Description: It is one of the largest and most conspicuous jellyfish of the southwestern Atlantic, belonging to the class Scyphozoa. The bell is robust and rounded, often exceeding 40 cm in diameter, with coloration ranging from whitish to pale brown or yellowish tones, sometimes darker toward the center. It lacks long marginal tentacles; instead, it has eight thick, highly branched oral arms densely covered with stinging structures used to capture prey. Its gelatinous body and slow, pulsating movements make it easily recognizable in coastal waters.

Geographic distribution: This species is mainly distributed along the western Atlantic Ocean, from southern Brazil to northern Patagonia in Argentina. It is particularly common in the Río de la Plata estuary and along the coasts of Uruguay and Buenos Aires Province, where seasonal mass occurrences are frequent. Its distribution is closely linked to regional oceanographic conditions such as water temperature and productivity.

Habitat: It inhabits shallow coastal and estuarine waters, showing a remarkable tolerance to wide salinity ranges. It is often found near the surface or within the upper water column, especially during calm sea conditions. Areas with high plankton availability favor its presence, making it an important component of coastal pelagic ecosystems.

Feeding: Its diet consists mainly of zooplankton, including copepods, crustacean larvae, fish eggs, and small fish. Prey capture occurs through stinging cells (cnidocytes) located on the oral arms, which paralyze organisms upon contact. Feeding is largely passive and depends on water currents bringing prey within reach.

Behavior: The species exhibits a mostly passive behavior, moving through rhythmic contractions of the bell. It can form large aggregations or blooms, driven by favorable environmental conditions and reproductive cycles. These blooms may influence local food webs by altering plankton dynamics and competing with planktivorous fish.

Reproduction: Like other scyphozoans, it has a complex life cycle with both sexual and asexual stages. Sexual reproduction occurs in the medusa stage, with gametes released into the water column. After fertilization, a free-swimming planula larva settles on the substrate, developing into a polyp that later produces juvenile medusae through strobilation.

Conservation status: The species has not been formally assessed at a global level. It is not currently considered threatened, and in some regions its increasing abundance has been associated with human-induced environmental changes, such as eutrophication and overfishing.

Author of this compilation: EcoRegistros – 01/18/2026