Serpent starfish come in a few different colors and styles, and all of them are a good choice as part of your cleanup crew. They will retreat into the rockwork most of the time, but surely will be seen when food hits the water. This banded starfish has been with me for more than six years. I have a pair of tan-brown ones since 2004, so 14 years at the time of this entry. They don't prey on fish or other invertebrates, and help keep the surface sand devoid of waste. I'd recommend one in a 30-60g tank.
Even though they aren't always visible, Serpent Starfish are quite active and keep the rockwork clean of any detritus. During feeding time, their arms can be seen waving from nooks in the rocks, as they hope to catch floating bits of food. They can be target fed with a piece of shrimp, but it seems to be unnecessary. You can find them in different colors, some have stripes or other markings. Reef-safe.
Late at night, I saw these tiny worms darting through the water. In the six years I'd been a hobbyist, I'd never seen this occur and was fascinated. They seemed to be attracted to the light of my flashlight. You can see two worms in the picture above, next to a Nassarius snail. They are about the size of a small maggot. I was later told this is the spawning pattern of several different types of polychaete worms. Please read the discussion and view more images.
Another color from the Linkia starfish family, adding a real splash of orange in your reef. Reef-safe
The green Brittle Starfish is sold to newer hobbyists as an active specimen, but they aren't warned how predatory it can be. Excited by the smell of food in the water, this animated echinoderm will cruise the tank looking for its next meal, but that speed also puts other fish at risk of becoming prey. If this animal is target fed often, it may be kept with others in a reef tank, but most people would not recommend this as reef-worthy including myself. Not Reef Safe.
Green Brittle Starfish are very active when they sense food in the water, and move excitedly with decisive swiftness. They can grow quite large, easily 18" from tip to tip. They can eat fish or crabs that stray too closely. While direct feeding may avert losses, eventually nature will take its course. It is beautiful, but save yourself the heartache as it is Not Reef-safe.
It takes a keen eye during late night hours to notice this particular creature. The first one I ever saw was in my refugium, and was a little thicker than a hair and about 1.5" in length when fully extended. If you watch Digitate hydroids for any length of time, you'll realize this is a thinking creature that is filter feeding similar to Fly Fishing. The fuzzy end will sway in the current, and the worm will reel it in in short jerks, only to release it again. It is extremely dilicate in nature, and interesting to observe.
Bristleworms are blamed for everything negative that occurs in reef tanks, but they are actually very good clean up detrivores. Count on them to find excess food missed by your fish, and expect to see many of them at night with a flashlight. They are often found on decaying matter, and thus are blamed for the death of the [insert creature here] rather than praised for keeping the tank clean. Reef-safe! Here is an extra image with a few larger ones.
Late at night, I saw this strange creature stretched out across the substrate. It looks like a plant, but this is actually the proboscis of a Bonellid Echiuran Worm. I've never seen the body of the worm, but the tendril will reach out quite far. In this shot it was out at least 12" from the source in the rockwork. According to Dr Ron Shimek, it is a harmless detrivore. If you want to see one in your tank, look while the lights are off, using a dim flashlight. As soon as light is sense, it pulls back in quickly.
The Biscuit Starfish (Pentagonaster duebeni) is a neat discovery that Mitchell found in his live rock when setting up his tank. It hitched a ride into the aquarium, and survived without proper acclimation since it was unseen. It's normal diet is sponges, bryozoans and sea squirts, so keeping it fed may prove difficult but it will graze on live rock. The more live rock, the better. This species can be found from the warmer waters of Western Australia all the way to Queensland.