Cannonball Jellyfish

About

The cannonball jellyfish (Stomolophus meleagris) is one of the more recognizable medusae along North American coastlines, named for its round, dome-shaped bell that really does look like a cannonball rolling through the water column. It ranges across Atlantic and eastern Pacific coastal seas, often appearing in enormous seasonal blooms that can clog fishing nets and overwhelm shorelines. The bell is typically creamy white to yellowish with a distinctive brownish pigmented border, and instead of long trailing tentacles it has a dense cluster of short, frilly oral arms beneath the bell that it uses to filter zooplankton and small organisms from the water. This species is completely peaceful in the sense that it drifts passively, but do not mistake peaceful for easy. Cannonballs are genuinely advanced animals to keep. They absolutely require a purpose-built kreisel tank, a circular flow system designed to keep the animal suspended in a gentle current without it getting sucked against intakes or tumbled into walls. They cannot be housed with fish or other invertebrates in a conventional aquarium setup. For anyone willing to invest in proper equipment, a healthy cannonball in a well-maintained kreisel is a genuinely striking display, but this is one species where cutting corners will quickly end badly.