Cavechat.org

This looks like a Blastoid to me. What do you think?

(If any of you don't know what a Blastoid is look here: http://en.wikipedia.org/wiki/Blastoid)


(Found in Signal Light Pit.)

Definately a blastoid. The grove you see is the ambulacrum. The grove is actually seperated down the middle, with two lancet plates through which the blastoid would feed. Brachioles (delicate armlike appendages) would extend from the ambulacrum to aid in feeding. These are very rarely preserved. Echionderms have penagonal symmetry, so there are 5 ambulacra. A stem extends downward from the base of the crown (ed: the correct term is theca - a saclike body made up of imbricate plates surrounding the soft parts of the main body, as Greg points out below), which would be into the wall. The stem is similar to a crinoid stem and is usually broken free from the crown.

Yep, it is a blastoid. A fellow researcher calls them "cockroaches of the Mississippian". The Mississippian Era took place ~350 million years ago and blastoids were extremely common at that time. I've seen cave walls covered in them and thecas (like the one shown) littering the ground near shale outcrops. Too bad they went extinct. I bet they tasted like chicken.

I couldn't remember the correct term for the body.
When I took invertibrate paleontology, we went on a field trip to collect blastoid thecas at a quarry near Gore, Ok in Mississippian Limestone. You could pick up hundreds without swinging a hammer. We would collect extra to distribute to grade school classes. It was traditional to stop at the Wildhorse BBQ on the way back. Every year, the professor would very slyly throw a handful of blastoids into the parking lot. He would bet the most gullable person on the trip lunch that there are so many blastoids in the area that he could find one in the parking lot. Many times, students took him up on the bet and bought him lunch. The point of this rambling story is that, as wvdirtboy said, there are tons on them in Miss. Ls. I don't know if I could eat one though, with the crunchy shell and all.