Compass Jelly

Overview

The Compass Jellyfish is a distinctive, saucer-shaped medusa easily recognized by the 16 brown, V-shaped radial markings on its bell that resemble a compass rose. This pelagic species is commonly found in the coastal waters of the northeastern Atlantic Ocean, the North Sea, and the Mediterranean Sea. It is a carnivorous predator that plays a significant role in local marine food webs.

Appearance

This jellyfish features a translucent, yellowish-white bell that typically measures between 10 and 30 cm in diameter, though some individuals can grow larger. The bell's margin is divided into 32 lobes and supports 24 long, thin tentacles arranged in eight groups of three. Beneath the bell, four thick, frilly oral arms extend significantly, often reaching lengths of up to 2 meters. These arms and the marginal tentacles are equipped with potent stinging cells used for defense and capturing prey.

Biology & behavior

The Compass Jellyfish follows a complex life cycle, alternating between a stationary benthic polyp stage and a free-swimming pelagic medusa stage. Unlike many other jellyfish, this species is a sequential hermaphrodite, typically maturing as a male before transitioning into a female. They are generally short-lived, with a lifespan of approximately one year. While they are capable of active swimming through bell pulsations, they are often observed drifting in coastal currents and may move vertically in the water column to maintain their position or avoid rough surface conditions.

Feeding

As a carnivore, the Compass Jellyfish feeds on a variety of plankton, small crustaceans, fish larvae, and occasionally other jellyfish. It uses its stinging tentacles to stun prey, which is then transferred to the mouth by the frilly oral arms. In some instances, they have also been observed consuming small benthic organisms.