Not an asterina starfish?

[jpark457]

This little guy came as a hitch hiker on a small live rock I recently got from another reefer. Doesn’t look like an asterina to me. I think he’s kind of cool but wanted to see what people think re an ID and reef safety. Same rock had a pistol shrimp burrowed inside!

 

[monkeyCmonkeyDo]

Asternia
D

 

[jpark457]

It’s a lot bigger than the asterinas I have already in the tank, like May be even 3 times the size and in person has kind of a blue ish color. I guess there are several species of asterina…

 

[ISpeakForTheSeas]

I agree that it's likely some kind of "Asterina" starfish (technically Aquilonastra, but known in the hobby as Asterina).

I'd also say to keep it though (but that's just me).

It depends on the species - some of them can get up to almost 4" (~10cm). Most common ones in the hobby are tiny, but there are actually a number of Aquilonastra species that get larger than 2cm.

Just to add some info on these stars to the discussion (pasted from another of my posts):

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.