Clistobothrium carcharodoni

The parasite for today is found in a celebrity of sorts, the star of the film Jaws and its sequels - the famous Great White Shark. Unlike its host - which is well-known for being big in every sense - Clistobothrium carcharodoni is a tiny little worm measuring no more than a few millimeters in length. However, what they lack in size, they make up for in numbers, as over 2000 of them can be found in a single shark.

Tapeworms in general have complex life-cycles with many different hosts, and C. carcharodoni is no different. The life cycle of tapeworms which live in marine animals such as the great white shark are difficult to unravel. That is because the larvae lack many of the diagnostic characteristics which are used to identify the adult worms, so it is next to impossible to match the identity of the larvae with adults based on their morphologies. But with the advent of molecular techniques such mystery are becoming more commonly solved.

One of my former colleagues from Otago University - Haseeb Randhawa - was able to use key genetic markers to confirm that adult C. carcharodoni found in the gut of great white sharks were identical to tapeworm larvae which have previously been found in dolphins. These larval tapeworms congregate in the tail, back, belly and groin region of the dolphins - all parts preferred by the great white sharks as the finest cuts of meat from Flipper. His study confirmed the role of dolphins in completing the life-cycle of C. carcharodoni.

So while Flipper and Jaws are famous superstars which grab all the public attention, to a tapeworm like C. carcharodoni, all those aquatic celebrities simply serve as way stations in the cycle of life.

Reference:
Randhawa, H. (2011) Insights using a molecular approach into the life cycle of a tapeworm infecting great white sharks. Journal of Parasitology 97: 275-280.

Chondracanthus parvus

Chondracanthus parvus is a parasitic copepod that parasitises the smooth-cheek sculpin, Eurymen hyrinus, by attaching itself to the inner side of the fish's operculum (the flap covering the fish's gills). Chondracanthus parvus belongs to a family of parasitic copepods known as the chondracanthids, which contains 160 species, all of which are parasites of marine fishes. Phylogenetic studies of the chondracanthids indicate that these copepod have consistently co-evolved with their hosts, and their phylogeny closely reflects the evolutionary history of the fish that they infect. Such parasites are like heirlooms of the evolutionary past and phylogenetic studies conducted on these living markers can in turn shed light on the evolutionary history of their hosts.

Picture from Ho et al. (2006).

References:

Paterson, A.M. and Poulin, R. (1999) Have chondracanthid copepods co-speciated with their teleost hosts? Systematic Parasitology 44:79-85.

Ho, J-s., Kim, I-H., and Nagasawa, K. (2006) Copepod parasites of the fatheads (Pisces, Psychrolutidae) and their implication on the phylogenetic relationships of Psychrolutid genera. Zoological Science 22:411-425.

Herpyllobius vanhoeffeni

Regular readers of this blog will no doubt be familiar with the wonderfully weird and twisted morphology of parasitic copepods. However, this is probably the weirdest we have featured yet. Herpyllobius vanhoeffeni is a spooky-looking parasitic copepod which has all the trappings you might associate with an Lovercraftian horror tale. They are found in the Antarctic Penninsula, in waters 666-673m deep, and they parasitise a polychaete worm, Eulagisca corrientis.

The top picture shows a pair of females attached to the ventral surface of their host; note that the lower individual has a pair of lobe-shaped egg sacs extending from its side like wings. The bottom picture shows a specimen that has been dissected from the host, showing the rest of the copepod, which is usually embedded in the host. Overall, the whole parasite looks not unlike a bulbous skull resting atop a twisted stalk of a body.

