6 Replies to “U is for Urchins”

  1. Yes, they are attractive to look at, and it’s fascinating to observe at close quarters the way their spines are arranged in a pentamerous fashion, each one attached and articulating on a small tubercle.

  2. Yes, the shape of the test varies quite a bit between the species even though they are all built to the same basic design with a five way pentamerous symmetry, just like other members of the Ecinodermata like starfish and sea cucumbers.

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