brittle star behaviour

[i have crabs]

last night (full moon) i looked in my tank wich just had moon lights on and seen my brittle star (about 10") out on the sand close to the glass. wich i thought was strange since it always stays under the rocks and never goes out in the open,so i was watching for a minuite and it started climbing the glass went up the whole 28" and then crossed the tank about 2-1/2 feet sideways,i didnt even know brittles could let alone why it would do this,any ideas on what it was up to?