Phronima sp.

Today's guest post is by Katie O'Dwyer, a PhD student currently at University of Otago in the Evolutionary and Ecological Parasitology research group. In one of my conference reports last year, I mentioned some of the research that she is currently conducting on parasitic flukes that live in periwinkles. She has provided us with a post about a parasite that she came across while walking along a beach in New Zealand.

Phronima and its salp barrel.
Photo by Katie O'Dwyer, used here with permission

After recently finding some salps containing the amphipod Phronima, washed up on a beach in New Zealand, I decided this was a worthy group to compose a blog about. It helped too that I was already interested in this group of crustaceans, having assisted with some work on them in Ireland. Read on for some interesting information on this little studied group of parasitic organisms…

Imagine a parasite which can create its own mobile nursery for its young, a parasite which is thought to be the inspiration behind the chestbusting xenomorph in the popular movie Alien. Well imagine no more! Introducing Phronima, the pram bug. These amphipods are members of the Phronimidae, a group of ten species of hyperiid amphipod, which occur in the water column throughout the open ocean. This sets them apart from their close relatives, which typically inhabit the benthic environment of the seafloor. So what has allowed this particular family to adapt to the pelagic or open water environment?

Those adorable little babies!
Photo by Katie O'Dwyer, used here with permission

Enter salps. What is a salp? Salps are gelatinous zooplankton which drift throughout our oceans. They may occur singly or in huge chains composed of individual salps linked together. Phronima is equipped with impressive front claws and with these they attach to an individual salp and carve away its insides until it forms a barrel. Phronima then climbs inside and sails the sea from inside a gelatinous barrel, collecting food from the water column. A number of questions may now come to mind regarding this symbiosis; has Phronima killed its host, which suggests that it is a parasitoid rather than a parasite, and why does it carry this barrel around as it must be pretty energetically expensive, right?

Well, as mentioned, these organisms live in the open ocean which presents several challenges to collecting samples for answering these questions. However, some dedicated researchers have indeed managed to study these fascinating creatures on the rare occasion that such an opportunity arises. From their research they have found that the salp in fact still contains live cells, although it hardly resembles a salp anymore with just a barrel of tissue remaining. The presence of live cells means that the barrel maintains its structure and that is important for Phronima to have a sturdy home. As the barrel barely resembles a live salp any longer, Phronima should really be considered as parasitoids rather than parasites.

Do a barrel roll!
Photo by Katie O'Dwyer, used here with permission

As for the energy involved in carrying around this barrel, the barrel provides a larger structure than the amphipod itself and this enables the Phronima to be more buoyant in the water column. However, some energy is still required to carry around this jelly barrel. Overall energy usage by Phronima is higher than that of benthic amphipods but on the lower spectrum compared with other pelagic or open water amphipods. This suggests that Phronima have indeed adapted to a unique niche which enables them to travel in the water column with their young and access new food resources without this behaviour being too energetically costly.

One unusual finding in the research thus far is that male Phronima are also found in barrels. If Phronima is known as the pram bug, which suggests the barrel is important for carrying offspring, then why should males carry a barrel too? Could they use it as part of some mating strategy, where they pass the barrel on to the female they mate with? Due to the difficulties associated with studying organisms that dwell in the open ocean many questions remain unanswered and this leaves us ever more curious and fascinated by creatures such as Phronima.

References:

Hirose, E., Aoki, M. N., & Nishikawa, J. (2005). Still alive? Fine structure of the barrels made by Phronima (Crustacea: Amphipoda). Journal of the Marine Biological Association of the United Kingdom 85: 1435-1439.

Bishop, R. E., & Geiger, S. P. (2006). Phronima energetics: is there a bonus to the barrel? Crustaceana 79: 1059-1070.

This post was written by Katie O'Dwyer.

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.