Sea Urchins belong to Class Echinoidea (Phylum Echinodermata).
Unknown Sea Urchin 1
This is easily the most common sea urchin found on Axial. It is often observed hiding among the lobed basalt lavas. Its size is only 10-15 cm in diameter.
Spiny Sea Urchin (Tromikosoma panamense)
The Tromikosoma panamense sea urchin has only been observed on a few occasions, and is not common at Axial. This specimen was seen at the base of Axial Seamount. The T. panamense has a hard armored shell, consisting of small plates covered in spines.