By Mark Carnall, on 16 April 2012
No they’re flatworms. Boom boom. Apologies for the awful pun but worm based-jokes are thin on the ground unlike earthworms which are thin and in the ground. Oh dear. This post is a continuation of the occasional series highlighting objects from the stores and recently I’ve turned my attention to Flatworms.
Worms are an amazing ‘group’ of animals although once again common names clash with scientific classification as there’s more than one way of being a ‘worm’. In fact there are ‘worms’ that are more distantly related to each other than we are to fish, amphibians, birds and reptiles. For example, ribbon worms and arrow worms are more different than all animals with a backbone are from each other. It turns out that having a wormy body plan is a relatively successful way of being an organism but confusingly humans have the habit of calling any organism that is thin and long a worm. Further adding to the confusion is that there are a lot of animals which aren’t thin and long but are still worms. I won’t go into the minutiae of worm taxonomy, handily there’s this very useful wikipedia page about it for those of you keen on knowing your worms from your worms.
Most recently I’ve been working through the flatworms AKA Platyhelminthes. It is a very diverse group of organisms that occupy virtually every niche from free living predatory terrestrial and marine species through to the parasitic flukes and tapeworms that are more familiar to most people. Just over half of all known flatworm species are parasitic and as with all parasitic species have phenomenal, if somewhat morbid, existence. There’s not enough room here to cite every amazing example but parasitic flatworms undergo a dizzying array of techniques and often have to move from three or more completely different host species as they mature from eggs through to adults. Take for example, the giant intestinal fluke, Fasciolopsis buski which starts off as a free-living organism in water and then invades the body of one of a limited number of snail species and then becomes free living again to find a water plant where it then turns into a cyst until it is eaten by a mammal where it develops into a 5-8cm long fluke, lays its eggs which hatch in water. Such a risky life cycle surely sees the untimely death of millions of F.buski a year; if they fail to find a host snail, plant or mammal or if the eggs don’t make it to a water source. Their counter strategy to this risky business is that adults, safely attached inside the intestinal wall of a human or pig produce up to 25,000 eggs a day for a year in order to guarantee that some eggs survive.
The relatively small collection of platyhelminthes at the Grant Museum represents some of the range of flatworms both in terms of the different stages in the life cycles and also the surprising diversity of host species. A quick survey reveals that we’ve got examples of flatworms from python, dog, rabbit, mongoose, lemur, sheep, shark, horseshoe crab, cat, horse, mouse, salmon, great northern loon (a bird), bramble shark, cow and halibut. One specimen in particular (pictured in the centre above) raises some interesting historical and ethical questions as it is a specimen of the beef tapeworm, Teania saginata (labeled under the old name Taeniarhynchus, I know, I know I’ll get around to it) that had been taken from veal deliberately infected with the tapeworm. A further point of historical interest is that it was transferred to the Grant from the Royal College of Surgeons.
I doubt we’d know half as much about flatworms if it wasn’t for their detrimental effects on human and domesticated animal health. Flatworms can cause a wide range of problems in animals from a relatively increased appetite from gut parasites through to bilharzia, and even epilepsy from species that infect the central nervous system. Deliberately infecting livestock with parasites may seem cruel and morally objectionable to our modern sensibilities but back in the 1890s such research methods were key to understanding how best to prevent infection of humans and the animals we like to eat and keep as companions.
Well I’d love to go on and on about flatworms as part of my secret mission to lift the lid on animals which aren’t Hollywood enough but that’s perhaps best left for a future installment of dun dun dun IT CAME FROM THE STORES!