The importance of mucus produced by jellyfish species remains as understudied as their feeding behavior. Here, we study medusae under captivity, ascertain the role of mucus, and describe its feeding behavior. Between February and March 2019, live adult cannonball jellyfish, Stomolophus sp. 2, were collected in Las Guásimas Bay (Gulf of California, Mexico) and were offered fish eggs, mollusk “D” larvae, or Artemia nauplii in 4-day trials. Descriptions of feeding structures were provided for S. sp. 2. Digitata adhere food and scapulets fragment them, which, driven by water flow, pass via transport channels to the esophagus and the gastrovascular chamber where food is digested. Due to stress by handling, medusae produced mucus and water, lost feeding structures, and decreased in size. Based on our observations and a thorough literature review, we conclude that the production of mucus in S. sp. 2 plays several roles, facilitating capture and packing of prey, acting as a defense mechanism, and facilitating sexual reproduction; the latter improves the likelihood of a population persisting in the long run, because fertilized oocytes in mucus transform to planulae, settle, and transform into asexually reproducing polyps. Polyps live longer than the other life stages and are more resistant to adverse environmental conditions than the medusoid sexual stage.

Exploitation of the cannonball jellyfish (Stomolophus sp. 2) is increasing in Mexico and USA due to successful fisheries associated with seasonal blooms in coastal areas. Previously, it was proposed that such blooms could be identified by recognizing the presence of young stages in the water. In our work, we aim to describe the young stages (ephyra and metaephyra) found in the Las Guásimas lagoon, Sonora, Mexico. The description of specimens is based on photographs, drawings, and morphological measurements aimed at helping in the early detection of blooming events.