Rhizostomeae

Rhizostomeae is an order of marine jellyfish within the class Scyphozoa, commonly referred to as true jellyfish. Members of this order are distinguished by the absence of tentacles on the bell margins; instead, they possess numerous oral arms that are fused into a complex, often branched, structure surrounding the mouth. This morphological adaptation allows efficient capture and transport of planktonic prey to the gastrovascular cavity.

The order comprises several families, the most diverse being Rhizostomatidae, Lobonematidae and Cepheidae. Species range from small, translucent forms a few centimeters in diameter to large pelagic medusae exceeding one meter in bell width, such as the well‑known barrel jelly (Rhizostoma pulmo). Rhizostomeans are distributed globally, inhabiting temperate to tropical waters, with some species forming seasonal blooms in coastal upwelling zones.

Feeding ecology centers on filter‑feeding and passive prey capture. The oral arms bear numerous small, adhesive tentilla that trap zooplankton, fish larvae, and organic particles. Digestive processes occur within a highly branched gastrovascular system that distributes nutrients throughout the body. Many rhizostomeans exhibit seasonal life cycles, with a benthic polyp stage (scyphistoma) that produces medusae via strobilation.

Ecologically, rhizostomeans contribute to trophic dynamics by linking primary producers and higher predators, and their blooms can affect fisheries and tourism due to high biomass. Some species possess bioactive compounds of pharmaceutical interest, prompting research into their potential antimicrobial and anticancer properties. Conservation concerns are minimal, though climate‑driven changes in ocean temperature and acidity may alter distribution patterns and bloom frequency.