Help me ID 3 things, please!

[Matrfe]

Hello everyone! Great forum, so informative and so  thankful to be part of it!  Need assistance identifying 3 hitch hikers please. My tank is cycling (week 5). Since the beginning, I saw 5-6 sea stars that came in the live rock.  In the pic you can see one of the larger ones.  All 6 seem to be the same species... not sure if these will harm fish or not.  I don’t have any fish yet.   In the pic  you can also see a mantis shrimp (eating a piece of raw shrimp) this guy came out of the rocks on week 4.  He had been hiding since the beginning. Not sure if he is a spearer or puncher.   I’m concerned he will eat/harm the fish that I will soon add and or the other inverts I want to add. Finally, when I first got the live rock it had white patches on it.  You can see several in the pic.  These look soft but they are hard. Anyhow, just a few days ago, they started disintegrating.  Now they are like fruit pulp. I have no idea what they are/were or if I should leave alone or scrape off.   Any information or tips regarding these three “surprise guests” is greatly appreciated!! Thanks in advance! 

[jambon]

Looks like sponges on the rock.. the mantis being a smasher or a spearer will still be a problem when it gets hungry...

[Clown79]

The white stuff looks like sponge, the other is a baby brittle star.

 

Regardless if the mantis is a spearer  or smasher it will go after fish and inverts. Not about if but when. 

[Leo_ian]

I have one mantis hitchhiker. Ate 5 fish alrdy. get a trap to remove it

[Matrfe]

Thank you so much for your replies!! I greatly appreciate your time in helping me ID.  I’ll fish the mantis out!! 

[Clown79]

19 minutes ago, Matrfe said:

Thank you so much for your replies!! I greatly appreciate your time in helping me ID.  I’ll fish the mantis out!! 

you could make it a mantis dominant tank or start another one for the mantis. they are pretty awesome