I found this section of an article the most helpful so far for those who are interested.
Eunicid worms are formidably complex animals. They are described as having an eversible pharynx, meaning they have an extensible tube that projects outward from the mouth. This tube is armed with two to five pairs of large forceps or pincher-type lateral jaws and one pair of additional jaws that are ventrally situated. This group contains the largest polychaete worms. There are some reliable reports of eunicid worms being an inch in diameter and fifty feet long, although the largest
confirmedspecimens are smaller. Specimens in excess of six feet long are common in nature, and occasionally such giants are found in marine aquaria. They are also long-lived. I have had one for several years now; transferring it from tank to tank during remodels and revisions of my system.
The eunicid worms found in aquaria all have five antennae, with a large pronounced antennae arising from the center of the "forehead." Large eunicid worms from two distinct groups are found in aquaria. Both enter the tanks hidden in live rock. The most distinctive of these are worms in the genus
Palola. These are rock-inhabiting worms that reach lengths of three to six feet. They are generally dark green to blue to black and are largely nocturnal. They will extend from rocks to feed and appear to be mostly scavengers or detritivores. However, little is known about their diets in nature, and if any are found in aquaria, they may well be able to eat small fish or shrimp. On the other hand, there is no hard data that they do so.
Palola is a genus whose synchronous spawning is legendary. Prior to such spawning events, the rear portions of the animals are filled with eggs and sperm and, when the time is right, they spawn. The spawning cues appear to be lunar and tidally influenced, but whatever the trigger, most of the worms in large geographical areas spawn within a few minutes. The rear portion of the worm separates from the front portion and swims to the surface where it writhes around and ruptures. With millions of worms spawning at once, the sea literally becomes covered in a wriggling mass of large worm fragments. It is thought that mass spawnings of this nature occur because although predators will be attracted to such spawns to eat the worms and their gametes, there will be so many animals spawning that the predators get sated, and many of the eggs escape to become fertilized, and undergo development into juveniles.
Palola worms are probably harmless in most reef tanks, but if one does spawn, it may produce enough gametes to seriously foul the tank. They are often found dead or dying in uncured live rock.
Worms in the genus
Eunice, sometimes called "bobbit" worms are, if anything, more impressive than their
Palola cousins.
Euniceis a large genus, with well over 150 species, and it is hard to generalize about them. As with the
Palola, they have five antennae, including one in the center of the forehead and they all have jaws, in some cases wicked, scimitar shaped hooks with accessory spines and hooks. These are not jaws for chewing the prey or food item, but rather are jaws designed to ensure the food that, once seized, never gets away. Some of these worms get very large; the largest I have seen reported from reef tanks was in excess of 6 feet long, and individuals of
Eunice aphroditois may be much larger.
Eunice individuals tend to live in mucus-lined borrows in rock or sediments and may have several entrances to their tubes. Two distinct kinds of worms seem to be represented in this genus. One kind, which is benign in reef tanks, seems to be mostly scavenging its food. It lives in a burrow in the sediment, or more rarely, in a burrow in the rocks. When feeding, one of these worms will slowly extend from its burrow. They typically have four to six eyes and are quite capable of detecting motion outside the aquarium, and across the room. It will slowly search the surrounding area for food and if bothered by a fish, or its own shadow, will retract into its burrow with a velocity that has to be seen to be believed. Contraction back into a burrow has been clocked in excess of 20 feet per second, and if only a couple of feet of the worm are visible while it is foraging, that worm can disappear, quite literally, in the blink of an eye.
Figure 4. This is "Max," the large
Eunice individual that I have had in my aquaria for about five years.
A. The head, note the characteristic five head tentacles from the head, and specifically note the one arising directly from the center of the "fore head." The worm is about half an inch across. Note the complete lack of visible setae or bristles; eunicids do not have the white protective bristles found in fireworms, and they often keep their other bristles withdrawn.
B. In August of 2002, I had to move Max from one tank to another, and he broke into three fragments. His total length was over four feet long. He has recovered from this and is living in my present tank. He is shorter, but I anticipate he will grow to his former length.
C.Note the gills and compare them to the ones on
Eurythoe in Figure 1.
All of the large
Eunice individuals that I have heard about in reef aquaria seem to be scavengers. However, the largest
Euniceindividuals seen in nature are impressive predators. Individuals have been reported to strike upward from the sediment surface, grab a four-inch long fish swimming above the sediment, pull it under the sediment and presumably snack on it at its leisure. Such worms are also reported to be an inch in diameter and about thirty to fifty feet long, making them a bit larger than most home aquaria could accommodate.
There are also smaller species of
Eunice, and these seem to be reported from time to time in aquaria. They generally appear to be harmless scavengers, however, even I, a self-proclaimed vermophile, would consider them amongst the "usual suspects" if some small fish such as fire fish or small gobies disappeared without a trace.
Regardless of the size of its individuals, the major characters for identification for the identification of eunicid species would be the absence of white tufts of setae, and the presence of five large and visible antennae (large relative to the worm, not the aquarist), such antennae are typically about two to three body diameters in length. Colors are secondary characters with these animals, but the
Palola worms are often dark colors, while the
Eunice individuals are, typically, shades of brown
