Tetragramma sp. in Matrix-Texas

Description

Echinoids (sea urchins) first developed during the Paleozoic and continued to diversify throughout geologic history. These diverse animals are part of the phylum Echinodermata, which displays a 5-fold symmetry. Every echinoderm can be split into 5 equal segments.
When a sea urchin dies, the spines fall off because they're held on with soft tissue. The spines can be found articulated to the echinoid, but it isn't common.
This extremely complete specimen does have a couple of imperfections, as shown in the photos. Tetragramma is an irregular echinoid that is most commonly seen from Morocco and Texas.
Tetragramma sp., Cretaceous, Walnut fm., Bella County, Texas