Aug 29, 2009

Primitive Planarian

Photo source: Georgia University FACES
Should you stumble across one of these creatures, which are rare in most parts of the US, you have one of three options. 1) Resign yourself to the fact that you're the sorry sap at the beginning of an alien invasion that has the misfortune of having made first contact, and you'll be consumed and rendered a zombie, or 2) simply shrug, smash it, and move along, or 3) do a bit of investigation and find out what it is.

If you choose that last option, you'll discover that you have indeed encountered an invasive species (unless you're in east Asia), one that has made its way around the world in nursery pots (or in human spinal columns...). You've encountered a Land Planarian (which happens to be a great name for an alien race).

These primitive flatworms have no circulatory or respiratory system, and no skeletal structure. They don't have eyes, and their mouth, which is halfway down their belly, also double as their anus (which I've found to be true among quite a few humans, too). They ambulate by gliding upon a bed of mucus of their own making, and they dine on earthworms, slugs, and human happiness. They're harmless, unless you are a happy human, or an earthworm (the planarian will attack prey 10-times its size to suck out worm juice).

Last but not least, they can procreate by laying eggs, or by budding, or by simply squeezing off part of its tail, which will then sprout into a new planarian.

Thanks for the planarian, David.

20 comments:

jenjen said...

These dudes are all over our college campus. Hardly ever see an earthworm anymore. Not sure if they do the same work in the soil as earthworms.

Bambi Slayer said...

Not too sure about thembeing introduced. I grew up seeing these flat worms that can get rather long about 1 foot, in La. I remember seeing these about 45 yrs ago. You can split the head and it will turn into siamese 2 head worm wanting to go in seperate directions.

bonni said...

I have some vague recollection that if you cut them in half (lengthwise, I'm thinking), they can regenerate and become two worms.

And I definitely recall something about cutting them in half lengthwise only along the top part, through their, for lack of a better term, head, whereupon they will proceed to grow two heads.

Or maybe I'm dreaming. Back in my day, we used to dream of cutting worms in half. It was what we did for fun on a Saturday night, and we were grateful!

Oh, I also had a very, very minor and nitpicky nitpick about the use of "latter" when there were actually three options, but I think I won't include it. It'll make me look like a grammar nerd. Which I am, but I don't want to look like one.

Raging Wombat said...

I fixed it, just for you, bonni.

Anonymous said...

Latter means "more recent" (not "second"). Its use to reference the last item of a list of more than two is perfectly acceptable.

Tracy from Oz said...

Gross.

Betsy Hammer said...

Wombat, sometimes I want to beg you--BEG YOU--to please delete certain posts because they are so unbelievabley ugly. I'll be squinting every time I visit for the next week just to be sure I don't accidentally spot it again.

Raging Wombat said...

I'll do what I can Betsy. But no promises...

Erin said...

I have aquatic planaria--about 150 of them--as pets. The species I have (Dugesia dorotocephala) gets to be only an inch long at most. They are roughly arrow shaped, and unlike land planaria, they have two unmistakable eyespots in their heads that give them an adorable cross-eyed appearance. They reproduce asexually on a regular basis by separating their upper bodies from their tails--the former regrows its tail and the latter regrows a pharynx and head. I have read that planaria can be cut into as many as eight pieces and still regenerate a whole planarian from each piece.
Let it be known that planaria, unlike the parasitic members (flukes and tapeworms) of their phylum Platyhelminthes, are utterly incapable of parasitizing or harming humans. I would love to encounter a land planarian some day. I would also love to keep one as a pet, but I've found that, at least among aquatic planaria, most species are not nearly as hardy in captivity as Dugesia dorotocephala.

Anon three of Nine said...

Erin, what kind of setup do you have to keep the planaria? I have tried two times to keep an unknown Dugesia sp. in jars, but I haven't been able to keep them alive for more than a couple of weeks. They really liked boiled egg yolk, but for some reason they would all slowly die.

also, where did you get that particular species? The ones I tried to keep were from a pond.

I used to see terrestrial planaria when I would walk to the bus stop when I was in high school, but I haven't seen one since then. I forgot why I couldn't keep them in captivity... I think they just wouldn't eat.

Erin said...

