I did some research, as I'm 99% sure that is what they are and here is the info I've got. Copied from:
The only other large worm likely to be found in aquaria is the lysaretid polychaete Oenone fulgida. These animals are related the Eunicids, and, like them, possess jaws. They have three small antennae tucked in the groove between the two segments that make up the head, and a single dark eyespot may be visible on either side of the head.. Oenone fulgida has been reported to be circumtropical, and is quite variable for a single species. These studies date from the 1920s and it is quite likely that modern research, supplemented with genetic analyses, would show that what was thought to be one species eighty years ago is really several different species. The poorly studied nature of Oenone works against us, unfortunately, as it is relatively common in aquaria.
Whatever its status, animals that we presently refer to as Oenone fulgida may be easily recognized. As with the rest of the eunicid group, these worms lack the white tufts of setae characteristic of the fireworms. In fact these lysaretids tend to look relatively smooth, often without obvious appendages on their sides. This is an illusion, however, as they do have good appendages off of each side of each segment. The three antennae on the top of the head are small and often not visible, so the head looks smooth. In this particular case, color is a reasonably good characteristic to use in identification. Oenone individuals are typically orange, ranging from a dull, purplish orange to a brilliant blaze orange. They may be large worms, fully-grown adults often extend out of their burrows for two feet or more, and when fully extended they may be one quarter to one eighth of an inch in diameter. They typically live in burrows in rocks, but also may be found in tufts of algae or inside the water channels of large sponges. They are quite adept at detecting movement and will rapidly withdraw into their burrow if they are startled. Their withdrawal response, however, is not as rapid as that of Eunice individuals.
Oenone are nocturnal predators on snails and clams, and perhaps some other animals. They appear to extend from their burrow, and as they approach their prey they apparently secrete some mucus that covers the prey. This mucus may simply smother the prey, or it may contain some venom or narcotizing agent. After the prey is immobilized the worm extends a proboscis from the bottom of the head into the mucus and the jaws grasp the body of the prey. The jaws may also cut the attachments of the body to any shells, or alternatively the mucus may contain an agent that chemically severs the attachment. In any case, the prey's body is ingested. When the aquarist investigates the scene the next morning, all that typically remains is an empty snail or clam shell covered in a blob of mucus. Not many other predatory animals in marine aquaria typically leave behind such remains, consequently a dead, empty, shell covered with mucus is considered to be good evidence of the presence of an Oenone.
Figure 5 . This is the front end of a small individual of Oenone fulgida. Note the basic orange cast to the worm. This worm was about four inches long and about a quarter inch wide. A. Note the round "snout," or prostomium, and the three small tentacles at the top of the head. This configuration of snout and tentacles differs from the Eunice species (see Figure 4) and the fireworms (see Figures 1-3) and it is visible with a magnifying glass or hand lens. Note the relatively narrow segments as well; these make the worm appear smooth and lacking segments when viewed from a distance of about eight or ten inches. B. This is a lateral view of the head and front end of a preserved specimen. Note the proboscis is protruded from the mouth. These worms use the jaws located in the proboscis to grasp and manipulate food. C. This is a view of the head from directly above, showing the characteristic three tentacles. There is a single dark eye normally visible on each side of the head, but the eye pigments have faded in the preservative.
Oenone fulgida are not too hard to remove from a system, but it takes diligence. They most often live in burrows in rock, and enter aquaria in uncured rocks, and being nocturnal, the hobbyist has to search for them in the middle of the night. Using a red flashlight is best, as they will rapidly withdraw in the beam of a normal flashlight. They will appear as long worms stretched out and over the rocks. Once an Oenone individual is presumed to be living in a tank, the hobbyist must watch it withdraw in order to see where its burrow is found. After the rock with the burrow is located, the rock must be removed and the animal flushed from its burrow using a flood of carbonated water (soda pop works well). The worm is then discarded, and the rock replaced in the aquarium.
These things have been taking my snails out for some time now, I just figured the slime was them decomposing.......
