Eustrongylides ignotus

Eustrongylides ignotus is an extremely pathogenic nematode which lives in the wall of the stomach (proventriculus) of herons and egrets and has caused die-offs in nesting colonies of some birds. Its bright color has earned it the nickname of “the big red worm.” The life cycle involves oligochaetes as the first intermediate host and various fish as the infective intermediate host. If the small fish are ingested by larger fish, reptiles, or amphibians, these can act as transport hosts. The color in this larval worm in a mosquitofish has been bleached out by the preservative. If straightened out, it would be longer than the fish.

Contributed by Mike Kinsella.

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.