I'm glad to hear from a fellow planarian fan! To answer your question, about half of my planaria were adopted from a biology lab, and the other half started out as ten individuals I collected under rocks in a shallow stream--they reproduced asexually to reach their current abundance. Both are D. dorotocephala, with the triangular heads and jutting triangular auricles, but the lab specimens are a genetically distinct population: they are slightly smaller and have darker pigmentation.

I've had my planaria for about a year and a half so far, and my setup is simple. I keep the planaria in a clear plastic jar with a lid (I screw on the lid because it seems to prevent water from evaporating and leaving a calcified crust on the sides). I originally had them in small Carolina Biological Supply jars, but I recently upgraded to a peanut butter jar.

I feed them once a week. Their food, which is frozen, ranges from hardboiled egg yolk to chopped up earthworms (I collect dead worms after it rains) and sections of captive-raised tobacco hornworms that had been killed for a science project (which, for the record, was not my idea). I'm not sure exactly what volume of food they need, so I guess. I have read that fifty planaria require a pea-sized portion of egg yolk, but if they were fed beef liver, the portion would be bottlecap-sized. After a few hours, I always remove the food and change the water.

I change their water once per day, and I use untreated well water, lake water, or water from the stream where the wild population was collected. I would never use chlorinated or distilled water. Also, a few times a week I remove scum and detritus from the bottom and sides of the container by dislodging it with my finger, taking care to gently push planaria out of the way.

I have kept several species using these methods, but for some reason, all the species other than D. dorotocephala and an unidentified black species did not eat any of the food I offered and shrunk until they died or until I released them. If your planaria have been raised with similar methods yet fail to thrive, it might be that they have different dietary needs.

K I ran out of 3s said...

you change their water once per day? Hmmm... I may have killed my planaria because I didn't change it often enough. Apparently I also fed them WAY too much.

Thanks for the info! I'll try it out next time I get my hands on some planaria.

How were you able to ID your wild-caught ones? I just searched "Dugesia identification" and other things, but I couldn't find anyhing.

On a totally random note, here's a really neat land planarian: http://www.flickr.com/photos/budak/1148748518/

Erin said...

Wow, that land planarian is beautiful! Its black and white bands remind me of a sea snake (more specifically, a sea krait).

Planaria, unfortunately, are so obscure that detailed information about them is scarce and difficult to find. The closest thing I have found to a comprehensive planarian taxonomic key is this staggering online database of planaria species. http://devbio.umesci.maine.edu/styler/turbellaria/turb2.php?action=1&code=7027 That link goes to the genus Dugesia, but there are tons of other non-Dugesia species that are also listed on the site. In fact there are so many taxonomic branches that browsing it is rather overwhelming. Most of the more common species have an annotated illustration (When browsing the species in a genus, look for a filmstrip icon in the table next to a species name). However, many of the listed species don't have any images or notes to enable identification.

I am confident that my planaria are Dugesia dorotocephala because I have looked at most every available picture in most every genus, and no other species has both a triangular head and long, sharp auricles. They also match what photos I can find of the species.

I'm glad I could help, and I wish you luck with your future planarian-raising endeavors!

ThreeBites said...

And so, the internet fails us again. I used to be amazed at how much information there was in the internet, but now I tend to be amazed at how little there is. Given all that the human species knows as a whole, the amount of information in the internet is pathetically small.

Anyway, rant over. Thanks!

bonni said...

Wow, Anonymous #1, you're an even bigger nerd than I am. I went and looked it up and I see that I stand corrected. You, Anonymous (why post anonymously?) are a much bigger nerd than I am. I am humbled by your nerdness. And somewhat puzzled by your anonymity.

I hereby apologise for the very minor, nitpicky nitpick which I didn't want to mention because, as it turns out, I was wrong.

Learn something new every day, eh? :)

Anonymous Nerd said...

My reason for anonymity is well explained in the words of a fellow nerd: my post would "make me look like a grammar nerd. Which I am, but I don't want to look like one."

Zookeeper Gabe said...

These things are amazing, I got to watch them hunt while in Honduras.

Anonymous said...

Anonymous 3 is actually David Hasselhoff.

Anonymous said...

Writing from UT-Austin, after heavy rains last night there were several of these planarians on the sidewalk. I didn't know they were "rare."

Matt said...

I came across this beautiful specimen - http://www.flickr.com/photos/maixiu/4938336688/ - not far from my home in Singapore. And across your website when I was researching it. Although I didn't collect it, the information here is very useful!