Something lurking in the darkness

[JaiWiz]

Howdy folks,

Over the past 6 months i have lost a very big(4") and beautiful coral banded shrimp and just recently a 12" red sea star. The weird thing is there was no remains of either critter i have not lost any fish i think but i havent seen my lawn mower blenny for awhile either. My tank is a year and a half old all parameters are good nitrates sometimes get up there but not to the point of making things disappear. So i'm wondering if some how i got a mantis shrimp in there who is growing and is now able to eat things of a decent size someone please tell me some other ways to find out if you have a mantis hangin out in the rocks. Or any suggestions on what could be happening.