Cubozoa
Box jellyfish (class Cubozoa) are cnidarian invertebrates known for their unique box-shaped bodies. Certain species of box jellyfish possess highly potent venom that can be delivered through contact with their tentacles. The stings from these species, such as Chironex fleckeri, Carukia barnesi, Malo kingi, and others, are exceptionally painful and often fatal to humans.
The bell of a box jellyfish takes on a square shape, giving the animal its distinct appearance. Hanging from each of the four lower corners of the bell is a short stalk called a pedalium, which bears one or more long, slender, hollow tentacles. The rim of the bell is folded inward to form a shelf called a velarium, which plays a role in restricting the bell's aperture and creating a powerful jet when the bell pulsates. This characteristic enables box jellyfish to move at faster speeds compared to other jellyfish, with recorded speeds of up to 6 meters (20 ft) per minute.
Inside the bell, there is a mobile appendage known as the manubrium, resembling an elephant's trunk, which houses the mouth. The gastrovascular cavity divides into a central stomach and four gastric pockets by four equidistant septa. The eight gonads are situated in pairs on each side of the four septa. These septa bear bundles of small gastric filaments, containing nematocysts and digestive glands, which aid in the capture and digestion of prey. Additionally, each septum extends into a septal funnel that facilitates the flow of fluid in and out of the animal through the oral surface.
The nervous system of box jellyfish is more advanced compared to other jellyfish. They possess a ring nerve at the base of the bell that coordinates their pulsing movements, a characteristic also observed in crown jellyfish. Box jellyfish stand out with their fully developed eyes, complete with retinas, corneas, and lenses. These eyes are clustered at the ends of sensory structures called rhopalia, connected to the ring nerve. Each rhopalium contains two lens eyes for vision. The upper lens eye has a field of view to observe the world above the water's surface, while the lower lens eye aids in object avoidance. The rhopalia also possess pit eyes, which act as light meters, and slit eyes to detect vertical movement. In total, each box jellyfish has 24 eyes across its four rhopalia, providing them with enhanced visual abilities.
Box jellyfish exhibit complex behaviors such as obstacle avoidance and fast directional swimming, suggesting guidance by the visual system. Their nervous system, especially within the rhopalia, facilitates visual processing and integration. This advanced sensory system has been likened to fish-like behavior. Depending on the species, a fully grown box jellyfish can measure up to 20 cm (8 in) along each side of the box and have tentacles reaching lengths of 3 m (10 ft). Despite their small size, thumbnail-sized species like the Irukandji jellyfish are lethal. The tentacles of box jellyfish possess cnidocytes, containing nematocysts that inject venom into their victims. These cnidocytes number approximately 500,000 per tentacle.
While the most dangerous species of box jellyfish are predominantly found in the tropical Indo-Pacific region, various species can be found in tropical and subtropical oceans across a wide range, including the Atlantic Ocean, east 🌊 Pacific Ocean, and other regions. Box jellyfish can be discovered in areas as far north as 🇺🇸 California, as far south as 🇿🇦 South Africa and 🇳🇿 New Zealand, and in the Mediterranean Sea and 🇯🇵 Japan. They tend to reside closer to shore in habitats like mangroves, coral reefs, kelp forests, and sandy beaches. The collection of data and studies on box jellyfish in the Indo-Pacific region is limited, with the first sightings of certain species only reported in recent years.
In 2023, a new species of box jellyfish named Gershwinia undefinedensis was discovered in the Indo-Pacific region, specifically in the Gulf of Thailand. Named after scientist L.A. Gershwin, this species stands out due to its unique sensory structures and the absence of a common digestive system found in other box jellyfish. The discovery of Gershwinia undefinedensis further expands our knowledge of the diverse range of box jellyfish species.
Box jellyfish are renowned for their powerful sting, which has been the subject of extensive research due to its lethality to humans. While some reports label the box jellyfish as the world's most venomous creature and the deadliest in the sea, it is important to note that only a few confirmed species in the class are known to be involved in human deaths. Some species may deliver stings that are no more than painful. The analysis of box jellyfish venom sequencing has revealed over 170 toxin proteins, contributing to their dangerous nature. Stings from box jellyfish can cause skin irritation, cardiotoxicity, and even be fatal.
To protect against box jellyfish stings, individuals can wear protective clothing such as pantyhose, full body lycra suits, dive skins, or wetsuits. Previously, it was believed that pantyhose provided protection due to the length of the jellyfish's stingers (nematocysts). However, it is now understood that the protection is related to the way stinger cells operate. The stinging cells on box jellyfish tentacles are triggered by chemical compounds found on the skin, which are absent on the outer surface of pantyhose. Thus, the nematocysts of box jellyfish do not discharge when coming into contact with the outer surface of pantyhose.
