I’ve posted about planaria once before: after I collected a number of Polycelis coronate from a local stream (A wiggly quest: hunting (and photographing) the wild flatworm!). I noted at the time that Polycelis looks quite different from the planaria most people know from textbooks and high school biology classes. I also suggested that I would probably post photos of another species (or two) of planaria at some point. Well, here they are…
The pictures I have posted today—with their arrowhead shaped heads and crossed eyes (eyespots really)—are more “classic” looking planarians. I’m not exactly sure what species they are. I originally assumed they were brown planaria (Dugesia tigrina), which are very common. However, these specimens have a more rounded head than brown planaria I have seen before; and there is a light oblique dash on the upper side of each auricle (see the photo below). These characteristics suggest that these are specimens of Cura foremanii. However, I’m not experienced with Cura, and the oblique markings are pretty faint, so I am not completely sure.
Part of the reason I can’t be sure of the identification is that I didn’t collect them in the wild. When I was at the pet shop last weekend buying the praying mantis I have been writing about (in my last two blogs) I saw that one of their aquariums was infested with these critters. Aquarium hobbyists consider them to be vermin, but I was thrilled to see them and of course asked if they could collect me some. A long discussion ensued between the staff as they tried to figure out how to do so (I explained that they just needed to scrape them on the glass with a net). Anyhow, after about 15 minutes they were finally able to bag two specimens for me to take home. I’m sure I qualified as one of their “odd” customers that day…
Photographing these little beasts couldn’t have been much easier. I just put them in a white tray holding a very shallow amount of water and shot them with the 35mm macro lens and ring flash, shooting straight down to avoid any reflections of the flash on the surface of the water.
After taking a series of photos of the worms gliding around the tray I dropped in some very tiny fragments of frozen bloodworms (midge larva, family Chironomidae). When the planaria came close to the fragments of bloodworms they started to search and began feeding as soon as they found the bloodworm bits.
The mouth of a planarian is in the middle of the ventral surface of the animal, and not in the head. These worms feed through a tube-shaped pharynx that extends out of the mouth. You can see in the photos that the planaria feed by wrapping around the food item and positioning their ventrally positioned mouth against the food.
Next I need to photograph these same critters on a more natural background. I’d also like to capture some photos that clearly show the extended pharynx as they feed.
The technical stuff:
Camera: Olympus E-620 digital SLR
Lens: Zuiko 35mm macro
Settings: manual exposure (F14 @ 1/125 sec)
Lighting: Olympus RF-11 ring flash (1/8 power)