Overview
The Japanese Sea Wasp (Carybdea brevipedalia), known locally in Japan as andon-kurage (lantern jellyfish), is a small but potent box jellyfish native to coastal waters of the northwest Pacific. Exhibiting the box-like cubic bell characteristic of the class Cubozoa, this agile pelagic invertebrate possesses true image-forming eyes and formidable cnidocyte-packed tentacles capable of delivering severe, painful stings to marine organisms and unsuspecting coastal swimmers.
Biology and Physical Characteristics
Carybdea brevipedalia possesses a translucent, cubic bell that measures roughly 3 to 4.5 centimeters in height. Dangling from the four corners of its umbrella are four muscular blade-like pedalia, each supporting a single retractable, contractile tentacle that can extend more than 30 centimeters during active foraging. Distributed around the rim of the bell are four sensory structures called rhopalia, each housing six distinct eyes—including two sophisticated lens eyes complete with corneas and retinas capable of detecting light direction, contrast, and stationary underwater obstacles.
Behavior and Ecology
Unlike true scyphozoan jellyfish that drift passively with ocean currents, box jellyfish are active, directional swimmers. Powered by a muscular shelf inside the bell rim called the velarium, Carybdea brevipedalia can propel itself forward at speeds up to two knots. It exhibits strong positive phototaxis, aggregating around coastal pier lights at night to feed on small fish larvae and mysid shrimp. When prey brushes against a tentacle, thousands of microscopic nematocysts discharge instantaneously, injecting potent pore-forming toxins that rapidly paralyze small aquatic prey.
Conservation and Human Impact
Widely distributed throughout the Japanese archipelago, Carybdea brevipedalia is not considered threatened. However, it represents a notable public health concern along popular swimming beaches during late summer, where blooms can cause painful cutaneous stings, erythema, and localized muscular cramping. Marine monitoring programs and beach warning flags are deployed during peak medusa emergence in August and September.
Interesting Factoid
Despite having no centralized brain, the Japanese sea wasp possesses 24 complex eyes, including camera-type lens eyes that can form real images, allowing it to actively navigate around obstacles and steer toward light.
Last updated: October 2026