Here's another companion for the previously posted cockle shells and harp snail shells: a sea urchin in royal icing. All you need is a pastry bag filled with medium consistency royal icing (the icing I had on hand was relatively thin; I'm definitely going to re-do these urchins when I make another batch), a dusting pouch filled with a 50/50 mix of powdered sugar and cornstarch, round tips #12 and #2, a parchment paper square for each urchin, round tooth picks, a flower nail (optional; I like using flower nails for almost everything), a glue stick, and Wilton Pearl Dust (if you'd like your urchins to be shimmery; and who wouldn't?!). Start by sticking a parchment square to the flower nail with a dab from the glue stick.
Hold the #12 tip just above and parallel to the surface, and squeeze out a ball about half an inch across. Stop pressure, pull the tip straight up and away, and if a peak forms, tap it down with a fingertip you've touched to the dusting pouch.
Tap a toothpick against the dusting pouch, then lie it against the ball several equally-spaced times, radiating outward from the center.
In the center, use the tip of the toothpick to make a hole. If you really want to know what that hole is, go here. Bon appetit!