Presenting the Mantis Shrimp:



Highly carnivorous, highly intelligent shrimp like creatures that end up in seawater aquariums as stowaways when buying 'living' stones (e.g. stones with sea life on it). Best indication that you have one in your aquarium is when all of your expensive fish start disappearing one after the other. And to add to the fun they also make a characteristic popping sound with their pincher's, resembling the sound of breaking glass. And it is strong enough to back this threat up, breaking through the aquarium glass if it wants to.

So not only will it cost your a fortune in livestock, it will also make you fear water damage to your furniture. Of course there are always people who keep these things as pets.

Not convinced that its a Cestum veneris, they seem more ribbon like and this was definitely tubular.