Facts: The Compass Jellyfish

The compass jellyfish is a common jellyfish species that inhabits the temperate coastal waters of the northeastern Atlantic Ocean, including the Mediterranean Sea and the North Sea. In the past, compass jellyfish were also recorded in the southeastern Atlantic, but this was caused by confusion with close relatives. Compass jellyfish typically drift near the surface, but they may be spotted down to 500 feet deep. They are often found inshore, especially at dusk. Their coloration varies from transparent to yellow-white. They have distinct brown markings that are shaped like elongated Vs on their bell. The markings surround a central dark circle. Their diameter is typically 6 to 10 inches. They can swim by contracting and relaxing their bell. Adults have 24 tentacles, arranged in eight groups of three. The tentacles contain stinging cells that the jellyfish use for defense and for capturing prey. Each stinging cell is like a capsule, inside of which is a long, coiled thread. The thread shoots out like a harpoon to inject prey with venom. The jellyfish also have four frilly oral arms. The mouth is located in between the oral arms on the underside of the bell. The oral arms are used to facilitate transfer of captured prey from the tentacles to the mouth. The jellyfish consume a variety of marine invertebrates and plankton. Compass jellyfish are protandric hermaphrodites. Free-swimming adults start off as male and then later become female. Their life cycle consists of two forms, a free-swimming medusiform and an attached polyp form. This allows compass jellyfish to reproduce both sexually and asexually. Adult females produce eggs that are fertilized by male jellyfish. The fertilized eggs hatch into larvae that eventually settle and become attached polyps. Polyps bud off tiny larval jellyfish that eventually develop into adults. Sometimes compass jellyfish wash up on beaches in mass numbers. For more marine facts, click the SUBSCRIBE button!!