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.
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.
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!)
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.
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!