rhizostomatids

Rhizostomatids are jellyfish in the family Rhizostomatidae, within the order Rhizostomeae of the class Scyphozoa. They are commonly called rhizostomes. Members are characterized by a bell-shaped medusa with a mouth located on the underside, surrounded by enlarged, fused oral structures rather than a single peripheral mouth with long marginal tentacles. The tentacles are often reduced or absent in adults, and the oral arms form a complex, lobed region around the central mouth.

They inhabit coastal and shelf waters in warm and temperate seas worldwide, including bays, estuaries, and coral-reef environments. Feeding is mainly by capturing plankton and small organisms with the mucous membranes around the oral region; the morphology supports a suction-like feeding mechanism without long marginal tentacles. The life cycle follows the typical scyphozoan pattern, with a sessile polyp stage producing medusae through asexually budding polyps, and sexual reproduction producing planula larvae that settle into new polyps.

Ecology and human interactions: Rhizostomatids can form large blooms under favorable conditions and contribute to local zooplankton dynamics. They are preyed upon by some fish, sea turtles, and invertebrates. Stings from rhizostome medusae can cause irritation or more intense reactions in sensitive individuals, depending on the species.

Taxonomy: The Rhizostomatidae family is diverse, with multiple genera and species. Ongoing research, including molecular analyses, continues to refine their relationships within Rhizostomeae and related jellyfish groups.