Black sea nettles are carnivorous. Their mouth is located at the center of one end of the body, which opens to a gastrovascular cavity that is used for digestion. It has tentacles that surround the mouth to capture food. Nettles have no excretory or respiratory organs. They generally feed on zooplankton and other jellyfish.[4] Nettles immobilize and obtain their prey using their stinging tentacles.