This sea urchin with big sacs is called Phormosoma. A publication suggested that the sacks serve as hypodermic needles for self defense.
Sea Urchin
Image courtesy of the NOAA Office of Ocean Exploration and Research, Exploring Deep-sea Habitats off Puerto Rico and the U.S. Virgin Islands. Download larger version (jpg, 1.4 MB).
This sea urchin with big sacs is called Phormosoma. A publication suggested that the sacks serve as hypodermic needles for self defense.
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