Description: It is a small to medium-sized hydrozoan jellyfish, notable for its delicate structure and striking coloration. The bell is hemispherical and transparent, typically measuring 4–8 cm in diameter, with a well-defined margin from which numerous thin tentacles extend. These tentacles often display greenish, bluish, or purplish hues, making the species highly distinctive. A short central manubrium is visible, and the internal structures can be easily observed due to the high transparency of the body. Despite its fragile appearance, it possesses powerful stinging cells, capable of causing painful stings to humans.

Geographic distribution: The species is distributed in the southwestern Atlantic Ocean, with confirmed records from southern Brazil to the coast of Argentina. It is particularly common along the Uruguayan coast, the Río de la Plata, and Buenos Aires Province, where its occurrence is typically seasonal. Its distribution is strongly influenced by oceanographic factors such as water temperature, coastal currents, and plankton dynamics.

Habitat: It mainly inhabits coastal marine environments, including shallow waters near beaches and areas influenced by estuaries. It is a pelagic species, associated with the upper layers of the water column, although it may perform limited vertical movements. It prefers temperate waters with high plankton availability and is more frequently observed during warmer months.

Feeding: Its diet consists primarily of zooplankton and small pelagic organisms, such as crustacean larvae, copepods, and juvenile fish. Prey capture occurs through tentacles armed with cnidocytes, which quickly immobilize organisms upon contact. The prey is then transported to the mouth by coordinated movements of the manubrium. It plays an important role as an intermediate predator in coastal food webs.

Behavior: The species exhibits a mostly passive behavior, moving through gentle bell pulsations and largely drifting with currents. Individuals may be observed alone or forming localized aggregations, particularly under favorable environmental conditions. It is known to occasionally approach coastal areas, increasing the likelihood of encounters with swimmers.

Reproduction: It has a typical hydrozoan life cycle, alternating between a sexual medusa stage and an asexual polyp stage. Sexual reproduction occurs in the medusa, with gametes released into the water column. After fertilization, a planula larva develops and gives rise to a microscopic polyp, which later produces new medusae by budding, completing the life cycle.

Conservation status: The species has not been specifically assessed at a global level. It is not considered threatened, and its populations show natural fluctuations mainly related to environmental and oceanographic variability, with no current evidence of sustained population decline.

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