River Jelly

Acromitus flagellatus

Acromitus flagellatus is a jellyfish characterized by its bell-shaped body, which can reach up to 160 mm in diameter, often displaying uneven black or brown spots. It has eight oral arms that are approximately as long as the diameter of its bell, each ending in a long flagellum. This species is primarily found in brackish waters, such as mangroves and estuaries, and is commonly seen in the Western Indian Ocean and Central Pacific Ocean. Notable locations include the Bay of Bengal and coastal waters of Hainan Province. The River Jelly exhibits sluggish movement, relying on slow contractions to navigate through the water, occasionally assisted by fish like Caranx leptolepis. Feeding on zooplankton and ichthyoplankton, Acromitus flagellatus is an opportunistic feeder that also consumes copepods, phytoplankton, and other small marine organisms. Its life cycle involves sexual reproduction, where the medusa lays eggs that develop into a planula, then into a scyphistoma, followed by a strobila, and finally maturing into a medusa. Interestingly, it does not feed during the egg or strobila stages, only during the planula and medusa stages. Encounters with this jellyfish on dives may reveal its tranquil nature, as it drifts slowly through the water. Swarms of Acromitus flagellatus can occur due to environmental changes, potentially impacting local ecosystems and human activities. The species has not been evaluated for conservation status, but its ecological role is significant, particularly in mangrove and estuarine environments.