Yeah, our tanks generally aren't designed to handle starfish since most of them either eat corals or biofilms (or both). Most people go with small serpent or brittle stars (again, not the large green variety, they prey on sleeping fish). Personally, I like Aquilonastra stars (typically called Asterina stars on the forums here), but they're tiny (less than an inch in diameter) and reproduce to the point where many people consider them pests. Some people think they eat corals, but there is some evidence to suggest that they only eat the microorganism filled slime produced by corals (and they may in fact be beneficial to the coral as a result). If they do eat corals, it would likely either be a "specific species eat it" thing or a "there are too many starfish in your tank and they are starving so coral is the only option left" thing.
It's an Aquilonastra spp. starfish and is a great scavenger. I see them with anywhere from 4 to 12 legs. The whole discusion around them seems to me excellent examples of misidentification, mistaken behaviour and assumed causality based just on heresay without looking at the research. Asterina spp starfish are preditary but only reproduce sexually and are shortlived so while it's possible some might get into a tank even if it did happen it's not going to be around long.
Aquilonastra are one of the uncommon species that reproduce fissiparous or by splitting so are easy to identify by the different sized legs regrown after splitting. They perform an important function not only feeding off algae films but also feeding off microbial films including those on corals (at least ones that don't sting). FYI the mucus coating on corals ages and corals have to periodicely shed it to renew it and maintian healthy microbial processes (
Ref 1,
Ref 2). If Aquilonastra are feeding on zoas or softies I'll argue they are either benign or even beneficial as they may be reducing the unhealthy older mucus which can be full of unhealthy microbes which the animal is trying to get rid of and are far more likely to be the actual problem.
Here's an example, this Toadstool is doing one of it's periodic sheddings. The Aquilonastra have been in this system for years but only climb onto the Toadstool when it's shedding. In the first picture you can see the old mucus film, Aquilonastra starfish and areas they have cleaned off. The second picture shows the Toadstool a week later.
Those are your best options for your tank that I'm aware of currently. If you were running a coldwater tank, I might have better suggestions, but for a 60 cube tropical reef tank I don't know that there really is a better option.
If you really want to, you can try
Phataria unifascialis, but the only person I know of who has kept one mentioned that it ate their zoanthids, so there's a decent chance it would develop a taste for at least some corals after a while (zoas seem to be just about every coral eaters favorite though). Otherwise, your best bet would be the much less cool looking sand sifting starfish,
Astropecten polyacanthus. That said, a sand sifting star would be pretty large for your tank since they get up to ~10-12 inches in diameter. Regardless, if you're interested in trying the sand sifting star, here's some of the relevant information which may or may not be helpful (in theory it should, in practice, who knows):
With sand sifting stars, most people recommend waiting until your tank is established before adding them - however, you might be able to target feed it with things like clam on half shell, oyster, snail or conch meat (a lot of places offer these frozen), a good quality omnivore food (like LRS Reef Frenzy) etc. It should swallow any of these foods whole, as long as the food isn’t too big for the star. They generally feed on detritus in our tanks, but target feeding might provide enough of the proper nutrition for them, and these are supposed to be some of the kinds of food they eat in the wild anyway. Plus, they are known for eating all of the detritus in our tanks and starving to death, so target feeding them larger food pieces relatively regularly might actually help it do better long term. No guarantees though.
If you decide to get it and try target feeding it, let us know how it turns out.
Mussel and whelk could potentially be fed as well, but with the mussel I've heard that clams may be more nutritious.
TLDR; Small serpent or brittle stars (not the big green ones), micro brittle stars, and Asterina (Aquilonastra) stars are the safest choices. If you're feeling daring you can try
Phataria unifascialis, but it might eat your corals, or you can stuff a sand sifting star in your tank and try target feeding it specific foods with no guarantees it won't starve.
Hope this helps - sorry I can't offer a better option!
