August 10 - Dicrocoelium dendriticum

Dicrocoelium dendriticum, better known as the lancet fluke, is a species of fluke that lives in the liver of grazing mammals such as sheep. Like most flukes, it has a 3 host life-cycle, the adult worm living inside the sheep, lay eggs which are shed into the environment with the sheep's faeces. The first intermediate host for this parasite are terrestrial snails which become infected by accidentally ingesting the parasite's eggs. The parasite undergoes clonal replication inside the snail, producing hundreds of infective larvae which are then packaged into slime balls and extruded into the environment. For some reason, these slimeballs are eagerly gobbled up by ants which are the parasite's second intermediate host.

Now sheep are not known for including ants as a significant part of their diet, so how is D. dendriticum supposed to get itself into a sheep through an ant? It does that by taking control and setting its ant host up for a rendezvous every evening. Once infected, the ant begins to behave very oddly indeed. As dusk falls, it would crawl up a blade of grass until it reaches the tip, then firmly clamps itself into that position with its mandible for the entire evening. The infected ant would perform this peculiar routine every night, but as the sun rises, it would resume its usual activities - assuming that it has survived the evening and not been incidentally ingested by a hungry sheep. By inducing this peculiar behavioural pattern in the ant host, D. dendriticum brings itself (through the ant) within the vicinity of a grazing sheep, thus setting up an encounter which otherwise would not have occurred, allowing it to complete its seemingly obtruse life-cycle.

Check out the very funny cartoon version of this life cycle here.

Contributed by Tommy Leung and thanks to Craig Carlough (Lancaster, PA) for sending along the Oatmeal comic.

August 9 - Schistocephalus solidus

Schistocephalus solidus is a tapeworm with a three-host life cycle. Free-swimming coracidia are eaten by copepods, the first host. After about 2 weeks of development in copepods, the worm is ready to be transmitted to the second intermediate host, three-spined sticklebacks. In the fish host, the worm grows to gargantuan sizes; in exceptional cases it can even weigh more than the host. Fish are impacted in various ways by infection, showing altered behaviours (risk-taking, flight response, etc.), brain chemistry, and immune responses. These modifications are thought to lead to a higher transmission rate of the parasite to its final host, fish-eating birds. Within 48 hrs of reaching the intestine of the final host, the parasite is reproductively mature and producing eggs. After about a week, the worm has produced all its eggs and dies. This short and explosive reproductive period is presumably the reason why S. solidus is one of the few helminths that can be bred in vitro.

Contributed by Daniel Benesh.

August 8 - Nybelinia surmenicola

Nybelinia surmenicola is another tapeworm parasite that infects the salmon shark, Lamna ditropis. The sharks get these parasites when they prey on either fish or squid that are serving as the intermediate hosts for this parasite. Salmon sharks are interesting creatures, themselves, in that they one of the few fishes that exhibit homeothermy, or the ability to regulate their own body temperature. These sharks live in the northern Pacific ocean. At least one case of a human infection of Nybelinia surmenicola has been reported. A Japanese woman complained of severe pain in her mouth after eating uncooked squid. Doctors removed four larval tapeworms from her tongue and pharynx.

August 7 - Caligus oculicola

The parasite Ommatokoita elongata probably made a few of you squeamish. If so, then you probably want to just close this page, too. Caligus oculicola is a recently described species of copepod that lives on the surface of the eye of tiger sharks (Galeocerdo cuvier). Although most species of Caligus infect teleost (bony) fish, not sharks, this copepod seems to have found an ideal habitat of the eyes. They have specialized structures that allow them to adhere, suction-cup style, to the eye and then they proceed to feed on the host's tissue through a scraping and swallowing kind of fashion.

Drawing of a male Caligus oculicola, modified from the original paper.

Thanks to Laurence Frabotta and Colleen Ingram for nominating this parasite.

August 6 - Paronatrema sp.

On the whole, digenean trematodes aren’t very common in sharks. Parasitologists learn early that tapeworms rule the sharks, and trematodes rule the fishes. There are a few exceptions, like the giant flat gorgoderids that live in the body cavities of sting rays, and today’s parasite, Paronatrema, which is a member of a very poorly known group called the syncoeliids. Paronatrema and the only syncoeliid that infects sharks – Otiotrema – are unusual in another way: they are ectoparasites. Nearly ALL trematodes are endoparasites; even the ones that live on the skin (e.g. Transversotrematids) are technically endoparasites because they are under the first layer of skin. Not syncoeliids; these are bold enough to choose a totally different host group and to live free and open on the surfaces of the gills and branchial cavity of sharks. How do they do this? No one really knows, because they have hardly been studied at all. Given that you have to put your hand in a tiger shark’s mouth to get one, perhaps its no surprise…

Contributed by Al Dove.

