Friday Harbor Marine Laboratories, University of Washington
San Juan Island, Washington
Archival Pigment Print
Curling its body and bristling the appendages (cerata) on its back, this nudibranch strikes a defensive pose. At the tip of each appendage is a brown sac filled with stinging cells. When disturbed, the animal discharges the cells via tiny pores. Remarkably, the stinging cells are not produced by the nudibranch itself: It appropriates them from its prey, tiny colonial animals called hydroids, which are related to sea anemones and jellyfish. After a meal, the stinging cells are transferred from the stomach to the sacs at the ceratal tips via red-colored fingers of the digestive system, plainly visible in the photograph. The cells are stored in the sacs for the nudibranch’s own defense.