Thursday, April 14, 2016

Terrestrial Flatworm in Minnesota

I've come across these flatworms from time to time at Westwood Hills Nature Center. I was never really sure of what type of animals they were. I think the thought process probably went something like this:
"Hmmm, they look a bit earthworm-like but without segments. Maybe a little more leechish (not a word, but it should be), but there aren't land leeches in Minnesota, are there? A skinny slug? A really squishy, slimy insect larva of some sort."
At least that was the thought process, more or less when I came across a few of them last week under some logs while exploring at the nature center. But this time I managed to bring a few back and keep them alive and contained for a few days (they're good at escaping and/ or drying out and dying I've found) until I had a little time for some research. I discovered they were terrestrial flatworms of the genus Bipalium. I was surprised at the amount of information available and the bizarreness of these flatworms. I couldn't decide where to take this post and what to write, there were so many directions to go in. The creative impasse ended when I decided to make series of pictures to convey some key facts and points of interest; a Bilpalium info graphic.
Most flatworms are aquatic. These aren't, but they still need a moist habitat. They are originally from SE Asia, and have likely spread in soil and on plants from commercial greenhouse. There are probably five species of Bipalium flatworms scattered throughoutin North America. B. adventitium is likely the species I found.
I'm always interested in where a new (to me) organism fits into the general taxonomic scheme.
Each box represents a phylum. The bigger ones on top are the phyla that I have some combination of first hand observation, knowledge of, or that have representatives in MN (the Feinberg Index of Familiarity perhaps). I have freely mixed common and scientific names.
Anatomically, flatworms are a very simple group of animals.
a. eyespots for sensing light and dark
b. ganglia or "brain"
c. gastrovascular cavity where digestion and circulation take place
d. mouth/ anus with evertable pharynx
There are more body parts: muscles and cilia for movement, something called a flame organ to control water content, and since they are hermaphroditic, male and female reproductive organs. But the take home message is a simple body plan.
And last, it has been discovered that some species of Bipalium flatworms contain the neurotoxin Tetrodotoxin including B. adventitium. This toxin is found in a wide variety animals, and may be the byproduct of bacteria living inside the animal; the host animal is immune to the toxin's effects and utilizes it for defense or predation.