At least in this drawing by “Weird Bug Lady” they do.
And good thing! It seems that WBL is a talented artist because planarian worms do in fact look like penises in real life. I wouldn’t recommend trying to use her stuffed planarian toys as dildos, though, as they are likely too squishy to fit in tight orifices (recall the DIY airplane peanut dildo incident, if you will).
Check out more of Weird Bug Lady’s very cool art in her Etsy store.
[via Weird Bug Lady]