What are those animals that live in the fresh water rivers in Wa. state?

We used to fool with them as kids. They are about an inch long. They make a long skinny tubular shell from tiny rocks. Their shell looks like concrete. There is a little crab like thing that lives inside. What the heck is this creature. We always called them periwinkles, but my biologist friend thinks I'm insane. He's never heard of them. Please if anyone knows what these things are, do share.

What are those animals that live in the fresh water rivers in Wa. state?
Typically, a periwinkle more commonly referrs to a molusc that has a "snail-like" shell. However, in some regions periwinkle referrs to the larvae of a caddisfly. I think this is what you're describing.





The subaquatic larva of a caddisfly use thier own glue to bind sand, gravel and other objects on the riverbed to make thier case. Depending on the environment, this case varies in looks.





Since you've seen them and know what the creature you're looking for looks like, here's some pictures of caddisfly larvae and you can tell if it is the mystery creature or not.





http://www.bugsurvey.nsw.gov.au/html/pop...


http://www.whatsthatbug.com/images/caddi...


http://www.deh.gov.au/water/rivers/nrhp/...





This should put your biologist friend at ease.
Reply:Fish !!!
Reply:We have the same thing in OR, and they are great for fishing. I've never heard them refered to as anything but periwinkles. They're fairly widespread, I was watching an animal planet show a while back and saw them on the show and they were in the Northeast states, New Hamshire I think, and they refered to them as periwinkles too. While I'm sure they have a scientific name I think you're biologist friend is either a city kid or insane themselves! (or possibly pulling your leg) I do know that they are a larvae of a type of waterbug, a fly of somesort I think, but don't remember which one right now.