On a visit this past winter to a borrow pit that is working the Mahantango formation I came across a layer or lens of a delicate bryozoan. It's called Taeniopora exigua and generally it's found as small, broken pieces. At this location though there must have been a forest of these animals since they are preserved in such profusion and completeness.
Here is a large piece of mudstone which is riddled with the casts and molds of Taeniopora exigua
A couple of typical examples. Note that they are naturally flat shaped like a leaf and not round or stick like. The growth pattern is similar to another species called Sulcoretepora. The distinguishing feature between them is that Taeniopora has a central ridge that runs up the middle of most branches. You can see it in the specimen shown below.