Sand flea, they will dig into the sand and bury in. They really need a very mature sand bed. I never had much luck, but they need a colder water temp to survive, below 75. Prehistoric looking creatures, very cool. Be careful what you collect? A lot of stuff is invasive, especially if you see a lot of it, like Mussels. Don’t put Mussels in your tank, very invasive, and they only live 2 yrs. same goes for the Sand Flea, very short life span.