If you spend your days cruising the world’s oceans, safely tucked inside a submarine you carved from the body of one of your victims, chances are you’re a Phronima parasite. With their large claws and bulbous head crests, the planktonic crustaceans look like H.R. Giger himself drew them into existence. Will the real Xenomorph queen please stand up?
Source: Katie O’Dwyer, The Conversation. Repurposed by Creative Commons
The animals look so classically Alien in fact, fandom has long-perpetuated the rumor that Giger used them as inspiration for his characters. Even Sir David Attenborough made the claim in the 2001 BBC series The Blue Planet. According to Giger’s once-agent, Bijan Aalam, this is more fiction than fact. “Geiger never inspired himself by any animals, terrestrial or marine,” he explains, but that doesn’t make the story any less cool. If something as iconic to science fiction as Giger’s alien has been hiding in the deep-sea all along, imagine what other fictional creatures could have real-life counterparts – just waiting to be discovered.
Unlike the queen Xenomorph’s, Phronima’s head crest is actually a second set of eyes. (Yes, you read that right. This animal has four eyes.) Being a parasite in the deep-sea has its challenges, namely, finding a host in a space where light is a hot commodity. While one set of Phronima‘s eyes point down, a second set of tubular eyes points upward to catch any rays that trickle down through the water column. Because they can see in extremely low light, the parasites are able detect the silhouettes of potential host animals, like jellyfish and salps (gelatinous tunicates like the one you see below), against the black backdrop of the deep.
After latching on, the squatters use their sharp claws to cut and eat their prey’s innards, saving the gelatinous exterior for use as a mobile home. Interestingly, the animals seem to know when to stop cutting in order to keep the host in a partially-living state.
“Studies of salps that have been hollowed out by Phronima show that they still contain live cells,” explains parasite researcher Katie O’Dwyer. “This helps the barrel maintain its structure and gives the Phronima a sturdy home. But the hollowed out salp barrels hardly resemble a living salp, with just the tissue remaining. This being the case, Phronima should really be considered as a parasitoid rather than a parasite.” As it grows, the parasitoid builds bigger, and bigger barrels, even going so far as cutting and reassembling panels of flesh to create the right shape.
Source: NOAA Fisheries West Coast/Flickr
Enter the next phase: chest bursting. Unlike many crustaceans, the female Phronima takes care of her eggs, which she lays within the walls of the barrel. She’ll protect the embryos as they feed and grow, using the host-body like some kind of Proteus-spawned Baby Bjorn. The strategy has led to the animals’ common name, “the pram bug.” (That’s stroller for all you American-English speakers out there). Like their Alien counterparts, the young eventually wriggle out of the host-body, setting off to find their own.
“Although the barrel provides a safe home for Phronima’s offspring, the male pram bugs carry a barrel too,” adds O’Dwyer. “Maybe it helps to have a superior barrel when finding mates, we currently don’t know. Such unknowns leave us ever more curious about this difficult to study, open-ocean dwelling, creature.”