Ughhhh i hsbe yet to find a hitchhiker idk what heck it is. I have a 75g 20g sump very few coral, only have 2 clownfish and 2 goby i think. The tank just hit a year old
Limpet, chiton, or even possibly a stomatella snail. Without a pic of the top, no way to tell for sure. Either way it's a good guy and should be left alone.
It is a Limpet. Chiton has 8 segment shell. Stomatella snail is a snail with single shell but body extend beyong the shell. Limpet has shell that is like a Vocano. soft body that is completely under this very strong shell. They will do fine exposed to air for long periord of time, hours.