Tiny Little White Starfish and Some Sort of Snail

paulgriffin971 · Jul 31, 2022

So for about two weeks or so, I've seen a growing number of little critters starting to populate the glass of my tank. One is a pretty good amount of these little white starfish with a shorter leg on one side. The others are like a hard snail but about the size of a pea and shaped like an oval.

They never end up in the sump, but seem to come out during the late evening and stick around until about 9am the next day. Don't seem to be bothering anything, so figured I'd ask. Are these something I should be concerned about, or should I let them go? Seem to help keep the glass clean, but if they are a nuisance then I want to get them out now before its too late. If they are a problem, is there anything--fish, crab, etc that will eat them? Or, am I looking at a chemical solution if they are in fact bad?

paulgriffin971 · Jul 31, 2022

Sorry, forgot the pictures:

PR_nano · Jul 31, 2022

Asterina starfish, folks have mix opinions, some say they are good some say they eat zoas.

ISpeakForTheSeas · Jul 31, 2022

Yeah, asterina starfish (technically Aquilonastra, but known in the hobby as Asterina). Personally, I like them, but they do reproduce quickly (very quickly), and some people believe they eat corals (see my quotes below).

ISpeakForTheSeas said:
With regards to whether or not they eat corals, it might be a species specific thing, it might be a you have way too many starfish so they're out of other food options thing, or it might be they're eating the slime coat/mucus on the coral rather than the coral itself (see below).

The quote I referred to in my quote above:

Timfish said:
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.

The snails are limpets - possibly Keyhole Limpets but I can’t tell for sure.

There’s some speculation about Keyhole Limpets possibly eating SPS corals (see below), but most limpets are confirmedly beneficial:
If yours is a keyhole limpet, I don't know that anyone has actually confirmed that they eat SPS (much like how people believe "Asterinas" - actually Aquilonstra - stars might eat their corals: they might, they might not, it might be species dependent or food availability dependent, it might be they're eating the slime coat/microalgae growing on the coral and actually helping the coral, it might be they're eating only unhealthy corals, etc. - we don't know for sure).

Keyhole limpets are fairly easy to identify by the "Keyhole" at the pinnacle of their shells (it basically looks like they have peephole/bullet hole at the top, typically in/near the center of their shell). So, you should be able to tell relatively easily if that's what you have.

SaltyT · Jul 31, 2022

^ agree asterina starfish and the other things are limpet snails.

You can get a harlequin shrimp to eat your asterinas if you want to get rid of them, but once it eats all of the stars you'll either have to rehome it to another reefer or give it back to the LFS. Harlequins only eat starfish they'll starve once they eat them all - or you can feed chopped up chocolate chip starfish to them, but most folks don't like doing that.

The limpets are a good part of your CUC, but they can occasionally get caught in power heads.

paulgriffin971 · Aug 1, 2022

Thanks everyone. I tend to jsut manually remove the few that I can get to on the glass in the morning, and nothing seems to be bothered so I guess I'll just keep an idea on them. I will say my glass is a lot cleaner from them being in there, was jsut worried if they would ruin anything pricey in the tank---which I definitely don;t want