A female Phronima sedentaria - ‘monster in a barrel’ - on Scilly today!
— Scott Reid (@stmarys_patch) October 23, 2023
An amphipod crustacean, she parasitises salps, devouring them from the inside, forming a vessel to raise her young!
These incredible creatures were the inspiration behind Ridley Scott’s 1979 film, Alien 👽 pic.twitter.com/4T27mzSAwP
Yes, it's horrifyingly accurate:
In order to construct their barrels, females first locate a suitable salp, pyrosome, or cnidarian host and either cut into the host or enter through an existing opening. Once inside, the female consumes the organism within and carve out the gelatinous inside, leaving nothing but the tunic.
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Female Phronima sedentaria are capable of producing up to 600 eggs at a time. Juveniles spend their early development within the mother in a specialized pouch called the marsupium. After finding a suitable host, the female begins to transform the barrel into a nursery for its young.
Here's more footage: