It's No Fluke

Among the many zoological collections housed within the Museum of Life Sciences at King’s College London are two cabinets of microscope slides that have become known as the “Dawes Collection”, this having been assembled by Professor Ben Dawes who was Professor of Zoology at King’s College London during the middle of the last Century. Dawes was a parasitologist (more specifically a helminthologist; someone interested in flatworms and roundworms), and the cabinets contain a diverse array of parasitic helminth worms, many of them of medical and veterinary importance.

During a recent survey of the Dawes Collection, among the many fascinating gut worms, liver flukes and blood flukes, there came to light a rare specimen, D901, which at first sight, even to a parasitologist, appeared to resemble a fluke. However, this was no fluke. Its name is Amphilina bipunctata and despite the superficial resemblance to a fluke it is, in fact, a tapeworm even though it clearly does not have the long, segmented body that we traditionally associate with tapeworms. 

The worm is about 40mm long and the label on the specimen records that it was obtained from a White or Green Sturgeon collected in Oregon, USA. The species was first described by Riser (1948) from material also originating from Oregon, USA. Riser described the species from worms that he found in the Hopkins Marine Station of Stanford University in a jar understandably mis-labelled “Trematoda”, (flukes), the label with the specimens having the following information, “Dodson, Oregon. From coelom of sturgeon. Aug 1923. Carl D. Duncan”. It is tempting to speculate that Riser may have provided the King’ s specimen, but presently we have no documented proof of this.

Amphilinids such as A.bipunctata are an ancient group of monozoic ‘unsegmented’ (as opposed to the more usual polyzoic/strobilate , or ‘segmented’) tapeworms most species of which exist as hermaphroditic reproductive adults in the body cavity (coelom) of Sturgeons (Acipenseridae). Sturgeons are an ancient group of fishes living mainly in marine and estuarine habitats and returning to freshwater to breed. The life cycle of the parasite is complex and involves the laying of eggs by the adult worm which exit the body cavity of the sturgeon via coelomic pores in the body wall of the fish. The eggs are ingested by small aquatic crustaceans which function as intermediate hosts, and the larval stages of the parasite that develop are then infective to sturgeon when the crustacean host is eaten.

It has been suggested that in the distant past the original adult of Amphilina may have been a strobilate (segmented) tapeworm that lived in the intestines of a fish-eating ‘dinosaur’, possibly an aquatic reptile such as a plesiosaur, or ichthyosaur. This host would have become infected by ingesting the stage found in the coelom of the sturgeon. With the extinction of the original dinosaur host it is claimed that the reproductive role of the adult would then have effectively been taken over by the larval stage in the body cavity of the sturgeon, thus demonstrating the phenomenon known in zoology as neoteny, whereby individuals attain sexual maturity while retaining characteristics of a larval form.

The taxonomy of species in the genus Amphilina is both complex and controversial. Amphilina bipunctata has been regarded as being the same as another species Amphilina japonica (Goto & Ishii,1936) by some authors, but this position has been challenged by others, and there is still further work to be done. Extensive searches of other parasitological museum collections seem to suggest that the Amphilina bipunctata specimen at King’s College London is the only one in Europe, and it is in all probability the only one in existence outside North America. It therefore stands as an example illustrating the international importance of the collections at the Museum of Life Sciences.

References

• Goto, S. and Ishii, N. (1936) On a new cestode species, Amphilina japonica. Japanese Journal of Experimental Medicine. 14, pp. 81-83.
• Riser, N.W. (1948) Amphilina bipunctata n. sp. A North American Cestodarian. Journal of Parasitology 34 (6), pp.479-485.