Look at this amphipod: it's both a ruthless killer and and, in some ways, an "alien".
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Phronima sedentaria is a deep sea parasitoid.
Instead of constantly feeding on a live host like a parasite, females attack salps, pyrosomes, and cnidarians.
Once inside, the female consumes the organism within and carve out the gelatinous inside, leaving nothing but the tunic, laying their eggs inside. They are capable of producing up to 600 eggs at a time. The prey becomes a nursery for its young.
Then it propels the barrel as the larvae develop using their strong pleopods until the young are developed and they are able to restart the cycle independently.
Apart from being a kind of "alien" creature itself, it also influenced the design of the queen alien morph, seen in “Aliens” (1986).
[📹 Scott Reid / stmarys_patch]