaments. Also visible is the worm's median antenna, looking a bit like a thin rhinoceros horn.

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The species name of H. carunculata refers to the fleshy orange bit on its head, called a caruncle. The caruncle is believed to have a sensory function. The head-on macro shot below presents a more detailed view of the worm's prostomium, with all of its associated parts. (Don't be afraid; it looks fierce, but it's only a photo!)

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One final photo will put things back into perspective. In the image below, we see the whole animal as it goes about its business in the muck. This individual was not feeling very threatened, so its setae are semi-retracted.

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Speaking of muck, taking photos like these is not a task for the squeamish. Setting up the shots requires that the photographer spend a considerable amount of time lying on her belly in the muck, surrounded by these creepy-crawly critters.

All of the individuals in the above images were between 10 cm and 15 cm (4 in to 6 in) in length. I am told that H. carunculata can grow to a length of 30 cm (12 in) -- but for the record, I have never seen one that long, nor would I care to!

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Why would you not care to see a huge fireworm? The only danger is brushing against them and getting stung, and a large one would be easier to avoid!

Hello Vasha - You are right, of course. My aversion to the thought of a very large fireworm has nothing to do with fireworms, per se, and everything to do with their superficial resemblance to centipedes. I have been bitten by a large centipede, and it was extremely painful, so the sight of anything even remotely resembling a centipede is a bit off-putting, and the thought of a foot-long centipede-resembling creature gives me the creeps. It's a personal thing.

That is fantastic. It interests me that the median antenna is not used for defense (right?) despite how vicious it looks (at least at the macro level), but the more placid setae carry the venom. I suspect I would be one of the dumber natural enemies of this creature, going after the kinder, softer looking parts and getting a mouthful of ouch.

(Funny to note this post appears on the day when I started reading Thomas Eisner's Secret Weapons: Defenses of Insects, Spiders, Scorpions, and Other Many-Legged Creatures...I think this just added another unofficial chapter).

This is wonderful! I've tried to photograph similar polychaetes, without much success. These photos are beautiful.

May I use the post in the upcoming Circus of the Spineless? (This month, I'm hosting, on my blog.)

@ Fetanish - I wish I could say for sure whether the median antenna also has some role in defense, but I have no idea. I first saw that structure on my own macro photos of this creature, and I did not know what it was. Eventually I found a taxonomic description that mentioned the median antenna, but it did not elaborate on the function of the antenna. It certainly looks like it could do some damage, doesn't it?

@ Susannah - Thank you. These critters are a bit difficult to photo in macro mode, since they seem to move almost constantly. My hunch is that they sense a pressure wave from anything that gets close to them, including photographers! I can't tell you how many attempts it took before I got a few images that were usable.

I would be delighted to have this post included in the Circus of the Spineless. Thank you for asking.

In the macro, it looks like a horned pekingese! Is it possible this is the true identity of these alleged "dogs"?

Beautiful shots! Did you deliberately threaten them for the shot (to get the defensive reaction), or are they easily disturbed?

@ Anon - Pekingese? Well that is a novel description! No, I did not intentionally threaten them. They are very easily disturbed. In fact it is difficult to get close to one of these critters (as is necessary for macro photos) without them sensing the nearness and fluffing out their setae.

@ Monado, FCDr - Yes, it probably is a similar mechanism: "I may be small, but touch me at your peril!"

Hi Susannah - Thank YOU for including the post in this month's Circus of the Spineless. :)

I'm am researching the bearded fireworm for a science project, and I was wondering: what do they eat, do they move in the same way that earthworms do, does the fireworm live completeley submerged in water or does it just live near water, how long does it live, and what kind of habitat does the worm live in? If you could answer my questions that would be an enourmous help! Thank You!

It appears that the paint is under high pressure and cannot emerge without a great deal of turbulence. Unlike the contents of the egg, the exploding paint has no obvious symmetries. To my eye at least, the egg is beautiful and the paintball ugly.

how long does it live, and what kind of habitat does the worm live in? If you could answer my questions that would be an enourmous help! Thank You!

I agree with conclusion you make; the more I read, the more skeptical I become. Nothing is particularly compelling tell.

It appears that the paint is under high pressure and cannot emerge without a great deal of turbulence. Unlike the contents of the egg, the exploding paint has no obvious symmetries. To my eye at least, the egg is beautiful and the paintball ugly.

I agree with conclusion you make; the more I read, the more skeptical I become. Nothing is particularly compelling tell.