Check out this ruthless deep-sea predator: Phronima sedentaria.
Unlike typical parasites that feed continuously on a living host, this amphipod is a parasitoid. Females attack salps, pyrosomes, and cnidarians, hollowing them out from the inside. They consume the soft tissues, leaving behind the gelatinous tunic as a makeshift nursery.
Each female can lay up to 600 eggs inside this "barrel," using it as both shelter and transport. By beating their powerful pleopods, they propel the structure through the water until the larvae are fully developed and ready to continue the cycle on their own.
With its eerie life cycle and alien-like appearance, Phronima even inspired the design of the Xenomorph Queen in Aliens (1986).
[📹 bobtec]