Reference:
López-González, P.J. and Bresciani, J. (2001) New Antarctic records of Herpyllobius Steenstrup and Lütken, 1861 (parasitic Copepoda) from the EASIZ-III cruise, with description of two new species. Scientia Marina 65:357-366

Columbicola extinctus

Speaking of co-extinctions, here's a contribution that I just got from Anya Gonchar. Columbicola extinctus is a louse that was specific to the Passenger Pigeon, the bird that forever disappeared in the early 20th century. In addition to many advantages of the narrow specialization, C. extinctus has experienced the most drastic of its drawbacks: it has followed its only host into extinction. This could have been one of the impressive examples for a discussion regarding specialist vs. generalist strategies in parasites, if the story hadn't suddenly taken a happy turn. C. extinctus was rediscovered from the Band-tailed Pigeon, while its fellow pseudo-extinct louse C. defectus was suggested to belong to a different species Campanulotes flavus that is still safe and sound. Still, parasite coextinction is documented in numerous other cases where we may not count on such good luck. Fortunately, there is now a large body of literature featuring related topics so that the problem is not neglected. The origin of this blog goes back to celebrating the year 2010 as an International Biodiversity Year. As the previous entries have shown, parasite diversity is enormous indeed. Yet, some parasite species’ existence is challenged. Further reading: Koh L. P. et al. 2004. Species coextinctions and the biodiversity crisis. Science 305, 1632. Dunn R. R. et al. 2009. The sixth mass coextinction: are most endangered species parasites and mutualists? Proc. R. Soc. B, 276, 3037-3045. Clayton D.H., Johnson K.P. 2003. Linking coevolutionary history to ecological process: doves and lice. Evolution, 57(10), 2335–2341. Johnson K.P. et al. 2003. When do parasites fail to speciate in response to host speciation? Syst. Biol. 52(1), 37–47. Johnson K.P. et al. 2009. Competition promotes the evolution of host eneralists in obligate parasites. Proc. R. Soc. B, 276, 3921–3926. Image is of Campanulotes flavus, from the paper: Price et al. 2000. Pigeon lice down under: taxonomy of Australian Campanulotes (Phthiraptera:Philopteridae), with a description of C. durdeni n. sp. Journal of Parasitology 86:948-950.

Ixodes neuquenensis

Today's parasite is a tick described from an endangered marsupial. Ixodes neuquenensis is an ectoparasite of a unique little marsupial known as monito del monte or "mountain monkey" (Dromiciops gliroides).

The "mountain monkey" is the only species still alive from an ancient lineage dating back more than 40 million years. Due to habitat loss, the population of this little marsupial has declined over recent years. This is bad news for I. neuquenensis because it is a very host-specific tick. If the "mountain monkey" goes extinct, it will also spell doom for this tick, along with a whole suite of other parasites and symbionts which are dependent upon this little marsupial.

Reference:
Guglielmone AA, Venzal JM, Amico G, Mangold AJ, Keirans JE (2004) Description of the nymph and larva and redescriptions of the female of Ixodes neuquenensis Ringuelet, 1947 (Acari: Ixodidae), a parasite of the endangered Neotropical marsupial Dromiciops gliroides Thomas (Microbiotheria: Microbiotheriidae). Systematic Parasitology 57:211–219

Philophthalmus gralli - update on the "Parasite of 2010"

Last year the most “yuck” votes were cast for a photo of Philophthalmus gralli in the eyes of a rhea at the Phoenix Zoo. Melanie Church, the vet who treated the rheas, gave me a back-door tour of the zoo in January. The three rheas are doing fine. She removed most of the flukes manually, treated the eyes with an anthelmintic ointment, and the birds are now virtually parasite-free. The rheas have been moved to a pen where the snail intermediate hosts are not present to prevent re-infection.

Contributed by Mike Kinsella.

