The name nudibranch means “naked gills.” Many types of nudibranchs have developed external gills to absorb oxygen from the water. These feathery, ribbon-like organs can be very beautiful, and make it easy for a diver to distinguish nudibranchs from other kinds of underwater slugs. External gills “crown” the nudibranch above, called Chromodoris elizabethina (presumably named after the queen). The external gills can be clearly seen in the left portion of the photo. Divers might spot this nudibranch munching on coral polyps.