These are animals the Phylum Annelida, Class Polychaeta, Family Amphinomidae.  Commonly they are called: Bristleworm, Fireworms; Large Scavenger Fireworms.

Eurythoe complanata.   Left. A Eurythoe foraging on some Caribbean sand.  Right: A close-up of the head region of an adult Eurythoe collected from an aquarium.

Eurythoe complanata

These worms are the Bristleworm's bristleworms! Almost every novice aquarist gets a big shock when they see their first large bristleworm, which is almost always a large specimen of the common Caribbean Fireworm, Eurythoe complanata. The general reaction is one of disgust, dislike, fear and loathing. 

Such reactions are based on ignorance; these are some of the most beneficial animals that it is possible to have in a marine reef tank. Eurythoe individuals are scavengers and will only consume or dying animals.

Reports of them attacking live animals have universally been shown to be reports of them being first on the scene of newly dead animals as efficient scavengers. 

They also may occasionally remove food from a coral or sea anemone. 

The worms typically live in crevices or holes in the rockwork of a tank and come out to scavenge after dark or after a good feeding. Because of their rock-dwelling habit, they enter tanks in newly purchased live rock or in the bases of coral. They worms may reach large sizes, lengths up to 40 cm (16 inches) have been reported. 

They have a number of distinguishing physical characteristics: 

There is no special care necessary to keep these animals in a normal reef system. In addition to the their beneficial attributes as scavengers, a thriving population of these worms will spawn regularly producing larvae that are eaten by many small polyped corals and other zooplankton predators. Some aquarists try to remove Eurythoe complanata from their tanks, but such individuals are misguided and ultimately working against their tank. All fireworms, including Eurythoe , are dangerous to the touch. Their white bristles are calcareous, fragile and hollow.  They may be filled with a venom released when they  fracture. Additionally the bristles are barbed and appear designed to pierce flesh.

When a predator, or an unwary aquarist, tries to pick up a fireworm, the bristles pierce its flesh, break, and release the venom, which functions as an irritant. While the irritation to humans is typically mildly irritating, it may be significantly painful in sensitive individuals. If you need to hand these worms it is best to use forceps, or where gloves.

Hermodice carunculata

Hermodice carunculata.  Left.  Top of the head showing the caruncle or fringe of tentacles.  This is a distinguishing characteristic, no beneficial fireworm has these.  A Hermodice (right) feeding on a gorgonian, the worms has ingested the end of the gorgonian's branch and is licking off the tissue.  


In contrast to the other large beneficial fireworms found in our tanks, one species decidedly presents problems for a reef aquarium. This species, Hermodice carunculata , is a fireworm species commonly found in the Caribbean, although other species in the same genus are found throughout the tropics. It is the only potential “problem” fireworm in aquaria because it eats stony corals and gorgonians in its natural habitat, but may also prey on soft corals in the aquarium. As with all fireworms, this species has no jaws to bite off chunks of food, rather it must lick them to death.

A scanning electron micrograph of the front end of a Hermodice individual; (M= the mouth, P= the parapodia, and C= fringe-like tentacles found on the caruncle).


As the worm lacks the jaws to sever the pieces of its prey, feeding in Hermodice is a prolonged process. When they feed, Hermodice individuals typically swallow the ends of a gorgonian or soft coral and then proceed to lick the flesh off of it, while the ends are still attached to the colony. Such feeding is a lengthy process; it takes hours. During this period the worm really isn't going to go anywhere, it is tethered to its dinner. This species is also an obligate predator of these prey, although it may scavenge a bit, it will not, - in fact, it cannot, - eat other prey.  If you have a Hermodice in your tank, you will either eventually find it on a prey organism munching away or see it crawling across the substrate. Remove it with a pair of forceps, tweezers, or tongs, and dispose of it.

Other Fireworms

Linopherus (?) sp.  One of the many smaller species that thrive in reef aquaria.  This image shows about half of the worm.  These worms are quite common in reef aquaria, and reach lengths around an inch (2.5 cm) or so. 


Another common, but unidentified, and beneficial scavenging fireworm found in aquaria.  This worm reaches lengths of 5 to 7.5 cm (2 to 3 inches).


The reproduction of the smaller fireworms that are also common in our systems, in the genera Linopherus or Pareurythoe, is less obvious, but they also can maintain quite stable and large populations in our systems. Most of the fireworms found in our tanks are in these latter two genera, and these animals occupy burrows in the sediments as well in holes in the rockwork. If not hassled by fish or crustaceans, they may be seen commonly during the day looking for food and doing their other wormy activities. These smaller species may reproduce more frequently by asexual than sexual means as indicated by the abundance of worms that are regenerating either front or back ends. As with the small starfish that are common in some reef aquaria, these worms reproduce asexually by fission, after which both halves produce the missing component.

Scale Worms

A photo of a small scale worm contributed by Nicholas Allers.  The worm is inside the blue line and a few of the scales characteristic of these worms are indicated.  The head of the worm is to the left and the antennae of the worm are visible extending out from under the scales.  The scales on this worm cover the entire upper surface.


Scale worms are small polychaete annelids or bristle worms that are scavengers or predators in natural marine ecosystems.  They seldom exceed 2.5 cm (1 inch) long, but there are a few bigger ones.  They are distinguished by the large scales protecting the dorsal portion of the worm.  If they are predatory, they may eat mostly small crustaceans.  The natural history of reef scale worms is poorly known, and they are rare in tanks.