Bad hitchicker help

[Rnl]

Ok for the couple of days i have seen a empty green same shell on my live sand and couldn't figure out what it was . And today am looking at my clown fish and he has on one of his under body fins with like sucking sucking on him. Its like brown kinda like the size of a grain of salt .. Help please what can i do to get rid of it . Because i see a coup,emore little shells on the sand .same as the first one thank u in advance .

 

[Rnl]

Ok it kinda looks like a amphipod or copod it brown and looks to have a tranlucent tale i accually removed it from my fish but i still would like to know what it is cause i see a fell more empty shells on my sand

 

[Rnl]

Ok i figured out what it was . It was a celinoid isopod . Sorry i know that is not how its spelled . Now am just wondering if theres any more in my tank or did i get the only one. So far i haven't seen any more . Last night with a flash light and a piece of red cloth over it i was looking 4 more than an hour and nothing. Maybe in the clear????