Odo was so young it is hard to make any kind of call. Best case (and quite normal) is that she/he is holed up in the LR. Be sure you keep plenty of small crustacians (pods and hermits and you might try keeping some live shore shrimp in the tank). Worst case, she/he was so small that death did not disrupt the tank. Experience makes me tend toward the first guess. They typically stay hidden until around 5 months old.