Here is a neat crinoid stem that my cousin found while at Lake Cumberland, Kentucky. It is a Mississippian period crinoid stem with a smaller one attached to its side. You can see the hold fast with its root like appearance holding onto the larger stem. A smaller stem then makes its way up to produce another crinoid.
It appears that the larger stem was still alive when this happened or at least its bottom portion was still standing when the smaller crinoid attached and started to grow.
The bottom picture shows both crinoids on their side and taken from the opposite side from the first picture.