4. Giant Siphonophore
This is a big transparent sea worm that you would expect to see coming out of an alien space ship. It looks like some sort of alien device and lives at depths of around 130 foot down. That is why it is transparent, since at that depth there are animals that can pick out changes in the darkness. It makes being transparent the best way of avoiding your predators. They live in pressures that are of 40 tonnes per square centimeter. If you capture one and try to bring it to the surface it will pop.