Chitons & Urchin by marlin harms
Via Flickr:
Another one from the archives. Chitons: left–Tonicella lineata, Lined Chiton or Tonicella lokii, Loki’s Chiton; right–Mopalia lignosa, Wood Chiton or Woody Chiton. Urchin: Strongylocentrotus sp. The chitons were probably near 2" (5cm) long. Montana de Oro State Park, San Luis Obispo Co., CA

Purple sea urchin (Strongylocentrotus purpuratus)

The purple sea urchin lives along the eastern edge of the Pacific Ocean extending from Ensenada, Mexico to British Columbia, Canada. This sea urchin species is deep purple in color and lives in lower intertidal and nearshore subtidal communities. It normally grows to a diameter of about 4 inches and may live as long as 70 years.

photo credits: Taollan82, Wilson44691, Purpuratus, flickr