Wow, thanks for all the pics & comments, that's great! But (could you sense the "but" coming?) I have to cancel due to a family member's health problems. I was hoping that I could still fly up for the day which would be a really welcome break but I just can't leave. Hopefully we can reschedule for another time. Anyway, I figured I could at least comment on your pics here. Please keep in mind that my knowledge comes from field work, books, & reef boards. I don't keep tanks so any comments on reef-keeping are gleaned from the experience of others (like dealing with Montipora nudis).
Post #6 - Ibn's fireworm. This falls in to the Eurythoe complanata complex. The term complex means a group of species that look so much alike they're often mis-identified under a single name. In some cases it's impossible to separate them without genetic analysis, and since they usually have the same feeding mode trying to accurately identify them isn't necessary for a general discussion. This animal is a detritivore & scavenger. It is not a predator & won't go after healthy living animals. Normally it will eat detritus & some algae, if it's lucky enough to find a dead animal it will happily slurp away. Sometimes reefers will see them eating corals or other valued livestock. That means that the coral - which may have looked healthy really wasn't or was attacked by a true predator. Eurythoe has an excellent sensory system that allows it to scent necrotic or decaying tissue. It would have been attracted to the sick or lacerated tissue on the coral & true to it's nature start eating. It would be very interesting to see if Eurythoe acts like the maggots used by doctors to clean necrotic tissue due to gangrene or infected wounds. Once they've eaten all the necrotic flesh they stop & drop off (at least that's what I've read).
Post #7 - Ibn's Montipora-eating nudi. A lot of these predators are undescribed, especially these small cryptic ones. They are very difficult to eradicate. Nudibranchs are all hermaphrodites - simulataneous male & female. They don't do much in life except hunt for food, eat, and mate. When 2 individuals meet they pair up right side to right side so the genital openings are lined up, insert their penises, and exchange sperm. Both will then lay eggs. Some of them can retain viable sperm for quite a while after mating so a single one newly introduced into your aquarium can lay fertile eggs. It doesn't take long for juveniles to mature enough to mate. (I'm not giving specific times because it varies for each species & because it's unknown for most species) Life span is usually less than 1 year. These particular predators are tiny & often go undetected. The eggs ribbons are coiled & often laid in crevices or between polyps at the base of the colony so they're even harder to detect. Some reefers have reported eventual success stories but it requires taking the colony out of the main tank, constant observation, dipping, manual removal, for several weeks or even months. As the nudis may wander off the colony in search of food taking the infected colony out doesn't guarantee that the tank is free of them. They will starve to death without their specific food so if the infected colony is eventually free of them it can go back into the main tank if there aren't other, possibly infected Montipora in there.
Post #9 - JAR's hitchhiker. A female Homo sapiens, making it's way from one habitat/food source to another. Usually not found in reef tanks but still coveted by most male reefers. Treat carefully & above all wear a glove if direct contact is made as it may carry unknown parasites & diseases.
Post #11 - Gomer's hair worm -- Family Cirratulidae, likely to be in one of 3 genera - Cirratulus, Cirriformia, or Timarete. The common name spagetti worm has been applied to polychaete worms in this family & the family Terebellidae. Ron Shimek started called cirratulids hair worms. While I prefer scientific names (so much more accurate) I agree with Ron in having separate names for the 2 families. Terebellids are the mop-heads. All the feeding tentacles & branchiae (= gills) are located at the head. In cirratulids the feeding tentacles number 1-many pairs & are at the head end while the branchiae occur along the length of the body. Terebellids make real tubes for themselves. Cirratulids make pseudo-tubes - they use mucus & their branchiae to hold together loose aggregations of mucus & sand. Members of both families are detritivores, harmless, & useful members of the CUC.
Post #15 - Miles405 ?? - Either a sponge or a tunicate. I can't really tell from the photo. Touch it gently with a probe or a gloved finger. If the big opening closes quickly it's a tunicate. If it doesn't seem to close or closure is very slow it's a sponge. Both are filter feeders. The thing to remember about these groups is that like other sessile invertebrates they protect themselves against predator by producing spines and/or chemicals. Some are very toxic & will release those toxins if stressed or dying. Some are benign. I don't think there's much info on the reef boards about which belong in each category but most of the ones at LFS are probably benign.
Post #17 - Pixelpixi's Elysia ornata. Definitely an Elysia although I'm not sure about the species and it is an herbivore. Bill Rudman's Sea Slug Forum is an excellent - actually the best - source of information on all things sluggish. Once the food is used up it will die if it doesn't reach the end of it's limited life span first.
Post #20 - Mr. Ugly's rock. The dominant HHs are the yellowish ascidians (I think - again, try the touch test), white sponge, and vermetid snails. The vermetids are usually mistaken for polychaete tubeworms but they're snails that are too lazy to coil nicely like the rest of the gastropod community. They feed by producing mucus strings which collect floating particles, swallowing the nets back up, & digesting the particles. The large species grow slowly while small species - like the one here - reproduce rapidly. Essentially harmless, some reefers report that the nets bother their corals & keep them from opening fully. If you scrape or crush them eggs & sperm will be released to create the next generation so either take the rock out of your tank before manual removal or glue the openings shut.