#some relationships between phronima and tunicates are arguably symbiotic

[ocean-sunfish-hater]

Parasitoidism and Deep Sea Mechs

ID: A white/ transluscent crustacean inside of a barrel-like jelly structure that is transparent. They are set against a black background.

This shrimp-like creature is a type of deep sea amphipod called Phronima, referred affectionately by some as a barrel bug. Look! It's got a little house for itself! How did it get there? Why is it doing that? Oh god, what does this have to do with the title of this post?

Parasitoidism is an extreme form of parasitism where the host will eventually die. This is different from the other types of parasitism where there may be detriments to the host, but they rarely die as a direct result of the parasitism. Think of a flea - they might suck their host's blood and they may cause damage to it, but one flea will never suck so much blood as to kill the host (of course, it may later die of a disease transmitted by the flea). For a parasite killing the host isn't the best strategy, because then you are essentially destroying your home, your restaurant and your social life all at the same time.

ID: An orange parasitoid wasp sits on top of a bristly caterpillar, with its sting buried inside its victim. They are both sat on a leaf, and the picture is taken close up so that the finer veins of the leaf are visible.

Parasitoidism, on the other hand, eventually results in the death of the host due to the extreme amount of resources taken from it. Most famously, parasitoid wasps lay eggs inside a paralysed host, keeping it alive long enough for its offspring to hatch and consume it. Some larvae even eat non-essential organs first to keep their hosts alive for as long as possible as they grow. Apparently Charles Darwin thought this was so fucked up he questioned whether his God was truly omnipotent or benevolent if such a creature existed.

ID: A picture of a sea salp, a type of marine invertebrate. It has a transparent, jelly-like body that is somewhat tube shaped. Inside the body are two major structures: an orange, spherical mass to the right hand end, and an opaque, white rod-like structure that runs along the body (right to left in the picture). It is set against a dark background.

Anyway, that jelly-like structure that the Phronima is sitting in, it's not something that it made itself through some bodily secretion or scavenging. It's actually the hollowed-out body of an animal called a salp, which is a type of tunicate (these can sometimes form massive colonies, hopefully have a post coming about that at some point).

The Phronima eats the inside of the salp then climbs inside the remaining tunic, in which it makes its home and lays its eggs. It then proceeds to pilot the carcass around like a fucking mech, steering it through the deep sea. Moving its new mobile home round like this allows fresh water and food to flow in through the front, nourishing the happy new homeowner and eventually its larvae once they hatch.

Of course, at this point the salp is likely dead and has been for a while, which is what makes this parasitoidism.

Hope you enjoyed! Have excellent nightmares.