Choniomyzon inflatus

Photo of C. inflatus from the paper

I guess you could say that the parasite we are featuring today is a "balloon animal" and indeed its name refers to that property. According to the paper that described and named this copepod - Choniomyzon inflatus - "The specific name of the new species is a reference to its swollen prosome, which resembles a balloon."

But you won't be finding this odd little crustacean at any kid's party, instead it is usually attached to the egg masses of smooth fan lobsters (Ibacus novemdentatus) on the coast of western Japan. It is the third species from the genus Choniomyzon to have ever been described. The other two known species are C. panuliri, which are found on spiny lobsters from India, the British Solomon Islands and the Great Barrier Reef, and C. libiniae, which live on spider crabs from São Sebastião Island, Brazil. All three species attach themselves to the external eggs masses of their respective hosts.

SEM photo of C.inflatus
from the paper

So why do they look like a miniature hopper ball toy? Well, that relates to where they live and what they feed on. Chioniomyzon inflatus belongs to a family of copepods called the Nicothoidae and the reason they do this Humpty Dumpty impersonation is so that they can insinuate themselves amidst the eggs masses of larger crustaceans.

Normally the host crustaceans would remove any foreign particles or organisms that get caught up in their brood pouch or egg mass, but by disguising themselves as an egg, C. inflatus and their relatives can stay there undisturbed. And while the appearance seems comical to us, it is seriously bad news for its host because nicothoid copepods are egg-eaters - they have a syringe-like mouthpart with which they puncture their host's eggs and suck out their contents.

So C. inflatus masquerades as just another egg in the brood to avoid being expelled meanwhile munching on the actual eggs around it. This strategy is rather reminiscent of another creature that we featured during the first year of the Parasite of the Day blog - the cuckoo catfish which hides its eggs amongst that of mouth-brooding cichlids. You can read more about the cuckoo catfish here.

Reference:
Wakabayashi, K., Otake, S., Tanaka, Y., & Nagasawa, K. (2013). Choniomyzon inflatus n. sp.(Crustacea: Copepoda: Nicothoidae) associated with Ibacus novemdentatus (Crustacea: Decapoda: Scyllaridae) from Japanese waters. Systematic parasitology 84: 157-165.