Rhizostomeans

Rhizostomeans are a group of marine cnidarians belonging to the order Rhizostomeae within the class Scyphozoa, commonly referred to as true jellyfish. The name derives from the Greek “rhiza” (root) and “stoma” (mouth), reflecting the distinctive fused oral arms that replace a central mouth in most members. This morphological adaptation creates a complex, often lobed oral disc used for filtering plankton and small particles from the water column.

The order comprises several families, the most prominent being Rhizostomatidae, Cepheidae, Mastigiidae, and Stomolophidae. Species such as *Rhopilema nomadica* (the nomad jellyfish), *Aurelia aurita* (moon jelly, occasionally placed in related groups), and *Cassiopea* spp. (upside‑down jellyfish) illustrate the diversity of form and habitat. Rhizostomeans inhabit tropical, subtropical, and temperate seas worldwide, ranging from coastal lagoons to open ocean environments. Some species form large seasonal blooms that can impact fisheries, tourism, and power‑plant operations.

Ecologically, rhizostomeans are primarily filter feeders; the fused oral arms contain numerous stomatal openings that trap prey. Their diet consists mainly of zooplankton, phytoplankton, and detritus. Reproduction follows the typical scyphozoan life cycle, alternating between a sessile polyp (scyphistoma) and a free‑swimming medusa. Sexual reproduction occurs in the medusa stage, with gametes released into the water column.

Human interactions include occasional stings, which are generally mild, and commercial use of certain species for food and bioactive compounds. Ongoing research investigates their role in marine ecosystems, bloom dynamics, and potential applications in biotechnology.