If you cut the sea urchin along the equator you will see the following:

• Am and Im are the ambulacral and interambulacral areas respectively.
• A is the "top" and B is the bottom or mouth side.
• Gonads are usually yellow to orange in color [about the same color as the eggs]
• Stomach and Intestines are usually olive drab to brown in color.

From The Fishery Biology of Sea Urchins in the Family Strongylocentrotidae, Washington Department of Fisheries, 1976