Had a similar story... But with a damsel... This was my theory... The 2 damsels were fighting.... When I got home from work was going to take the meanie back to the LFS came home... he was missing.. Like you I searched every where... The only other thing in the tank at the time was that damsel... and within 2 hours between my boyfriend leaving and me coming home theres no way he ate him that quick.. AND would he of... I talked to my grandma and she said when one dies in her tank... the cats are quick to grab their expensive dinner... I do have a cat and figured she got em... Dont worry though I now have a better hood, I am sure it was dead anyways. Soooo point is, do you have a cat??? Might be a possibility....