August 5 - Dinemoleus indeprensus

Dinemoleus indeprensus is a parasitic copepod which is in the same family as Pandarus rhincodonicus (the whale shark ectoparasite), however there is something that sets this little guy apart from the rest. For obvious reasons, parasite fauna are usually described only after their host species are recognised - but not this one. D. indeprensus is an ectoparasite of the Megamouth Shark (Megachasma pelagios), and it is notable for being probably the only parasite to have been formally described before its host. Due to some unusual reasons, while D. indeprensus was already described in 1978, the Megamouth itself was not officially described until five years later in 1983!

The description for D. indeprensus is here:
Cressey, R., Boyle, H. (1978) A new genus and species of parasitic copepod (Pandaridae) from a unique new shark. Pacific Science 32:25-30, which is also where the picture came from - check out the intro of that paper!

Contributed by Tommy Leung.

August 4 - Pandarus rhincodonicus

The host for today's parasite is the mighty whale shark (Rhincodon typus). Pandarus rhincodonicus is parasitic copepod which lives on the skin of the whale shark and are frequently found on the leading edge of the shark's lips and fins. As you can imagine, this is not an easy place to make a living, as the whale shark swim at a speed of about half a metre (almost 2 feet) per second, the drag forces on P. rhincodonicus is substantial. However, the copepod's streamlined shape minimises drag forces, while a series of adhesion pads and hooks allow it to cling tightly to the whale shark's skin. The edge of the carapace is also fringed, which may also help generate a vacuum which press the copepod firmly down upon the skin, acting like a living suction pad.

The photo is a dorsal and ventral view of a female copepod and it came from this paper:

Norman, B.M., Newbound, D.R., Knott, B. (2000) A new species of Pandaridae (Copepoda), from the whale shark Rhincodon typus (Smith)' Journal of Natural History 34:355-366.

Contributed by Tommy Leung.

August 3 -Branchotenthes robinoverstreeti

Guitarfish are really rays, not sharks, but they're closely related and some species are also called sand sharks, so thought this one could slide as a "Shark Week" parasite. Besides, the irony of this parasite is just too much to pass up. Branchotenthes robinoverstreeti is a recently discovered monogenean parasite that infects the gills of guitarfish in the Indian ocean. The haptors of B. robinoverstreeti, which are the posterior structures used to attach to their hosts, look strikingly like the head of a guitar with the six tuning keys. The parasite was named after Dr. Robin Overstreet, an eminent parasitologist of the Gulf Coast Marine Laboratory.

Image is from the original paper.

August 2 - Gnathia trimaculata

TThe parasite for today is a parasitic isopod belonging to the family Gnathiidae - the larvae of this particular species feed upon the requiem shark (Carcharinus melanopterus). There are many different species of gnathiids parasitising many different species of fish, and they have an interesting life-cycle which involve "protelian parasitism" where only the juvenile stages (called a praniza) are parasitic, while the adult stages are free-living. They go through several stages of development, alternating between feeding and non-feeding developing stages (when they are engorged with blood) before reaching sexual maturity.

They are almost like a functional equivalent of ticks for fishes - they wait in ambush for a passing host, and when one arrives, it climbs onboard, sucks blood for a few days until full, then drops off to develop into the next stage. And like ticks, they can also act as vectors which can transmit blood parasites between the fishes they feed upon.

The photo shows a pair of third-stage pranizae, scale bar is 1 mm and it came from this paper:

Coetzee, M.L., Smit, N.J., Grutter, A.S., Davies, A.J. (2009) Gnathia trimaculata n. sp. (Crustacea: Isopoda: Gnathiidae), an ectoparasite found parasitising requiem sharks from off Lizard Island, Great Barrier Reef, Australia. Systematic Parasitology 79:97-112


Contributed by Tommy Leung.

August 1 - Anthobothrium sp.

Sharks are predators, usually thought of as at the top of the food chain in ocean ecosystems. As such, they can accumulate a lot of poisons or toxins, as we have seen recently in the news with scares of mercury in tuna. But it turns out that some of their parasites can be accumulating the toxins in extremely high concentrations and there is speculation that in doing so, they may be protecting their hosts. A recent study by scientists at the University of Aberdeen, Scotland, and the University of Tehran, Iran, found that tapeworms such as Anthobothrium, had concentrations of cadmium and lead, two heavy metals, that were as much as 455 times that of their hosts. The scientists suggest in their paper that parasites can serve as useful bioindicators - squishy little canaries in coal mines, if you will.

You can read about this in the original paper or on this site.

Image is of the type species of the genus Anthobothrium, A. cornucopia, from its original description in 1850.