Teenage Ninja Turtle Worms
Earlier this week, one of my colleague came across a long-necked turtle (http://en.wikipedia.org/wiki/Eastern_long-necked_turtle
) that had died at one of his field sites. I decided to make the most of the turtle's death by investigating what kind of parasites it might have harboured. After I opened up the body cavity, I found myself staring at a leaf-shaped, mango-coloured worm - it was Gigantolina elongata
- and I found 3 of such worms living in the turtle's body cavity, sliding sluggishly between its organs, each measuring about 3-4 centimetres in lengthGigantolina elongata
is a species of parasitic flatworm in a group call Amphilinidea
). There are only 8 known species of amphilinids (see this post http://krohde.wordpress.com/article/the-amphilinidea-a-small-group-of-xk923bc3gp4-21/
) and they belong to a larger group of peculiar "no-quite-tapeworms" call the Cestodaria
The Cestodaria is a sister group to Eucestoda
- also known as the "True Tapeworms"
. There are over 5000 known species of true tapeworms; they range in size from just a few milimetres long to some that grows to over 30 metres in length. Tapeworms are found in every vertebrates animals from fish to mammals and birds to reptiles and amphibians, and have been recorded from hosts in just about any environments from tropical forests to alpine lakes, from baking deserts to the arctic oceans.
In contrast to the far more successful Eucestoda, the Cestodaria is a limited to handful of species from an idiosyncratic collection of hosts including the fore-mentioned long necked turtles, as well as sturgeons, and ratfish. While of no economic importance, it is of great interest to evolutionary biologists who study the evolution of flatworms because even though it is related to the true tapeworms, it lacks many of the key characteristics of that group such as the scolex (the attachment organ at the "head" of the tapeworm which is armed with suckers and hooks) and proglottids (the egg-carrying segments that can be shed from the back of the tapeworm).Gigantolina elongata
has a complex life-cycle whereby the eggs produced by the worm leave the host turtle and hatch into larvae that embed themselves into the abdomen of freshwater crayfish, where they undergo the next stage of development. The worm reaches maturity when the infected crayfish is eaten by a long-necked turtle. When swallowed by the turtle, the juvenile worm penetrates the wall of the reptile's throat and move into the body cavity. There is a major problem with living as a parasite in that part of the host's body - the body cavity has no direct opening to the external environment. With the true tapeworms and other intestinal worms, dispersal of offspring is simply a matter of laying eggs and letting the host's usual digestive process do the rest. But the body cavity has no such opening so at this point, it is still a mystery as to how G. elongata
is able to transport its eggs to the outside world.
There is still much which is unknown about these peculiar worms, and evolutionarily speaking, it seems to be hanging out on a gnarled and lonely twig. Perhaps much like the tuatara and coelacanth, G. elongata
and its kind are remnant species of a once far more diverse and widespread group, and what I saw that day in the body of a dead turtle is all that is left from a once prolific empire of flatworms.
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