Rugogaster hydrolagi

Today's parasite is a strange worm found in a habitat that may shock and bewilder many readers on multiple levels. It's a worm that lives in the rectal gland of the spotted ratfish (Hydrolagus colliei). The spotted ratfish belongs to an enigmatic group known as the chimaera, an ancient group of cartilaginous fish that branched off from sharks almost 400 million years ago. The parasite itself is just as mysterious - it belongs to a group call Aspidogastrea (we have featured other species from this group on the blog before - Lobatostoma manteri and Aspidogaster conchicola), which made the evolutionary split with the far more diverse digenean trematodes probably also a few hundred million years ago (unfortunately, most parasites don't leave fossils). Rugogaster hydrolagi can grow up to 15 mm long (a bit over half an inch), and is so-called due its "rugae", which are the ridges on its body that give it a corrugated, accordion-like appearance. The life-cycle (like most aspecst of its ecology) is unknown, though like other aspidogastreans, it most likely features a mollusc intermediate host.

Photograph by Klaus Rohde

Pygidiopsis macrostomum

Pygidiopsis macrostomum is a freshwater digenean from Brazil. Like most otherdigenean trematodes, it has a three-host life-cycle. It asexually multiplies in its first intermediate host, the snail Heleobia australis, producing cercariae (pictured) which are released into the surrounding water. The cercaria swims in an series of small, stepped leaps, and then spins rapidly on its own axis once it sinks to the substrate, almost like a tiny aquatic ballerina.

All this dance-like motion attracts the attention of guppies, the parasite's second intermediate hosts, which ingest the parasite and become infected. The parasites burrow into the mesentery tissue of the fish, where they form a cyst and await ingestion by the definitive host where the worm will mature into its adult stage. While the adult specimen of P. macrostomum were first described from a rat, a subsequent study have also found it in the piscivorous bat Noctilio leporinus which, given its diet, is more likely to be the parasite's usual definitive host.

Reference:
Simões et al. (2009) The life history of Pygidiopsis macrostomum Travassos, 1928 (Digenea: Heterophyidae). Mem Inst Oswaldo Cruz 104:106-111.

Contributed by Tommy Leung.

Opechona sp.

Today's parasite hails from the San José Gulf of Argentina. Opechona sp. is a digenean trematode which uses the intertidal snail Buccinanops cochlidium as a first intermediate host. The parasite sets up shop within the snail's gonads where it starts cloning itself, eventually castrating the snail through physical destruction of the gonad tissue. These clonal stages (known as rediae) produce free-living larvae called cercariae (pictured) that are released from the snail into the surrounding water, where they infect the next host in the life-cycle. This parasite reaches its peak prevalence during summer when water temperature is at its highest. While the life-cycle of Opechona is not fully known, related species have been recorded to infect jellyfishes as the second intermediate host in their life-cycle, and the period of highest cercariae emission for Opechona during summer may possibly coincide with the high abundance of jellyfishes during that season.

References:
Averbuj, A. and Cremonte, F. (2010) Parasitic castration of Buccinanops cochlidium (Gastropoda: Nassariidae) caused by a lepocreadiid digenean in San José Gulf, Argentina. Journal of Helminthology 84: 381–389.

Contributed by Tommy Leung.

Colobomatus sillaginis

Colobomatus sillaginis is a parasitic copepod that lives in the head of two species of fish (commonly known in Australia as "whiting") in the genus Sillago (Sillago maculata and Sillago analis). This copepod dwells in the system of cephalic canals in the head of the fish. Interestingly, while the gut tracts of males and juvenile females are bright green, the gut of mature female copepods are usually coloured red or black. Living in the cephalic canal alongside C. sillaginis are small ciliates that are bright green due to the symbiotic algae living within them. These ciliates can be so numerous that some fish have a greenish tinge around front of the head. The male and juvenile female copepods graze upon this turf of abundant food. However, once they become mature, the female takes to feeding on blood, probably due to the physiological demand of egg production, rather like a female mosquito which normally feeds on nectar, but needs to obtain a blood meal for egg development.

Reference:
West, G.A. (1983) A new philichthyid copepod parasitic in whiting (Sillago spp.) from Australian waters. Journal of Crustacean Biology 3: 622-628.

Contributed by Tommy Leung.