Heteroschisma canadensis is the last of the three blastoid species that I've found at Arkona. It's the smallest and is often referred to as "ice cream cones". As you can see they are about the size of rice grains so one has to be looking really close to find them. All four specimens that I found came by sifting through some eroded gravel.
Oral surface (top)
Basal surface (where the stem attached)
The other two species that I have from Arkona are Nucleocrinus elegans and Hyperoblastus reimanni. All three were found in the Hungry Hollow member of the Widder formation (Devonian, Givetian stage).